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Abstract

Regulatory T-cells (T_REG) are diverse populations of lymphocytes that regulate the adaptive immune response in higher vertebrates. T_REG delete autoreactive T-cells, induce tolerance, and dampen inflammation. T_REG cell deficiency in humans (i.e., IPEX [Immunodysregulation, Polyendocrinopathy and Enteropathy, X-linked syndrome]) and animal models (e.g., “Scurfy” mouse) is associated with multisystemic autoimmune disease. T_REG in humans and laboratory animal species are similar in type and regulatory function. A molecular marker of and the cell lineage specification factor for T_REG is FOXP3, a forkhead box transcription factor. CD4⁺ T_REG are either natural (nT_REG), which are thymus-derived CD4⁺CD25⁺FOXP3⁺ T-cells, or inducible (i.e., Tr1 cells that secrete IL-10, Th3 cells that secrete TGF-β and IL-10, and Foxp3⁺ Treg). The proinflammatory Th17 subset has been a major focus of research. T_H17 CD4⁺ effector T-cells secrete IL-17, IL-21, and IL-22 in autoimmune and inflammatory disease, and are dynamically balanced with T_REG cell development. Other lymphocyte subsets with regulatory function include: inducible CD8⁺ T_REG, CD3⁺CD4⁻CD8⁻ T_REG (double-negative), CD4⁺Vα14⁺ (NKT_REG), and γδ T-cells. T_REG have four regulatory modes of action: secretion of inhibitory cytokines (e.g., IL-10 and TGF-β), granzyme-perforin-induced apoptosis of effector lymphocytes, depriving effector T-cells of cytokines leading to apoptosis, or inhibition of dendritic cell function. The role of T_REG in mucosal sites, inflammation/infection, pregnancy, and cancer as well as a review of T_REG as a modulatory target in drug development will be covered.

Keywords

immunopathology;regulatory T-cells;lymphocytes;flow cytometry;Scurfy mouse;FOXP3;IPEX.

Introduction to Regulatory T-Cells

This article will review the scientific literature and provide an overview of Regulatory T-cell (T_REG) characterization, function, role in the immune response, at mucosal sites, during pregnancy and in the tumor microenvironment, and as a target for modulation in drug development. There has been enhanced focus on the T_REG in the field of immunology, which translates into a prominent increase in the number of citations over the past decade (Figure 1).

Figure 1.

There has been a steady increase in the number of regulatory T-cell (T_REG) citations in the scientific literature from the mid-1990s to the present (from Scopus). The key milestones in T_REG research are highlighted on the horizontal axis.

T_REG are diverse populations of lymphocytes that regulate the adaptive immune response in higher vertebrates. T_REG delete autoreactive T-cells, induce tolerance, and dampen inflammation (Akdis 2009; Ozdemir et al. 2009; Dittel 2008; Orihara et al. 2008; Sakaguchi et al. 2008; Simpson 2008; Bluestone and Tang 2005; Coutinho et al. 2005).

Over the past 40 years, the field of immunology has slowly evolved, becoming much more complex than was initially hypothesized in the 1960s. Between 1966 and 1968, several groups identified B-lymphocytes as the source of the antibody response and T-lymphocytes as critical in the delayed-type hypersensitivity (DTH) response (Claman et al. 1966; Mosier 1967; Mitchell et al. 1968). In 1971, Gershon and Kondo identified negative interference on positively acting lymphocytes during inflammation and referred to it as “infectious immunological tolerance” (Gershon and Kondo 1971). This was the first indication that a “suppressive” process was active during inflammation. The “suppressor T-cell” hypothesis was put forth by two groups in the later years of the 1970s (Vadas et al. 1976; Okumura et al. 1977). A series of negative results from experiments conducted by several groups led to a loss of confidence in the “suppressor T-cell” hypothesis, rejection of the hypothesis by the field of immunology, and more recently reacceptance (Kapp and Bucy 2008; Germain 2008; Lehner 2008). The rejection of the “suppressor T-cell” hypothesis did not explain away the presence of a dampening of immune responses commonly seen in the inflammatory milieu. In 1989, Mosmann and Coffman identified the T-helper (T_H)-1 and (T_H)-2 CD4⁺ T-cell subsets based upon the profiles of cytokines secreted after activation. T_H1 cells primarily secrete IFN-γ, IL-15, and TNF-α, while T_H2 cells secrete IL-4, IL-5, IL-6, and IL-13. Powrie et al. showed in severe combined immunodeficient (SCID) mice that subsets of CD4⁺ T-cells induce and protect from intestinal inflammation (Powrie et al. 1994). This once again defined a population of lymphocytes with immunosuppressive actions, which was identified as a population expressing CD45RB^low while the inducing cells were CD45RB^high. In 1995, Sakaguchi et al. found that immunologic self-tolerance was maintained by activated CD4⁺ T-cells expressing CD25 (IL-2R alpha chain). Depletion of this CD4⁺CD25⁺ population led to development of autoimmune disease (Sakaguchi et al. 1995). Two groups, Hori et al. and Fontenot et al., identified a CD4⁺CD25⁺FOXP3⁺ cell population that was found to be thymically derived, natural T_REG cells (Hori et al. 2003; Fontenot et al. 2003, 2005). FOXP3 has been shown to be critical for regulatory action of most subtypes of T_REG.

Types of Regulatory T-Cells (T_REG, Natural, and Adaptive/Induced) CD4⁺CD25⁺ T_REG

Natural T_REG are thymus-derived CD4⁺CD25⁺FOXP3⁺ T-cells (Figure 2). They arise in the thymus during early stages of human fetal development (gestational week 14) (Cupedo et al. 2005) and are resistant to thymic deletion (Lim et al. 2006). nT_REG differentiate from thymocytes that express TCRs with an increased affinity for self-peptide-MHC complexes (Lim et al. 2006; Maggi et al. 2005; Schwartz 2005). nT_REG can suppress the following cell types: CD4+ T-cells, dendritic cells, CD8⁺ T-cells, NKT cells, NK cells, monocytes/macrophages, B-cells, mast cells, basophils, eosinophils, and osteoblasts (Shevach et al. 2009; Lim et al. 2006). FOXP3⁺expression is necessary for thymocytes to commit to the T_REG lineage (Lim et al. 2006). Resting nT_REG are CD45RA⁺FOXP3^low, while activated nT_REG are CD45RO⁺FOXP3^high(Beissert et al. 2006; Lim et al. 2006). Natural T_REG also express the following markers: T cell activation/differentiation markers (CD45RO [memory phenotype; activated], CD45RB [resting], CD25 [both]), adhesion molecules (CD62L [both], CD44 [both] and Integrin α₄β₇ [resting]), cytotoxic T lymphocyte-associated protein-4 (CTLA-4; both), co-stimulatory molecule CD28 (both), chemokine receptors (CCR7 [both], CXCR4 [both], CCR9 [resting]), glucocorticoid-induced TNFR-related protein (GITR, both), OX40 (CD134, both), and folate receptor-4 (FR4 in rodents, both) (Lim et al. 2006). IL-2 is essential for nT_REG development, function, and homeostasis (i.e., CD25 is the α-chain of the high affinity IL2R) (Malek et al. 2008). Severe autoimmunity is seen in IL-2-, IL2Rα-, and IL-2Rβ-deficient mice, which also lack a normal number of T_REG cells (Malek et al. 2008). The nT_REG profile in mammals is highly conserved. Nonhuman primates have the same nT_REG protein expression and functional profile as that of humans including two FOXP3 isoforms (Roncarolo and Battaglia 2007; Bloom 2006), while in rodents there are only subtle differences primarily in the type of granzyme expressed (i.e., B versus A) and only a single FOXP3 isoform (Roncarolo and Battaglia 2007).

Figure 2.

T_REG are either formed naturally by thymic differentiation (nT_REG) or are induced in the periphery (iT_REG) from naïve T-cells (T_H0). Types of iT_REG include T_H3, T_r1, which are CD4⁺CD25⁺FOXP3⁺, and CD4⁺CD25^-FOXP3⁺ iT_REG. The main effector CD4+ subsets are T_H1, T_H2, and T_H17. The cytokines that are important in inducing these cells from T_H0 cells and the cytokines that these cells secrete are listed.

Adaptive/Induced T_REG

The two most common types of adaptive or induced T_REG are the T regulatory type 1 cells (T_r1) and T_H3 T_REG cells (Figure 2). T_r1 cells secrete IL-10 and also have an IL-10-dependent induction process (Fujio et al. 2010; Beissert et al. 2006; Roncarolo et al. 2006). They are capable of secreting high levels of IL-10 and TGF-β in the human and mouse and also secrete low levels of IL-2, IL-5, and IFN-γ (Fujio et al. 2010; Roncarolo et al. 2006). An important growth factor for T_r1 cells is IL-15, which can support T_r1 cell proliferation even without TCR activation (Fujio et al. 2010; Roncarolo et al. 2006). They are CD4+, anergic, and proliferate poorly upon antigen-specific activation which is likely due to the autocrine production of IL-10 leading to suppression of proliferation (Fujio et al. 2010; Roncarolo et al. 2006). The mechanism of suppressive effects with T_r1 cells is soluble factor-based (i.e., IL-10), and the suppressive effects of T_r1 cells are negated by anti-IL-10 neutralizing antibody in vitro (Fujio et al. 2010; Roncarolo et al. 2006). There is no specific marker for T_r1 cells, although repressor of GATA-3 (ROG) shows potential utility (Fujio et al. 2010; Roncarolo et al. 2006), but it is not specific for this cell population.

T_H3 cells secrete TGF-β and IL-10 and express FOXP3 (Beissert et al. 2006). They are induced from naïve CD4⁺ T-cells by TGF-β and have an important role in oral tolerance to non-self antigens and negating autoimmune reactions (Wan and Flavell 2007). T_H3 cells secrete TGF-β, which has immunosuppressive effects acting through a soluble-factor mechanism. T_H3 cells have a reciprocal relationship with T_H17 cells (Korn et al. 2009; Nistala and Wedderburn 2009). T_H17 cells are highly proinflammatory and are thought to be important in autoimmune disease (Abraham and Cho 2009; Crome et al. 2009; Korn et al. 2009; Nistala and Wedderburn 2009; Romagnani et al. 2009); this will be discussed in detail later in the article. There has been no specific surface marker identified for T_H3 cells, although expression of FOXP3 is induced in T_H3 cells (i.e., cannot differentiate from nT_REG) (Korn et al. 2009).

Other T-Cells with Regulatory Function

Other T-cell populations that have been shown to have regulatory function include inducible CD8⁺ T_REG cells, CD8⁺CD28⁻ T_REG cells, and CD3⁺CD4⁻CD8⁻ T_REG (double-negative [DN]). CD8⁺ T_REG (Kapp and Bucy 2008; Beissert et al. 2006; Nakamura et al. 2003; Ke and Kapp 1996; Jiang et al. 1992) are CD8⁺ T-cells that have regulatory activity on CD4⁺ T_H1 cells. This T_REG population inhibits priming of CD8⁺ T-cells, CD4⁺ T-cells, and antibody responses against oral antigens. They are induced by manipulation of co-stimulatory molecule interactions (i.e., CD137 and CD40) primarily, although antigens introduced into immune privileged sites (i.e., anterior chamber of eye leading to anterior chamber-associated autoimmune deviation [ACAID]) elicit CD8⁺ T_REG due to high levels of TGF-β and IL-10 at this site (Biros 2008; Niederkorn 2008). They have also been shown to arise spontaneously in Experimental Allergic Encephalitis (EAE) and murine Ovalbumin-induced oral tolerance models and in tumor-bearing hosts due to IL-10 secretion by APCs in the neoplasm. They are well characterized in rodents, but their importance in humans is uncertain. CD8⁺CD28^-T_REG (Cortesini et al. 2001; Chang et al. 2002) are FOXP3⁻ and are induced by inhibitory immunoglobulin-like transcript (ILT)-3 and ILT-4 receptor expression on dendritic cells and down-regulation of CD80 and CD86. They interfere with the CD28/B7 pathway with allogeneic antigens and CD154/CD40 pathway with xenogeneic antigens. CD8⁺CD28⁻ T_REG regulate immune responses by direct cell-to-cell interactions with dendritic cells; therefore they are directly tolerogenic. This cell population has been described in rodents and humans. CD3⁺CD4⁻CD8⁻ (DN) T_REG are TCRαβ⁺, CD4⁻, and CD8⁻ (therefore DN). They promote the development of tolerance and regulate autoimmunity (Strober et al. 1996). This cell population has been defined and characterized in heart xenotransplantation experiments (Chen et al. 2003, 2005; Zhang et al. 2006; Ma et al. 2008). DN T_REGare poorly suppressive in naïve mice but are actively suppressive in recipients of heart xenografts co-transferred with donor DN Tregs. They have been shown to prevent heart xenograft rejection (i.e., transplant tolerance). It has been shown that antigen presenting cells (APC) from tolerant mice had down-regulation of MHCII, CD40, and B7 molecules, and likely were in an immature state. The significance of DN T_REG in nontransplant scenarios is therefore uncertain and more data is needed.

CD4⁺Vα14⁺ (NKT_REG)

Natural killer T-cells coexpress NK receptors (i.e., NK1.1 or CD161) as well as a conserved T-cell receptor (TCR) molecule (Beissert et al. 2006), Vα14. Vα14 pairs with Vβ8 in the mouse and Vβ11 in the human and are restricted by CD1d, a conserved MHCI-type molecule that presents glycolipids. NKT_REG cells are generated in the thymus and can be CD4⁺, CD8⁺, DN, or double positive (DP). In mice, DN NKT_REG are the dominant phenotype (Zeng et al. 1999); while in humans, CD4⁺ NKT_REG are most efficient (Jiang et al. 2005). They have been studied primarily in rodent xenogeneic transplantation models (Ikehara et al. 2000). They secrete IL-4, IL-10, TGF-β (paracrine), and induce cytotoxicity by cell-to-cell contact, and the targets of NKT_REG cells are T-cells and APCs (Ikehara et al. 2000; Zeng et al. 1999). The significance of NKT_REG cells in immune regulation outside of xenotransplantation is uncertain.

γδ T-Cells (Mucosal/Intraepithelial)

Gamma delta (γδ) T-cells, which express TCRγδ and have a mucosal distribution, are primarily suppressive and are associated with mucosal tolerance (Kapp and Ke 1997; Ke et al. 1997; Mowat 1994), but can also function to regulate autoimmunity (Weiner et al. 1994), elicit ACAID in the eye (Biros 2008), and function in tumor immunity (Seo et al. 1999). These cells do not recognize peptides associated with MHC receptors (Kronenberg 1994); alternatively they recognize cellular proteins including heat shock proteins (Munk et al. 1989) and nonclassic MHC molecules like CD1 (Brossay et al. 1998) and Qa-1 (Vidovic et al. 1989). γδ T-cells that infiltrate tumors have cytokine profiles that are similar to T_r1 cells (i.e., IL-10 and TGF-β) and inhibit the immune response against neoplasia (Kapp et al. 2004; Seo and Tokura 1999; Seo et al. 1999; Kapp and Ke 1997; Ke et al. 1997). Therefore, γδ T-cells are a minor population of mucosal and intratumoral T-cells with regulatory activity and major roles in mucosal tolerance and tumor immunity.

A Non-T Lymphocyte Subset with Regulatory Function

Another cell type exhibiting regulatory activity is the regulatory B-cell (B_REG) which has been recently reviewed by Li et al. (2011). B_REG cells are beyond the scope of this review, but are mentioned here briefly to showcase the diversity of lymphocytes with regulatory function in the immune system and for completeness-sake. B_REG cells have been shown in various animal disease models, including collagen-induced arthritis (Trentham et al. 1977), experimental autoimmune encephalitis (EAE) (Wolf et al. 1996), nonobese diabetes mellitus (Tian et al. 2001), inflammatory bowel disease (Mizoguchi et al. 2000), and systemic lupus erythematosus (Lenert et al. 2005), and function primarily to regulate T-cells, B-cells, and NKT cells. B_REG cells act by soluble factor-based means by secreting IL-10 (Reigert and Bar-Or 2008), TGF-β (Takenoshita et al. 2002) and producing anti-inflammatory antibodies (Diamond et al. 2003). Cell-cell interactions are an important mode of B_REG regulatory function and include CD1d binding (Yanaba et al. 2008) by CD1d^hiCD5⁺ cells and CD40/CD40 L interactions (Quezada et al. 2004). More research into specific roles for B_REG is needed to more completely define this cell type.

T_REG Basics

T_REG cells function at sites of inflammation in close spatial proximity to effector T-cells, thus allowing direct interactions between the two cell types (Askenasy et al. 2008). T_REG cells are attracted by inflammatory signals, although they are less chemotactic than effector T-cells (Siegmund et al. 2005). When arriving at the site of inflammation, T_REG down-regulate chemotactic receptors and adhesive interactions to arrest further migration (Siegmund et al. 2005). nT_REG are mitotically inactive under basal conditions (Kuniyasu et al. 2000). Activated T_REG-mediated immune suppression is antigen-nonspecific (i.e., not MHCII-restricted) (Bienvenu et al. 2005), although induction of suppressor function in T_REG requires antigen-specific stimulation (i.e., via TCR) leading to tissue-specific suppressive effects (“bystander” suppression) (Shevach 2009; Weiner 1997). T_REG have also been associated with regulating lymphopenia-induced lymphocyte proliferation, which is a normal homeostatic event that occurs after lymphopenia of numerous causes including those of a physiologic and pathologic nature. Lymphopenia-induced lymphocyte proliferation does not increase the number of naïve lymphocytes, but instead the number of memory T-cells increase, which might result in potential self-reactive clones and subsequent autoimmunity. T_REG have an important role in regulating this process (Datta and Sarvetnick 2009).

Effects of Acute and Chronic Stress on Human T_REG

βeta 1-adrenergic and glucocorticoid α receptors are overexpressed in T_REG versus effector T-cells (Freier et al. 2010; Atanackovic et al. 2006). These receptors likely mediate T_REG responses to stress (Freier et al. 2010; Atanackovic et al. 2006). T_REG numbers have been shown to decrease with acute physiologic stress (Freier et al. 2010; Atanackovic et al. 2006; Atanackovic et al. 2002). Based on these findings, chronic stress could exacerbate autoimmune disease and other inflammatory conditions (Freier et al. 2010).

Modes of Action of T_REG Regulation

T_REG have primary effect on T-cells and/or dendritic cells by three main regulatory modes of action: (1) soluble factors (Figure 3), (2) cell-to-cell contact (Figure 4) and (3) competition for growth factors (local effect) (Figure 5). Soluble factors include IL-10 and TGF-β with direct suppressive effects on effector T-cells (Joetham et al. 2007; Annacker et al. 2003), fibrinogen-like protein-2 (FLG-2) with apoptotic effects on effector T-cells and prevention of maturation of dendritic cells (Shalev et al. 2009), granzyme A/B and perforin apoptotic effects on effector T-cells (Grossman et al. 2004), and production of adenosine by CD39/73 cleavage of ATP, which causes cell cycle arrest in effector T-cells and prevention of maturation and decreased antigen presenting capability in dendritic cells by binding to the A_2A receptor on these cell types (Deaglio et al. 2007). Galectin-1 binding to effector T-cells and dendritic cells resulting in cell cycle arrest and/or apoptosis (Garin et al. 2007), CTLA4 and CD80/86 binding to dendritic cells causing decreased costimulation and decreased antigen presentation (Read et al. 2000), lymphocyte activating gene-3 (LAG3 or CD223, a CD4 homolog) binding to MHCII molecules on dendritic cells leading to prevention of maturation and a reduction in antigen presentation capability (Workman and Vignali 2004), and neuropilin-1 binding to dendritic cells resulting in decreased antigen presentation (Sarris et al. 2008) are examples of cell contact-based mediated effects of T_REG. T_REG can also deny IL-2 to other inflammatory cells by binding the cytokine and acting as a “sink” leading to effector T-cell apoptosis (Pandiyan et al. 2007). Therefore, T_REG have a variety of mechanisms that can be used to suppress an immune response and are able to use all or a subset of these mechanisms simultaneously.

Figure 3.

T_REG can cause suppression of effector T-cells and dendritic cells through secretion of soluble factors including IL-10, TGF-β, fibrinogen-like protein-2 (FLG-2), granzyme A or B and perforin, and adenosine. The figure shows the signaling pathways and the suppressive effects on effector T-cells and dendritic cells.

Figure 4.

T_REG can cause suppression of effector T-cells and dendritic cells through cell contact-based mechanisms, including galectin-1 binding, CTLA-4 binding to CD80/86, lymphocyte activation gene-3 (LAG-3) binding to MHCII molecules, and neuropilin-1 binding. The figure shows the ligands, receptors, and the suppressive effects on effector T-cells and dendritic cells.

Figure 5.

T_REG can cause suppression of effector T-cells by providing competition for growth factors (primarily IL-2), which is essential for their survival in the periphery. T_REG express multiple copies of IL-2R/CD25, which bind up local IL-2 competing with effector T-cells for IL-2 stimulation. The figure shows the ligands, receptors, and the suppressive effects on effector T-cells.

T_REG Markers (Immunohistochemistry, Flow Cytometry, Intravital Microscopy, and miRNA Analysis)

Immunofluorescent and chromogenic IHC and flow cytometry (de Boer et al. 2007; Roncador et al. 2005) for the following markers has been shown to be useful in characterizing T_REG in tissue sections and isolated cells: FOXP3 (Figures 6, 7, 8, and 9), CD25 (alpha chain of IL2R) (Figures 7, 8, and 9), and CD62L (L-Selectin) (Figures 6 and 7). Intercellular interactions of T_REG cells and effector T-cells have been visualized in rodent models using intravital microscopy (Tang and Krummel 2006). Differences in micro-RNA (miRNA) in human T_REG versus effector T-cells have been shown (Hezova et al. 2010). There was a significant increase in miR-146a and decreases in miR-20b, 31, 99a, 100, 125b, 151, 335, and 365 in T_REG when compared with effector T-cells. The pattern of increased expression of miR-146a in combination with decreases in the other miRNAs is a possible marker of T_REG.

Figure 6.

FOXP3 and CD3 dual immunofluorescence on tissue from an area of inflammation. Note the green nuclear labeling (FOXP3⁺) and the red cytoplasmic labelling (CD3⁺). The image shows a group of T-cells with several FOXP3⁺ T_REG cells in the field. 400× magnification.

Figure 7.

Flow cytometry was performed on blood from male and female CD-IGS rats to evaluate the percentage of CD4⁺CD25⁺CD62L⁺FOXP3⁺ (nT_REG and iT_REG) cells. The image highlights the gating strategy and steps used in this evaluation.

Figure 8.

The graphs of flow cytometry data using markers useful in characterizing T_REG show the percentage of CD3⁺CD4⁺ cells, CD62L⁺ cells in the CD3⁺CD4⁺population, CD25⁺cells in the CD3⁺CD4⁺ population, and FOXP3⁺ cells in the CD3⁺CD4⁺ population cell subsets in male and female rats. There was no definitive difference in cell percentages between males and females in this evaluation.

Figure 9.

The graphs of flow cytometry data show the percentages of FOXP3⁺ cells in the CD4⁺CD25⁺ population and CD25⁺ cells in the CD4⁺FOXP3⁺ population. The majority (approximately 80%) of CD4⁺CD25⁺ cells are also FOXP3⁺, which would include nT_REGand T_H3 cells. Only a minority (approximately 30%) of CD4⁺FOXP3⁺ cells are also CD25⁺, which means approximately 70% of the CD4+FOXP3+ population likely represents an iT_REG cell population.

FOXP3: Function and Biology

FOXP3, a forkhead box transcription factor, is a molecular marker and cell lineage specification factor for T_REG (Fontenot et al. 2003; Hori et al. 2003). FOXP3 is critical for the thymic differentiation of αβ TCR⁺ thymocytes into nT_REG (Sakaguchi et al. 2008; Fontenot et al. 2003; Hori et al. 2003). The FOXP3 gene product is referred to as scurfin and functions by regulating a set of genes required for (1) the suppressor activity of T_REG, proliferative, and metabolic fitness of T_REG and (2) repressing alternative T cell differentiation pathways (Brunkow et al. 2001). It has been shown that a higher level of expression of FOXP3 is sufficient for suppressive activity of non-T_REG T-cells in rodents (Sakaguchi et al. 2008; Lourenco and La Cava 2011). Several pathways are important in the induction of FOXP3 expression including TGF-β, IL-2, retinoic acid, 17-β-estradiol, and signaling through the sphingosine-1-phosphate receptor 1 (S1PR1) (Figure 10). TGF-β is essential for induction of FOXP3 expression in naïve T-cells (i.e., iT_REGincluding T_H3 cells), but in the human it does not necessarily confer regulatory function (Lourenco and La Cava 2011).

Figure 10.

The figure highlights several pathways of induction of FOXP3 expression including the ligands, receptors, and/or intermediary steps in induction of gene expression. A schematic of the FOXP3 gene shows the promoters and important transcription factors that bind to the promoters. There are 11 coding exons in both the mouse and human FOXP3 genes.

FOXP3 Deficiency

The “Scurfy” Mouse

In mice (B.Cg-Foxp3^sf ), a frameshift mutation in the FOXP3 gene results in a truncated protein lacking the forkhead domain and is responsible for the “Scurfy” phenotype (Clark et al. 1999; Ochs et al. 2002; Patel 2001). Scurfy is an X-linked recessive mutation in the mouse that is lethal in hemizygous males 16 to 25 days after birth (Ochs et al. 2002; Godfrey et al. 1991). Scurfy mice have an overproliferation of CD4⁺ T-lymphocytes and other cell types due to uncontrolled cytokine secretion with extensive multiorgan infiltration due to lack of functional T_REG(Ochs et al. 2002; Godfrey et al. 1991). Lymphadenopathy, parenchymal organ infiltration, and subcutaneous inflammatory cell infiltrates (e.g., ear pinnae) are prominent (Figures 11 and 12) (Godfrey et al. 1991). The phenotype of Scurfy mice is similar to mouse models that lack CTLA-4 or TGF-β, and in humans with immunodysregulation, polyendocrinopathy and enteropathy, X-linked syndrome (IPEX) (Clark et al. 1999; Ochs et al. 2002; Patel 2001).

Figure 11.

The “Scurfy” mouse has a frameshift mutation in the forkhead box transcription factor, FOXP3. This results in early lethality due to unregulated inflammation (parenchymal organs, subcutis, and lymphoid organs are the main sites of inflammatory cell accumulation) due to the lack of functional T_REG cells. Note the gross pathology image of a Scurfy mouse with marked hepato- and splenomegaly and evidence of subcutaneous lesions at the tail base.

Figure 12.

Note the prominent mononuclear inflammatory cell accumulation in the dermis and upper subcutis from a “Scurfy” mouse. Hematoxylin and eosin, 200× magnification.

IPEX in Humans

IPEX is a rare human multisystemic autoimmune disease (X-linked: females are carriers, males have the disease) that is linked to the dysfunction of the transcriptional activator FOXP3 which results in dysfunction of regulatory T-cells with subsequent autoimmunity (Ochs et al. 2002). Mutations in the forkhead domain of FOXP3 disrupt FOXP3 protein: DNA interactions (Ochs et al. 2002; Patel 2001). The disorder manifests with enteropathy, food allergy, massive lymphoproliferation, psoriasiform or eczematous dermatitis, nail dystrophy, autoimmune endocrinopathies (primarily insulin-dependent diabetes mellitus and autoimmune thyroid disease), Coombs-positive anemia, autoimmune thrombocytopenia, autoimmune neutropenia, tubular nephropathy, and autoimmune skin conditions such as alopecia universalis and bullous pemphigoid (Ochs et al. 2002). Treatment for IPEX includes immunosuppressive agents (e.g., cyclosporin A, FK506) alone or in combination with steroids (Ochs et al. 2002). There has been limited success in treating the syndrome with bone marrow transplantation (Ochs et al. 2002).

T_H17 cells and T_REG: A Reciprocal Balance

T_H17 cells are a subpopulation of effector T cells that are very pro-inflammatory and implicated in allergic/autoimmune disease (Abraham and Cho 2009; Crome et al. 2009; Korn et al. 2009 and 2007; Nistala and Wedderburn 2009; Romagnani et al. 2009). T_H17 cells secrete IL-17, IL-22, IL-21 and IL-17F (Korn et al. 2009, 2007; Veldhoen et al. 2006; Bettelli et al. 2006; Mangan et al. 2006). TGF-β is critical in induced/adaptive T_REG cell (i.e., T_H3 T_REG) differentiation as well as development of T_H17 effector cells (Wan and Flavell 2007) (Figure 13). Naïve T-cells develop into a “transitional” cell-type that expresses FOXP3 (T_H3 T_REG cell marker) and ROR-γt and RORα (T_H17 effector cell markers) in the presence of TGF-β (Figure 14) (Nistala et al. 2009; Korn et al. 2007; Veldhoen et al. 2006; Bettelli et al. 2006; Mangan et al. 2006). Further exposure to TGF-β or IL-6/IL-21 in the inflammatory milieu leads to T_H3 cell differentiation or T_H17 effector cell differentiation (Zhou et al. 2008; Korn et al. 2007; Veldhoen et al. 2006; Bettelli et al. 2006; Mangan et al. 2006). Therefore, a reciprocal balance between T_H17 cells and T_H3 T_REG cells exists (Bettelli et al. 2006) where IL-6 and IL-21 inhibit T_H3 cell differentiation to the benefit of T_H17 cells (Korn et al. 2009, 2007) and TGF-β elicits T_H3 cell differentiation to the disadvantage of T_H17 cells (Zhou et al. 2008).

Figure 13.

There is a reciprocal relationship between T_H17 (proinflammatory effector T-cell subset that are associated with autoimmune disease) and T_H3 cells (iTREG that are CD4⁺CD25⁺FOXP3⁺), which is elicited during differentiation of naïve T_H0 cells, but final differentiation depends on the cytokine milieu. TGF-β is critical in differentiation of both cell types but depends on the cytokine milieu. The schematic shows the cytokine pathways in the differentiation of T_H17 and T_H3 cells from T_H0 effector cells.

Figure 14.

This schematic focuses on the differentiation pathways of T_H0 to T_H17 and T_H3 cells showing a transitional state (FOXP3⁺, ROR-γt⁺ and RORα⁺ cell) where addition of certain cytokines/factors drives differentiation to T_H3 cells (FOXP3+) leading to suppression or T_H17 cells (ROR-γt⁺ and RORα⁺) resulting in inflammation/autoimmune disease.

Role of T_REG in Mucosal Sites

Oral tolerance is an important mechanism in the mucosal immune system whereby oral administration of a specific antigen induces unresponsiveness of systemic immune responses with the same or different antigens (Chen et al. 2007; Weiner et al. 1994). TGF-β is critical for the induction of oral tolerance (Chen et al. 2007; Weiner et al. 1994). Low-dose of antigen cells leads to “dampening,” a paracrine effect, of the immune response due to TGF-β derived from nT_REG, T_H3, and T_r1 cells. High-dose of an antigen is associated with mucosal T-cell anergy and apoptosis (Chen et al. 2007; Weiner 1997; Weiner et al. 1994). At mucosal sites, T_REG are responsible for “bystander” suppression, where TGF-β produced at mucosal sites during development of oral tolerance regulates immune responses on T-cells, B-cells, NK cells, macrophages, and dendritic cells in an antigen nonspecific manner (Weiner 1997). Animal models of inflammatory bowel disease (IBD) have been used to study T_REG and mucosal tolerance (Blumberg 2009). Researchers have adoptively transferred CD4⁺CD45RB^highT-cells into SCID or Rag-1 mice (Powrie et al. 1994) or have relied on the 2, 4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis rodent model (Te Velde et al. 2006). A negative effect of T_REG in mucosal immunity is the secretion of TGF-β from T_REG in the face of IL-6 and IL-21 in the inflammatory milieu. TGF-β can lead to differentiation of T_H17 cells and subsequent inhibition of T_REG differentiation, resulting in more severe inflammation (Korn et al. 2009, 2007). T_REG have a critical role in tolerance and “bystander” suppression of mucosal sites with resident γδ T-cells.

Role of T_REG in Inflammatory/Infectious Disease

Both natural and induced T_REG are important in suppressing inflammation in infectious disease (Figure 15; Abraham and Medhitzov 2011; Liu et al. 2010; Jager and Kuchroo 2010; Scholzen et al. 2009; de Boer et al. 2007; Belkaid and Rouse 2005). nT_REG are activated by microbial infections and products of the resulting inflammatory milieu. T_REG express toll-like receptors 4, 5, 7, and 8, allowing the cells to respond to bacterial products such as lipopolysaccharide leading to increased T_REG survival and proliferation (Caramahlo et al. 2003). Probiotics have been shown to elicit activation of T_REG, which then suppress T_H1-mediated colitis in the TNBS mouse colitis model (Di Giacinto et al. 2005). Microbes are also able to manipulate antigen-presenting cells leading to priming/activation of T_REG and elicit secretion of chemokines and cytokines that favor induction, priming, recruitment, and survival of T_REG, thus using T_REGfor their own benefit (Cabrera et al. 2004; Hesse et al. 2004; Caramahlo et al. 2003; Belkaid et al. 2002). These microbial organisms include virus (HIV [Aandahl et al. 2004], HCV [Cabrera et al. 2004], CMV [Aandahl et al. 2004], FIV [Vahlenkamp et al. 2004], Herpes simplex virus [Suvas et al. 2004]), bacteria (Helicobacter spp. [Lundgren et al. 2003; Kullberg et al. 2002] and Listeria monocytogenes [Kursar et al. 2002]), fungi (Candida albicans [Montagnoli et al. 2002] and Pneumocystis carinii [Hori et al. 2002]), and protozoal (Leishmania major [Belkaid et al. 2002], Schistosoma mansoni [Hesse et al. 2004] and Plasmodium spp. [Scholzen et al. 2009]). T_REG can become infected with viral pathogens (e.g., HIV and FIV), and it is uncertain if they remain suppressive when infected (Joshi et al. 2004; Oswald-Richter et al. 2004). Animal infection models and infected humans show accumulation of T_REG at the site of infection with leishmaniasis, herpes simplex virus, and schistosomiasis (Hesse et al. 2004; Suvas et al. 2004; Belkaid et al. 2002), in the peripheral blood with HIV and HCV (Oswald-Richter et al. 2004) and in lymphoid organs of HIV patients (Andersson et al. 2005). A good example of the role of T_REG in infection would be Plasmodium spp. that causes malaria in human patients and rodent models and is associated with increased numbers of T_REG (i.e., natural and induced), which have a direct association with the parasitic load in the host. T_REG accumulate in areas of inflammation induced by the organisms and inhibit T_H1 responses (i.e., both protective and pathologic) primarily by the suppressive effects of IL-10 and TGF-β, and ultimately result in either clearance of the organism and resolution or clinical cases of malaria depending on the level of T_REG cell induction and the organism’s manipulation of this lymphocyte population (Scholzen et al. 2009). T_REG has also been shown to be a factor in the development of silica-induced pulmonary fibrosis in a mouse model. Depletion of T_REG leads to the maintenance of a T_H1 response and subsequent attenuation of fibrosis versus the shift to a T_H2 response that normally predisposes to development of fibrosis in this model (Liu et al. 2010). The balance between effector T-cells and T_REG is critical in determining the immune response to pathogens (Figure 16).

Figure 15.

During an infection with a pathogenic organism complex networks develop where nT_REG undergo antigen-specific expansion and T_r1 and iT_REG cells undergo pathogen-specific differentiation in the presence of tolerogenic cytokines (IL-10 and TGF-β). All three types of T_REG cells then work to suppress effector T-cells in the inflammatory milieu by soluble factors, cell-to-cell contact, or competing for IL-2. nT_REG can also induce infectious tolerance in dendritic cells. Together these result in suppression of immune responses to pathogens. Pathogens can also use T_REG for their own benefit to evade the immune response.

Figure 16.

The balance between effector cells and T_REG cells in the inflammatory milieu dictate the course of and ultimate resolution or persistence of the inflammatory response to an infectious agent. There are advantages and disadvantages for both the host and microbe if there is an imbalance in the numbers/function of effector cells and T_REG.

Role of T_REG in Organ Transplantation

T_REG have been shown to have a pivotal role in transplant tolerance leading to graft acceptance and prevention of rejection in xenotransplantation (Muller et al. 2009; Zhang et al. 2009; Le and Chao 2007; Yong et al. 2007). Adoptive transfer of T_REG into mice has been shown to inhibit, delay, and prevent development of graft versus host disease (GVHD) (Taylor et al. 2002; Cohen et al. 2002) as well as to prevent allograft (i.e., pancreatic islet cell transplant) rejection (Battaglia et al. 2006; Gregori et al. 2001). Post-transplant immunosuppressive drugs have been shown to have variable effects on T_REG. Mycophenolate mofetil increases T_REG numbers and induces transplant tolerance when given with vitamin D (Han et al. 2005; Huang et al. 2003; Gregori et al. 2001), calcineurin inhibitors (e.g., cyclosporine, tacrolimus, sirolimus) decrease T_REG and abrogate transplant tolerance (Shoji et al. 2005; Larsen et al. 1996), and Rapamycin and methylprednisolone do not seem to have effects on T_REG or transplant tolerance (Blaha et al. 2003).

Role of T_REGin Pregnancy

Natural T_REG, CD8⁺ T_REG, T_H3 cells, and T_r1 cells have been shown to be important in immune tolerance during pregnancy (Guerin et al. 2009; Trowsdale and Betz 2006; Aluvihare et al. 2004). IL-2/STAT5 signaling and 17-β-estradiol (E2) during pregnancy cause induction of FOXP3 and increased T_REG numbers (i.e., humans and animal models) by induction of FOXP3+ iT_REG and T_REG cell expansion (Fainboim and Arruvito 2011). Fetal alloantigen (Zhao et al. 2007) and placental trophoblast antigens such as heat shock protein-60, carcinoembryonic antigen, CD274 (i.e., ligand for programmed cell death-1 receptor), and human leukocyte antigen-G (Taglauer et al. 2008; Yang et al. 2006; Shao et al. 2005; LeMaoult et al. 2004) are also important in T_REG cell induction/activation and expansion during early pregnancy. Paternal alloantigens and TGF-β in seminal fluid can also induce/activate T_REG (Robertson et al. 2009; Robertson and Sharkey 2001). During the course of pregnancy, there are increased numbers of CD4⁺CD25⁺ cells in the circulation in early pregnancy, reaching an apex during the second trimester and declining until the postpartum period where they reach a number that is nearly at the prepregnancy level (Heikkinen et al. 2004). T_REG are significantly decreased in deciduas from spontaneous vaginal deliveries when compared with Caesarean section, indicating a potential role of declining T_REG in fetal delivery (Xhao et al. 2007; Sindram-Trujillo et al. 2004). The ovary normally contains a population of thymic-derived nT_REG(Samy et al. 2005), and the testis has been shown to have a locally induced iT_REG population that are specifically targeted to testicular antigens and contributes to testicular immune privilege (Nasr et al. 2005). T_REG have been shown to be necessary for immune tolerance of the conceptus, oocytes, and spermatozoa (Trowsdale and Betz 2006). There are increased numbers of T_REG in the blood, decidual tissue, and lymph nodes draining the uterus (Tilburgs et al. 2008; Thuere et al. 2007). T_REG cell depletion and/or decreased function have been shown to lead to loss of pregnancy in rodent models (Aluvihare et al. 2004) and in patients who have miscarried (Yang et al. 2008; Sasaki et al. 2004). Infertility, miscarriage, and pre-eclampsia have been linked with decreased T_REG number and/or function (Guerin et al. 2009; Tilburgs et al. 2008; Thuere et al. 2007; Trowsdale and Betz 2006; Aluvihare et al. 2004).

Role of T_REG in Cancer

T_REG have been shown to dampen the cytotoxic immune response (CD8+/NK cell) as well as suppressing overall level of host immune response to the neoplasm in cancer. Researchers have looked at numbers and location of T_REG and the effects on cancer patient outcome (Menetrier-Caux et al. 2009). They showed that T_REG are present in a large panel of solid tumors in humans. T_REG in pulmonary, pancreatic, gastric, hepatic, and ovarian carcinomas have been correlated with a negative outcome; while in B-cell lymphoma, head and neck cancer and colonic carcinoma T_REG have been associated with a positive patient outcome (Menetrier-Caux et al. 2009). T_REG had no effect on survival with prostatic, renal, and squamous cell carcinomas (Menetrier-Caux et al. 2009). In breast cancer, T_REG in peri-tumoral lymphoid aggregates were correlated with a negative outcome, while intra-tumoral T_REG were associated with a positive outcome. (Menetrier-Caux et al. 2009) The results of vaccine-induced cancer T-cell mediated immunotherapy (i.e., cancer vaccine therapy) have proven to be disappointing (Welters et al. 2008) due to the vaccine’s inability to induce effector T-cells, T_REG already present in the tumor, and/or induction of T_REG by the vaccine itself. Based on these findings, the success of cancer vaccine therapy will depend on the balance between T_REG and effector cells at the start of therapy (Welters et al. 2008). Neoplastic T_REG cells in Sézary Syndrome (leukemic variant of cutaneous T-cell lymphoma in the human) express variant splices of FOXP3. The neoplastic cells with variant FOXP3 are able to function as T_REG and work to dampen the host immune response against the neoplastic T-lymphocytes (Krejsgaard et al. 2008).

T_REG as a Modulatory Target in Drug Development

Pharmacological agents have been developed that control T_REG number and/or function (Ohkura et al. 2011; Nizar et al. 2010; Thorburn and Hansbro 2010; Nandakumar et al. 2009; Tao et al. 2007; Yang et al. 2006). Molecules that increase T_REG number include rTGF-β, FTY720 (Fingolimod, a S1P1 modulator), retinoic acids, histone deacetylase inhibitors, and probiotics. T_REG suppressive function is augmented with the following agents: recombinant IL-2, Rapamycin (mTOR pathway inhibitor) in type-1-diabetes mellitus and renal transplantation, and histone deacetylase inhibitors. Histone deacetylase inhibitors that are also known as chromatin modifying agents (e.g., HDAC9) lead to increased T_REG number and function by a combination of FOXP3 protein acetylation, T_REG chromatin remodeling, and promotion of T_REG development (Tao et al. 2007). While agents that block the TGF-β and/or CTLA-4 signaling pathways decrease T_REGnumber and/or function. Aromatase inhibitors (e.g., Letrozole) used for estrogen modulation in cancer chemotherapy regimens and recombinant IL-2 lead to decreased T_REG numbers.

Biopharmaceutical agents have been developed to modulate T_REG (Khan et al. 2011; Ohkura et al. 2011; De Serres et al. 2011; Weber et al. 2009) including Tremelimumab (CTLA-4 modulation) in advanced melanoma which leads to increased effector T-cell numbers with no change in T_REG number, CD25 modulation by Daclizumab in multiple sclerosis (MS) and advanced breast cancer, Denileukin diftitox as a cancer vaccine, LMB-2 and RFT5-SMPY-dgA in advanced melanoma decrease T_REGnumber, anti-GITR MoAb (DTA1) which leads to decreased T_REG number, agonist anti-OX40 MoAb (OX86) and anti-FR4 MoAb which decrease T_REG number, and Alemtuzumab (anti-CD52 MoAb) which increases T_REG number.

Adoptive transfer of T_REG has been evaluated in clinical trials of patients that have received human stem cell transplants to induce transplant tolerance, patients with GVHD, and type 1 diabetes mellitus patients to ameliorate autoimmune disease with a good patient safety profile and showed that the procedure is feasible, yet efficacy still needs to be shown convincingly (Riley et al. 2009; Trzonkowski et al. 2009).

Conclusions

T_REG have both positive and negative functions in the immune system. Positive aspects of T_REG include suppression of immune responses including autoimmunity, maintaining immune homeostasis, as well as tolerance in xenotransplantation, at mucosal sites, and during pregnancy. Negative aspects of T_REG can include manipulation by some infectious agents to avoid the host’s immune response and in cancer T_REG can suppress the body’s cytotoxic immune response to neoplastic cells. The balance between T_REG and effector cells determines the fate of an immune response. The fact that the immune system has so many sources of regulatory cells which overlap functionally but have slightly different induction/activation pathways underscores the importance of T_REGin host survival.

Footnotes

The author declared no potential conflicts of interests with respect to the authorship and/or publication of this article. The author received no financial support for the research and/or authorship of this article.

Abbreviations

Acknowledgments

I would like to acknowledge the following researchers: Virginia Godfrey, DVM, PhD, DACVP, from the University of North Carolina at Chapel Hill for her kind donation of the “Scurfy” mouse images; Caroline Genell from the GlaxoSmithKline, Safety Assessment, Immunotoxicology Group for the rat T_REG flow cytometry data; and John Spaull of the GlaxoSmithKline MCT Cell Biology Group for the FOXP3 immunofluorescence images.

References

Aandahl

E. M.

Michaelsson

Moretto

W. J.

Hecht

F. M.

Nixon

D. F.

(2004). Human CD4⁺CD25⁺ regulatory T cells control T-cell responses to Human Immunodeficiency Virus and Cytomegalovirus antigens. J Virol 78, 2454–9.

Abraham

Cho

(2009). Interleukin-23/T_H 17 pathways and inflammatory bowel disease. Inflamm Bowel Dis 15(7), 1090–100.

Abraham

Medzhitov

(2011). Interactions between the host innate immune system and microbes in inflammatory bowel disease. Gastroenterol 140, 1729–37.

Akdis

(2009). Immune tolerance in allergy. Curr Opin Immunol 21, 700–7.

Aluvihare

V. R.

Kallikourdis

Betz

A. G.

(2004). Regulatory T cells mediate maternal tolerance to the fetus. Nat Immunol 5, 266–71.

Andersson

Boasso

Nilsson

Zhang

Shire

N. J.

Lindback

Shearer

G. M.

Chougnet

C. A.

(2005). Cutting edge: The prevalence of regulatory T cells in lymphoid tissue is correlated with viral load in HIV-infected patients. J Immunol 174(6), 3143–7.

Annacker

Asseman

Read

Powrie

(2003). Interleukin-10 in the regulation of T cell-induced colitis. J Autoimmun 20, 277–9.

Askenasy

Kaminitz

Yarkoni

(2008). Mechanisms of T regulatory cell function. Autoimmunity Rev 7, 370–5.

Atanackovic

Brunner-Weinzieri

M. C.

Kroger

Serke

Deter

H. C.

(2002). Acute physiological stress simultaneously alters hormone levels, recruitment of lymphocyte subsets, and production of reactive oxygen species. Immunol Invest 31(2), 73–91.

10.

Atanackovic

Schnee

Schuch

Faltz

Schulze

Weber

C. S.

Schafhausen

Bartels

Bokermeyer

Brunner-Weinzieri

M. C.

Deter

H. C.

(2006). Acute physiological stress alerts the adaptive immune response: stress-induced mobilization of effector T cells. J Neuroimmunol 176, 141–52.

11.

Battaglia

Stabilini

Migliavacca

Horejs-Hoeck

Kaupper

Roncarolo

M. G.

(2006). Rapamycin promotes expansion of functional CD4⁺CD25⁺FOXP⁺ regulatory T cells of both healthy subjects and type 1 diabetic patients. J Immunol 177(12), 8338–47.

12.

Beissert

Schwartz

(2006). Regulatory T cells. J Invest Dermatol 126, 15–24.

13.

Belkaid

Piccirillo

A. C.

Mendez

Shevack

Sacks

D. L.

(2002). CD4⁺CD25⁺ regulatory T cells control Leishmania major persistence and immunity. Nature 420, 502–7.

14.

Belkaid

Rouse

B. T.

(2005). Natural regulatory T cells in infectious disease. Nature Immunol 6(4), 353–60.

15.

Bettelli

Carrier

Gao

Korn

Strom

T. B.

(2006). Reciprocal developmental pathways for the generation of pathogenic effector T_H 17 and regulatory T cells. Nature 441, 235–8.

16.

Bienvenu

Martin

Auffray

Cordier

Becourt

Lucas

(2005). Peripheral CD8⁺CD25⁺ T lymphocytes from MHC class II-deficient mice exhibit regulatory activity. J Immunol 175, 246–53.

17.

Biros

(2008). Anterior chamber-associated immune deviation. Vet Clin Small Anim 38, 309–21.

18.

Blaha

Bigenzahn

Koporc

Scmid

Langer

Selzer

(2003). The influence of immunosuppressive drugs on tolerance induction through bone marrow transplantation with costimulation blockade. Blood 101(7), 2886–93.

19.

Bloom

(2006). CD4⁺CD25⁺FOXP3⁺ regulatory T cells in nonhuman primates. Transplant Rev 20, 121–5.

20.

Bluestone

J. A.

Tang

(2005). How do CD4⁺CD25⁺ regulatory T cells control autoimmunity? Curr Opin Immunol 17, 638–42.

21.

Blumberg

R. S.

(2009). Inflammation in the intestinal tract: Pathogenesis and treatment. Dig Dis 27, 455–64.

22.

Brossay

Tangri

Bix

Cardell

Locksley

R. M.

Kronenberg

(1998). Mouse CD1-autoreactive T cells have diverse patterns of reactivity to CD1⁺ targets. J Immunol 160, 3681–8.

23.

Brunkow

M. E.

Jeffery

E. W.

Hjerrild

K. A.

Paeper

Clark

L. B.

Yasayko

S.-A.

Wilkinson

J. E.

Galas

Ziegler

S. F.

Ramsdell

(2001). Disruption of a new forkhead/winged helix protein, scurfin, results in the fatal lymphoproliferative disorder of the Scurfy mouse. Nat Genetics 27, 68–73.

24.

Cabrera

Firpi

R. J.

Rosen

H. R.

Liu

Nelson

D. R.

(2004). An immunomodulatory role for CD4⁺CD25⁺ regulatory T lymphocytes in Hepatitis C Virus infection. Hepatology 40, 1062–71.

25.

Caramahlo

Lopes-Carvahlo

Ostler

Zelenay

Haury

Demengeot

(2003). Regulatory T cells selectively express Toll-Like Receptors and are activated by lipolysaccharide. J Exp Med 197, 403–11.

26.

Chang

C. C.

Ciubotariu

Manavalan

J. S.

(2002). Tolerization of dendritic cells by T(s) cells: The crucial role of inhibitory receptors ILT3 and ILT4. Nature Immunol 3, 237–43.

27.

Chen

Ford

M. S.

Young

K. J.

(2003). Role of double-negative regulatory T cells in long-term cardiax xenograft survival. J Immunol 170, 1846–53.

28.

Chen

Perruche

(2007). CD4⁺CD25⁺ T regulatory cells and TGF-β in mucosal immune system: The good and the bad. Curr Medicinal Chem 14, 2245–9.

29.

Chen

Zhou

Torrealba

J. R.

(2005). Donor lymphocyte infusion induces long-term donor-specific cardiac xenograft survival through activation of recipient double-negative regulatory T cells. J Immunol 175, 3409–16.

30.

Claman

H. N.

Chaperon

E. A.

Triplett

R. F.

(1966). Thymus-marrow cell combinations. Synergism in antibody production. Proc Soc Exp Biol Med 122, 1167–71.

31.

Clark

L. B.

Appleby

M. W.

Brunkow

M. E.

Wilkinson

J. E.

Ziegler

S. F.

Ramsdell

(1999). Cellular and molecular characterization of the Scurfy mouse mutant. J Immunol 162, 2546–54.

32.

Cohen

J. L.

Trenado

Vasey

Klatzmann

Salomon

B. L.

(2002). CD4+CD25+ immunoregulatory T cells: New therapeutics for graft-versus-host disease. J Exp Med 196, 401–6.

33.

Cortesini

LeMaoult

Ciubotariu

Suciu Foca Cortesini

(2001). CD8⁺CD28⁻ T suppressor cells and the induction of antigen-specific, antigen-presenting cell-mediated suppression of T_H reactivity. Immunol Rev 182, 201–6.

34.

Coutinho

Caramalho

Seixas

Demengeot

(2005). Thymic commitment of regulatory T cells is a pathway of TCR-dependent selection that isolates repertoires undergoing positive or negative selection. Curr Top Microbiol Immunol 293, 43–71.

35.

Crome

S. Q.

Wang

A. Y.

Levings

M. K.

(2009). Translational mini-review series on T _H 17 cells: Function and regulation of human T helper 17 cells in health and disease. Clin Exp Immunol 159, 109–19.

36.

Cupedo

Nagasawa

Weijer

Blom

Spits

(2005). Development and activation of regulatory T cells in the human fetus. Eur J Immunol 35, 383–90.

37.

Datta

Sarvetnick

(2009). Lymphocyte proliferation in immune-mediated diseases. Trends Immunol 30(9), 430–8.

38.

Deaglio

. (2007). Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression. J Exp Med 204, 1257–65.

39.

De Boer

O. J.

van der Loos

C. M.

Teeling

van der Wal

A. C.

Teunissen

M. B. M.

(2007). Immunohistocehmical analysis of regulatory T cell markers FOXP3 and GITR on CD4⁺CD25⁺ T cells in normal skin and inflammatory dermatoses. J Histochem and Cytochem 55(9), 891–8.

40.

De Serres

S. A.

Yeung

M. Y.

Mfarrej

B. G.

Najafian

(2011). Effect of biologic agents on regulatory T cells. Transplantation Rev 25(3), 110–6.

41.

Diamond

M. S.

Shrestha

Marri

Mahan

Engle

(2003). B cells and antibody play critical roles in the immediate defense of disseminated infection by West Nile Encephalitis Virus. J Virol 77(4), 2578–86.

42.

Di Giacinto

Marinaro

Sanchez

Strober

Boirivant

(2005). Probiotics ameliorate recurrent T_H 1-mediated murine colitis by inducing IL-10 and IL-10-dependent TGF-β-bearing regulatory cells. J Immunol 174, 3237–46.

43.

Dittel

B. N.

(2008). CD4 T cells: Balancing the coming and going of autoimmune-mediated inflammation in the CNS. Brain, Behavior, and Immunity 22, 421–30.

44.

Fainboim

Arruvito

(2011). Mechanisms involved in the expansion of T_REG during pregnancy: role of IL-2/STAT5 signalling. Journal of Repro Immunol 88, 93–8.

45.

Fontenot

J. D.

Gavin

M. A.

Rudensky

A. Y.

(2003). FOXP3 programs the development and function of CD4⁺CD25⁺ regulatory T-cells. Nat Immunol 4, 330–6.

46.

Fontenot

J. D.

Rudensky

A. Y.

(2005). A well adapted regulatory contrivance: Regulatory T cell development and the forkhead family transcription factor FOXP3. Nature Immunol 6(4), 331–7.

47.

Freir

Weber

C. S.

Nowottne

Horn

Bartels

Meyer

Hildebrandt

Luetkens

Cao

Pabst

Muzzulini

Schnee

Brunner-Weinzieri

M. C.

Marangalo

Bokemeyer

Deter

H.-C.

Atanackovic

(2010). Decrease of CD4⁺FOXP3⁺ T regulatory cells in the peripheral blood of human subjects undergoing a mental stressor. Psychoneuroendocrinol 35, 663–73.

48.

Fujio

Okamura

Yamamoto

(2010). The family of IL-10-secreting CD4⁺T cells. Advances in Immunology 105, 99–129.

49.

Garin

M. I.

. (2007). Galectin-1: A key effector of regulation mediated by CD4⁺CD25⁺ T cells. Blood 109, 2058–65.

50.

Germain

R. N.

(2008). Special regulatory T cell review: A rose by any other name: from suppressor T cells to T_REG, approbation to unbridled enthusiasm. Immunol 123, 20–7.

51.

Godfrey

V. L.

Wilkinson

J. E.

Russell

L. B.

(1991). X-linked lymphoreticular disease in the Scurfy (sf) mutant mouse. Am J Pathol 138(6), 1379–87.

52.

Gregori

Casorati

Amuchastegui

Smiroldo

Davalli

A. M.

Adorini

(2001). Regulatory T cells induced by 1-Alpha-25-Dihydroxyvitamin D3 and Mycophenolate Mofetil treatment mediate transplantation tolerance. J Immunol 167(4), 1945–53.

53.

Greshon

R. K.

Kondo

(1971). Infectious immunological tolerance. Immunology 21, 903–14.

54.

Grossman

W. J.

. (2004). Differential expression of Granzymes A and B in human cytotoxic lymphocyte subsets and T regulatory cells. Blood 104, 2840–8.

55.

Guerin

L. R.

Prins

J. R.

Robertson

S. A.

(2009). Regulatory T-cells and immune tolerance in pregnancy: A new target for infertility treatment? Human Repro Update 15(5), 517–35.

56.

Han

C. H.

H. F.

Wang

Y. X.

Zhang

Wang

Yin

(2005). The influence of Mycophenolate Mofetil upon the maturation and allostimulatory activity of cultured dendritic cell progenitors and the effects of tolerance induction in allograft recipients. Zhonghua YiXue ZaZhi 85(19), 1327–32.

57.

Heikkinen

Mottonen

Alanen

Lassila

(2004). Phenotypic characterization of regulatory T cells in the human decidua. Clin Exp Immunol 136, 373–8.

58.

Hesse

Piccirillo

C. A.

Belkaid

Prufer

Mentink-Kane

Leusink

Cheever

A. W.

Wynn

T. A.

(2004). The pathogenesis of schistosomiasis is controlled by cooperating IL-10-producing innate effector and regulatory T cells. J Immunol 172, 3157–66.

59.

Hezova

Slaby

Faltejskova

Mikulkova

Buresova

Muthu Raja

K. R.

Hodek

Ovesna

Michalek

(2010). MicroRNA-342, microRNA-191, and microRNA-510 are differentially expressed in T regulatory cells of type 1 diabetic patients. Cellular Immunol 260, 70–4.

60.

Hori

Carvahlo

T. L.

Demengeot

(2002). CD25⁺CD4⁺ regulatory T cells suppress CD4⁺ T cell-mediated pulmonary hyperinflammation driven by Pneumocystis carinii in immunodeficient mice. Eur J Immunol 32, 1282–91.

61.

Hori

Nomura

Sakaguchi

(2003). Control of regulatory T cell development by the transcription factor FOXP3. Science 299, 1057–61.

62.

Huang

W. H.

Yan

De Boer

House

A. K.

Bishop

G. A.

(2003). A short course of Mycophenolate immunosuppression inhibits rejection, but not tolerance, of rat liver allografts in association with inhibition of Interleukin-4 and alloantibody responses. Transplantation 76(8), 1159–65.

63.

Ikehara

Yasunami

Kodama

(2000). CD4⁺ Valpha14 natural killer T cells are essential for acceptance of rat islet xenografts in mice. J Clin Invest 105, 1761–7.

64.

Jager

Kuchroo

V. K.

(2010). Effector and regulatory T-cell subsets in autoimmunity and tissue inflammation. Scand J Immunol 72, 173–84.

65.

Jiang

Game

D. S.

Davies

(2005). Activated CD1d-restricted natural killer T cells secrete IL-2: Innate help for CD4⁺CD25⁺ regulatory T cells? Eur J Immunol 35, 1193–200.

66.

Jiang

Zhang

S. I.

Pernis

(1992). Role of CD8⁺ T cells in murine experimental allergic encephalomyelitis. Science 256, 1213–5.

67.

Joetham

. (2007). Naturally occurring lung CD4⁺CD25⁺ T cell regulation of airway allergic responses depends on IL-10 induction of TGF-β. J Immunol 178, 1433–42.

68.

Joshi

Vahlenkamp

T. W.

Garg

Tompkins

W. A. F.

Tompkins

M. B.

(2004). Preferential replication of FIV in activated CD4⁺CD25⁺ T cells independent of cellular proliferation. Virol 321, 307–22.

69.

Kapp

J. A.

Bucy

R. P.

(2008). CD8⁺ suppressor T cells resurrected. Human Immunol 69, 715–20.

70.

Kapp

J. A.

Kapp

L. M.

McKenna

K. C

. (2004 ). γδ T cells play an essential role in several forms of tolerance. Immunol Res 29(1), 93–102.

71.

Kapp

J. A.

(1997). The role of γδ TCR-bearing T cells in oral tolerance. In Proceedings of the 72nd Forum in Immunology: Tolerance and Immunity in the Mucosal Immune System, pp. 561–7.

72.

Kapp

J. A.

(1996). Oral antigen inhibits priming of CD8⁺ CTL, CD4⁺ T cells, and antibody responses while activating CD8⁺ suppressor T cells. J Immunol 156, 916–21.

73.

Pearce

Lake

J. P.

Ziegler

H. K.

Kapp

J. A.

(1997). γδ T lymphocytes regulate the induction and maintenance of oral tolerance. J Immunol 158, 3610–8.

74.

Khan

Burt

D. J.

Ralph

Thistlethwaite

F. C.

Hawkins

R. E.

Elkord

(2011). Tremelimumab (anti-CTLA-4) mediates immune responses mainly by direct activation of T effector cells rather than by affecting T regulatory cells. Clinical Immunol 138, 85–96.

75.

Korn

Bettelli

Gao

Awasthi

Jager

(2007). IL-21 initiates an alternative pathway to induce proinflammatory T_H 17 cells. Nature 448, 484–7.

76.

Korn

Bettelli

Oukka

Kuchroo

V. K.

(2009). IL-17 and T_H 17 cells. Annu Rev Immunol 27, 485–517.

77.

Krejsgaard

Gjerdrum

L. M.

Ralfkiaer

Lauenborg

Eriksen

K. W.

Mathiesen

A.-M.

Bovin

L. F.

Gniadecki

Geisler

Ryder

L. P.

Zhang

Wasik

M. A.

Odum

Woetmann

(2008). Malignant T_REG express low molecular splice forms of FOXP3 in Sézary syndrome. Leukemia 22, 2230–9.

78.

Kronenberg

(1994). Antigens recognized by γδ T cells. Curr Opin Immunol 6, 64–71.

79.

Kullberg

M. C.

Jankovic

Gorelick

P. L.

Caspar

Letterio

J. J.

Cheever

A. W.

Sher

(2002). Bacteria-triggered CD4⁺ T regulatory cells suppress Helicobacter hepaticus-induced colitis. J Exp Med 196, 505–15.

80.

Kuniyasu

Takahashi

Itoh

Shimizu

Toda

Sakaguchi

(2000). Naturally anergic and suppressive CD25⁺CD4⁺ T cells as a functionally and phenotypically distinct immunoregulatory T cell population. Int Immunol 12, 1145–55.

81.

Kursar

Bonhagen

Fensterle

Kohler

Hurwitz

Kamradt

Kaufman

S. H. E.

Mittrucker

H.-W.

(2002). Regulatory CD4⁺CD25⁺T cells restrict memory CD8⁺ T cell responses. J Exp Med 196, 1585–92.

82.

Larsen

C. P.

Elwood

E. T.

Alexander

D. Z.

Ritchie

S. C.

Hendrix

Tucker-Burden

(1996). Long-term acceptance of skin and cardiac allografts after blocking CD40 and CD28 pathways. Nature 381(6581), 434–8.

83.

N. T.

Chao

(2007). Regulating regulatory T cells. Bone Marrow Transplant 39, 1–9.

84.

Lehner

(2008). Special regulatory T cell review: The resurgence of the concept of contrasuppression in immunoregulation. Immunol 123, 40–4.

85.

LeMaoult

Krawice-Radanne

Dausset

Carosella

E. D.

(2004). HLA-GI-expressing antigen presenting cells induce immunosuppressive CD4⁺ T cells. Proc Natl Acad Sci USA 101, 7064–9.

86.

Lenert

Brummel

Field

E. H.

Ashman

R. F.

(2005). TLR-9 activation of marginal zone B cells in lupus mice regulates immunity through increased IL-10 production. J Clin Immunol 25(1), 29.

87.

Greene

M. I.

(2008). Special regulatory T cell review: FOXP3 biochemistry in regulatory T cells—how diverse signals regulate suppression. Immunol 123, 17–9.

88.

Braun

Wei

(2011). Regulatory B cells in autoimmune diseases and mucosal immune homeostasis. Autoimmunity 44(1), 58–68.

89.

Lim

H. W.

Broxmeyer

H. E.

Kim

C. H.

(2006). Regulation of trafficking receptor expression in human forkhead box P3⁺ regulatory T cells. J Immunol 177, 840–51.

90.

Liston

Nutsch

K. M.

Farr

A. G.

Lund

J. M.

Rasmussen

J. P.

Koni

P. A.

Rudensky

A. Y.

(2008). Differentiation of regulatory FOXP3⁺ T cells in the thymic cortex. Proc Nat Acad Sciences 105(33), 11903–8.

91.

Liu

Chen

Song

Chen

(2010). CD4⁺CD25⁺FOXP3⁺ regulatory T cell depletion may attenuate the development of silica-induced lung fibrosis in mice. PLoS ONE 5(11), 1–11.

92.

Lourenco

E. V.

La Cava

(2011). Natural regulatory T cells in autoimmunity. Autoimmunity 44(1), 33–42.

93.

Lundgren

Suri-Payer

Enarsson

Svennerholm

A. M.

Lundin

B. S.

(2003). Helicobacter pylori-specific CD4⁺CD25 high regulatory cells suppress memory T-cell responses to H. pylori in infected individuals. Infect Immun 71, 1755–62.

94.

C. S.

Chew

G. Y. J.

Simpson

(2008). Deficiency of Th17 cells in hyper IgE syndrome due to mutations in STAT3. J Exp Med 205, 1551.

95.

Maggi

Cosmi

Liotta

Romagnani

Annunziato

(2005). Thymic regulatory T cells. Autoimmunity Rev 4, 579–86.

96.

Malek

T. R.

Zhu

Matsutani

Adeegbe

Bayer

A. L.

(2008). IL-2 family of cytokines in T regulatory cell development and homeostasis. J Clin Immunol 28, 635–9.

97.

Mangan

P. R.

Harrington

L. E.

O’Quinn

D. B.

Helms

W. S.

Bullard

D. C.

(2006). Transforming growth factor-β induces development of the T_H 17 lineage. Nature 441, 231–4.

98.

Menetrier-Caux

Gobert

Caux

(2009). Differences in tumor regulatory T-cell localization and activation status impact patient outcome. Cancer Res 69, 7895–8.

99.

Mitchell

G. F.

Miller

J. F.

(1968). Cell to cell interaction in the immune response. II. The source of hemolysin-forming cells in irradiated mice given bone marrow and thymus or thoracic duct lymphocytes. J Exp Med 128, 821–37.

100.

Mizoguchi

Preffer

F. I.

Bhan

A. K.

(2000). Regulatory role of mature B cells in a murine model of inflammatory bowel disease. Int Immunol 12(5), 597–605.

101.

Montagnoli

Bacci

Bozza

Gaziano

Mosci

Sharpe

A. H.

Romani

(2002). B7/CD28-dependent CD4⁺CD25⁺ regulatory T-cells are essential components of the memory-protective immunity to Candida albicans. J Immunol 169, 6298–308.

102.

Mosier

D. E.

(1967). A requirement for two cell types for antibody formation in vitro . Science 158, 1573–5.

103.

Mowat

A. M.

(1994). Oral tolerance and regulation of immunity to dietary antigens. In Handbook of Mucosal Immunology ( Ogra

P. L.

Mestecky

Lamm

M. E.

Strober

McGhee

J. R.

Bienenstock

, eds.), pp. 185–201. Academic Press, San Diego, CA.

104.

Muller

Y. D.

Golshayan

Ehirchiou

Wekerle

Seebach

J. D.

Buhler

L. H.

(2009). T regulatory cells in xenotransplantation. Xenotransplantation 16, 121–8.

105.

Munk

M. E.

Schoel

Modrow

Karr

R. W.

Young

R. A.

Kaufmann

S. H. E.

(1989). T lymphocytes from healthy individuals with specificity to self-epitopes shared by the mycobacterial and human 65-Kilodalton heat shock protein. J Immunol 143, 2844–9.

106.

Nakamura

Sonoda

K. H.

Faunce

D. E.

Gumperz

Yamamura

Miyake

Stein-Streilein

(2003). CD4⁺ NKT cells, but not conventional CD4⁺ T cells, are required to generate efferent CD8⁺ T regulatory cells following antigen inoculation in an immune-privileged site. J Immunol 171, 1266–71.

107.

Nandakumar

Miller

C. W. T.

Kumarguru

(2009). T regulatory cells: An overview and intervention techniques to modulate allergy outcome. Clin Mol Allergy 7, 5–11.

108.

Nasr

I. W.

Wang

Gao

Deng

Diggs

Rothstein

D. M.

Tellides

Lakkis

F. G.

Dai

(2005). Testicular immune privilege promotes transplantation tolerance by altering the balance between memory and regulatory T cells. J Immunol 174, 6161–8.

109.

Niederkorn

J. Y.

(2008). Emerging concepts in CD8⁺ T regulatory cells. Curr Opin Immunol 20, 327–31.

110.

Nistala

Wedderburn

L. R.

(2009). T_H 17 and regulatory T cells: Rebalancing pro- and anti-inflammatory forces in autoimmune arthritis. Rheumatol 48, 602–6.

111.

Nizar

Meyer

Galustian

Kumar

Dalgleish

(2010). T regulatory cells, the evolution of targeted immunotherapy. Biochim Biophys Acta 1806, 7–17.

112.

Ochs

H. D.

Khattri

Bennett

C. L.

Brunkow

M. E.

(2002). Immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome and the Scurfy mutant mouse. Immunol Allergy Clin of North America 22, 357–68.

113.

O’Connor

R. A.

Anderton

S. M.

(2008). FOXP3⁺ regulatory T cells in the control of experimental CNS autoimmune disease. J Neuroimmunol 193, 1–11.

114.

Ohkura

Hamaguchi

Sakaguchi

(2011). FOXP3⁺ regulatory T cells: Control of FOXP3 expression by pharmacological agents. Trends Pharmacol Sci 32(3), 158–66.

115.

Okumura

Takemori

Tokuhisa

Tada

(1977). Specific enrichment of the suppressor T cell bearing I-J determinants: Parallel functional and serological characterizations. J Exp Med 146, 1234–45.

116.

Orihara

Nakae

Pawankar

Saito

(2008). Role of regulatory and proinflammatory T cell populations in allergic diseases. WAO J 1, 9–14.

117.

Oswald-Richter

Grill

S. M.

Shariat

Leelawong

Sundrud

M. S.

Haas

D. W.

Unutmaz

(2004). HIV infection of naturally occurring and genetically reprogrammed human regulatory T-cells. PLOS Biology 2(7), 955–66.

118.

Ozdemir

Akdis

C. A.

(2009). T regulatory cells and their counterparts: Masters of immune regulation. Clin Exp Allergy 39, 626–39.

119.

Pandiyan

Zheng

Ishihara

Reed

Lenardo

M. J.

(2007). CD4⁺CD25⁺FOXP3⁺ regulatory T cells induce cytokine deprivation-mediated apoptosis of effector CD4⁺ T cells. Nature Immunol 8, 1353–62.

120.

Patel

D. D.

(2001). Escape from tolerance in the human X-linked autoimmunity-allergic dysregulation syndrome and the Scurfy mouse. J Clin Invest 107(2), 155–7.

121.

Powrie

Leach

M. W.

Mauze

Menon

Caddle

L. B.

Coffman

R. L.

(1994). Inhibition of T_H1 responses prevents inflammatory bowel disease in SCID mice reconstituted with CD45RB _high CD4⁺ T cells. Immunity 1(7), 553–62.

122.

Quezada

S. A.

Jarvinen

L. Z.

Lind

E. F.

Noelle

R. J.

(2004). CD40/CD154 interactions at the interface of tolerance and immunity. Ann Rev Immunol 22(1), 307–28.

123.

Read

Malstrom

Powrie

(2000). Cytotoxic T lymphocyte-associated antigen-4 plays an essential role in the function of CD25⁺CD4⁺ regulatory cells that control intestinal inflammation. J Exp Med 192, 295–302.

124.

Reigert

Bar-Or

(2008). B-cell-derived Interleukin-10 in autoimmune disease: Regulating the regulators. Nat Rev Immunol 8(6), 486.

125.

Riley

J. L.

June

C. H.

Blazar

B. R.

(2009). Human T regulatory cell therapy: Take a billion or so and call me in the morning. Immunity 30, 656–65.

126.

Robertson

S. A.

Guerin

L. R.

Bromfield

J. J.

Branson

K. M.

Ahistrom

A. C.

Care

A. S.

(2009). Seminal fluid drives expansion of the CD4⁺CD25⁺ T regulatory cell pool and induces tolerance to paternal alloantigens in mice. Biol Reprod 80(5), 1036–45.

127.

Robertson

S. A.

Sharkey

D. J.

(2001). The role of semen in induction of maternal immune tolerance to pregnancy. Semin Immunol 13, 243–54.

128.

Romagnani

Maggi

Liotta

Cosmi

Annunziato

(2009). Properties and origin of human T_H 17 cells. Mol Immunol 47, 3–7.

129.

Roncador

Brown

P. J.

Maestre

Hue

Martinez-Torrecuadrada

J. L.

Ling

K.-L

Pratap

Toms

Fox

B. C.

Cerundolo

Powrie

Banham

A. H.

(2005). Analysis of FOXP3 protein expression in human CD4⁺CD25⁺ regulatory T cells at the single-cell level. Eur J Immunol 35, 1681–91.

130.

Roncarolo

M.-G.

Battaglia

(2007). Regulatory T-cell immunotherapy for tolerance to self antigens and alloantigens in humans. Nature Rev: Immunol 7, 585–98.

131.

Roncarolo

M.-G.

Gregori

Battaglia

Bacchetta

Fleischhauer

Levings

M. K.

(2006). Interleukin-10-secreting type 1 regulatory T cells in rodents and humans. Immunol Rev 212, 28–50.

132.

Sakaguchi

(2005). Naturally arising FOXP3-expressing CD25⁺CD4⁺ regulatory T cells in immunological tolerance to self and non-self. Nature Immunol 6(4), 345–52.

133.

Sakaguchi

Asano

Itoh

Toda

(1995). Immunologic self-tolerance maintained by activated T cells expressing IL-2 recpetor alpha-chains (CD25). Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases. J Immunol 155, 1151–64.

134.

Sakaguchi

Yamaguchi

Nomura

Ono

(2008). Regulatory T cells and immune tolerance. Cell 133, 775–87.

135.

Samy

E. T.

Parker

L. A.

Sharp

C. P.

Tung

K. S. K.

(2005). Continuous control of autoimmune disease by antigen-dependent polyclonal CD4⁺CD25⁺ regulatory T cells in the regional lymph node. J Exp Med 202, 771–81.

136.

Sarris

Andersen

K. G.

Randow

Mayr

Betz

A. G.

(2008). Neuropilin-1 expression on regulatory T cells enhances their interactions with dendritic cells during antigen recognition. Immunity 28, 402–13.

137.

Sasaki

Sakai

Miyazaki

Higuma

Shiozaki

Saito

(2004). Decidual and peripheral blood CD4⁺CD25⁺ regulatory T cells in early pregnancy subjects and spontaneous abortion cases. Mol Hum Reprod 10, 347–53.

138.

Scholzen

Minigo

Plebanski

(2009). Heroes or villains? T regulatory cells in malaria infection. Trends in Parasitol 26 (1), 16–25.

139.

Schwartz

R. H.

(2005). Natural regulatory T cells and self-tolerance. Nature Immunol 6(4), 327–30.

140.

Seo

Tokura

(1999). Downregulation of innate and acquired antitumor immunity by bystander γδ and αβ T lymphocytes with T_H2 or Tr1 cytokine profiles. J Interferon and Cytokine Res 19, 555–61.

141.

Seo

Tokura

Takigawa

Egawa

(1999). Depletion of IL-10 and TGF-β producing regulatory γδ T cells by administering a Daunomycin-conjugated specific monoclonal antibody in early tumor lesions augments the activity of CTLs and NK cells. J Immunol 163, 242–9.

142.

Shalev

Wong

K. M.

Foerster

Zhu

Chan

Maknojia

Zhang

Levy

(2009). The novel CD4⁺CD25⁺ regulatory T-cell effector molecule fibrinogem-like protein-2 contributes to the outcome of murine fulminant viral hepatitis. Hepatology 49(2), 387–97.

143.

Shao

Jacobs

A. R.

Johnson

V. V.

Mayer

(2005). Activation of CD8⁺ regulatory T-cells by human placental trophoblasts. J Immunol 174, 7539–47.

144.

Shevach

E. M.

(2009). Mechanisms of FOXP3⁺ T regulatory cell-mediated suppression. Immunity 30, 636–45.

145.

Shoji

Muniappan

Guenther

D. A.

Wain

J. C.

Houser

S. L.

Hoerbelt

(2005). Long-term acceptance of porcine pulmonary allografts without chronic rejection. Transplant Proc 37(1), 72–4.

146.

Siegmund

Feuerer

Siewert

. (2005). Migration matters: Regulatory T-cell compartmentalization determines suppressive activity in vivo. Blood 106, 3097–104.

147.

Simpson

(2008). Special regulatory T-cell review: Regulation of immune responses-examining the role of T cells. Immunol 123, 13–6.

148.

Sindram-Trujillo

A. P.

Scherjon

S. A.

van Hulst-van Miert

P. P.

Kanhai

H. H.

Roelen

D. L.

Claas

F. H.

(2004). Comparison of decidual leukocytes following spontaneous vaginal delivery and elective caesarean section in uncomplicated human term pregnancy. J Reprod Immunol 62, 125–37.

149.

Strober

Cheng

Zeng

(1996). Double-negative (CD4⁻CD8⁻ alpha beta⁺) T cells which promote tolerance induction and regulate autoimmunity. Immunol Rev 149, 217–30.

150.

Suvas

Azkur

A. K.

Kim

B. S.

Kumaraguru

Rouse

B. T.

(2004). CD4⁺CD25⁺ regulatory T cells control the severity of viral immunoinflammatory lesions. J Immunol 172, 4123–32.

151.

Taglauer

Trikhacheva

A. S.

Slusser

J. G.

Petroff

M. G.

(2008). Expression and function of PDCDI at the human maternal-fetal interface. Biol Reprod 79, 562–9.

152.

Takenoshita

Fukushima

Kumamoto

Iwadate

(2002). The role of TGF-β in digestive organ disease. J Gastroenterol 37(12), 991.

153.

Tang

Krummel

M. F.

(2006). Imaging the function of regulatory T-cells in vivo. Curr Opin Immunol 18, 496–502.

154.

Tao

de Zoeten

E. F.

Ozkaynak

Wang

Greene

M. I.

Wells

A. D.

Hancock

W. W.

(2007). Histone deacetylase inhibitors and transplantation. Curr Opin Immunol 19, 589–95.

155.

Taylor

P. A.

Lees

C. J.

Blazar

B. R.

(2002). The infusion of ex vivo activated and expanded CD4+CD25+ immune regulatory cells inhibits graft-versus-host disease lethality. Blood 99, 3493–9.

156.

Te Velde

A. A.

Verstege

M. I.

Hommes

D. W.

(2006). Critical appraisal of the current practice in murine TNBS-induced colitis. Inflammatory Bowel Diseases 12(10), 995–9.

157.

Thorburn

A. N.

Hansbro

P. M.

(2010). Harnessing regulatory T cells to suppress asthma: From potential to therapy. Am J Respir Cell Mol Biol 43, 511–9.

158.

Thuere

Zenclussen

M. L.

Shumacher

Langwisch

Schulte-Wrede

Teles

Paeschke

Volk

H. D.

Zenclussen

A. C.

(2007). Kinetics of regulatory T cells during murine pregnancy. Am J Reprod Immunol 58, 514–23.

159.

Tian

Zekzer

Hanssen

Olcott

Kaufman

D. L.

(2001). Lipopolysaccharide-activated B cells down-regulate T_H1 immunity and prevent autoimmune diabetes in non-obese diabetic mice. J Immunol 167(2), 1081–9.

160.

Tilburgs

Roelen

D. L.

van der Mast

B. J.

de Groot-Swings

G. M.

Kleijburg

Scherjon

S. A.

Claas

F. H.

(2008). Evidence for a selective migration of fetus-specific CD4⁺CD25 bright regulatory T cells from the peripheral blood to the decidua in human pregnancy. J Immunol 180, 5737–45.

161.

Trentham

D. E.

Townes

A. S.

Kang

A. H.

(1977). Autoimmunity to type II collagen in an experimental model of arthritis. J Exp Med 146(3), 857–68.

162.

Trowsdale

Betz

A. G.

(2006). Mother’s little helpers: Mechanisms of maternal-fetal tolerance. Nat Immunol 7, 241–6.

163.

Trzonkowski

Bieniaszewska

Juscinska

Dobyszuk

Krzystyniak

Marek

Mysliwska

Hellmann

(2009). First-in-man clinical results of the treatment of patients with graft versus host disease with human ex vivo expanded CD4⁺CD25⁺CG127⁻ T regulatory cells. Clinical Immunol 133, 22–6.

164.

Vadas

M. A.

Miller

J. F.

McKenzie

I. F

Chism

S. E.

Shen

F. W.

Boyse

E. A.

Gamble

J. R.

Whitelaw

A. M.

(1976). Ly and Ia antigen phenotypes of T cells involved in delayed-type hypersensitivity and in suppression. J Exp Med 144, 10–9.

165.

Vahlenkamp

T. W.

Tompkins

M. B.

Tompkins

W. A.

(2004). Feline immunodeficiency virus infection phenotypically and functionally activates immunosuppressive CD4⁺CD25⁺T regulatory cells. I Immunol 172, 4752–61.

166.

Veldhoen

Hocking

R. J.

Atkins

C. J.

Locksley

R. M.

Stockinger

(2006). TGF-β in the context of an inflammatory cytokine milieu supports de novo differentiation of IL-17-producing T cells. Immunity 24, 179–89.

167.

Vidovic

Roglic

McKune

Guerder

MacKay

Dembic

(1989). Qa-1 restricted recognition of foreign antigen by a γδ T cell hybridoma. Nature 340, 646–50.

168.

Vignali

D. A. A.

Collison

L. W.

Workman

C. J.

(2008). How regulatory T cells work. Nature Rev Immunol 8, 523–32.

169.

Von Boehmer

(2005). Mechanisms of suppression by suppressor T cells. Nature Immunol 6(4), 338–44.

170.

Wan

Y. Y.

Flavell

R. A.

(2007). “Yin-yang” functions of transforming growth factor-β and T regulatory cells in immune regulation. Immunol Rev 220, 199–213.

171.

Weaver

C. T.

Harrington

L. E.

Mangan

P. R.

Gavriell

Murphy

K. M.

(2006). T_H 17 an effector CD4 T cell lineage with regulatory T cell ties. Immunity 24, 677–88.

172.

Weber

C. A.

Mehta

P. J.

Ardito

Moise

Martin

De Groot

A. S.

(2009). T cell epitope: Friend or foe? Immunogenicity of biologics in context. Adv Drug Delivery Rev 61, 965–76.

173.

Weiner

H. L.

(1997). Oral tolerance: Immune mechanisms and treatment of autoimmune diseases. Immunology Today 18(7), 335–43.

174.

Weiner

H. L.

Friedman

Miller

Khoury

S. J.

al-Sabbagh

Santos

(1994). Oral tolerance: Immunologic mechanisms and treatment of animal and human organ-specific autoimmune disease by oral administration of autoantigens. Ann Rev Immunol 12, 809–37.

175.

Welters

M. J. P.

Piersma

S. J.

van der Burg

S. H.

(2008). T regulatory cells in tumour-specific vaccination strategies. Expert Opin Biol Ther 8(9), 1365–79.

176.

Wirnsberger

Hinterberger

Klein

(2011). Regulatory T-cell differentiation versus clonal deletion of autoreactive thymocytes. Immunol and Cell Biol 89, 45–53.

177.

Wolf

S. D.

Dittel

B. N.

Hardardottir

Janeway

C. A.

(1996). Experimental autoimmune encephalomyelitis induction in genetically B-cell deficient mice. J Exp Med 184(6), 2271–8.

178.

Workman

C. J.

Vignali

D. A. A.

(2004). Negative regulation of T cell homeostasis by LAG-3 (CD223). J Immunol 174, 688–95.

179.

Xhao

J. X.

Zeng

Y. Y.

Liu

(2007). Fetal alloantigen is responsible for the expansion of the CD4⁺CD25⁺ regulatory T cell pool during pregnancy. J Reprod Immunol 75, 71–81.

180.

Yanaba

Bouaziz

J.-D.

Haas

K. M.

Poe

J. C.

Fujimoto

Tedder

T. F.

(2008). A regulatory B cell subset with a unique CD1d hi CD5⁺ phenotype controls T cell-dependent inflammatory responses. Immunity 28(5), 639.

181.

Yang

Qiu

Chen

Lin

(2008). Proportional change of CD4⁺ CD25 + regulatory T cells in decidua and peripheral blood in unexplained recurrent spontaneous abortion patients. Fertil Steril 89, 656–61.

182.

Yang

Luo

(2006). Generation of HSP60-specific regulatory T cells and effect on atherosclerosis. Cell Immunol 243, 90–5.

183.

Yong

Chang

Mei

Y. X.

(2007). Role and mechanisms of CD4 + CD25 + regulatory T cells in the induction and maintenance of transplantation tolerance. Transplant Immunol 17, 120–9.

184.

Zeng

Lewis

Dejbakhsh-Jones

(1999). Bone marrow NK1.1⁻ and NK1.1⁺ T cells reciprocally regulate acute graft versus host disease. J Exp Med 189, 1073–81.

185.

Zhang

G. Y.

Wang

Y. M.

Alexander

S. I.

(2009). FOXP3 as a marker of tolerance induction versus rejection. Curr Opin Organ Transplant 14, 40–5.

186.

Zhang

Z. X.

Wang

(2006). Double-negative T cells, activated by xenoantigen, lyse autologous B and T cells using a perforin/granzyme-dependent, Fas-Fas ligand-independent pathway. J Immunol 177, 6920–9.

187.

Zhao

J. X.

Zeng

Y. Y.

Liu

(2007). Fetal alloantigen is responsible for the expansion of the CD4⁺CD25⁺ regulatory T cell pool during pregnancy. J Reprod Immunol 75, 71–81.

188.

Zhou

Lopes

J. E.

Chong

M. M.

Ivanov

I. I.

Min

(2008). TGF-β-induced FOXP3 inhibits T_H 17 cell differentiation by antagonizing RORγt function. Nature 453, 236–40.

Regulatory T-Cells: Diverse Phenotypes Integral to Immune Homeostasis and Suppression

Abstract

Keywords

Introduction to Regulatory T-Cells

Types of Regulatory T-Cells (TREG, Natural, and Adaptive/Induced) CD4+CD25+ TREG

Adaptive/Induced TREG

Other T-Cells with Regulatory Function

CD4+Vα14+ (NKTREG)

γδ T-Cells (Mucosal/Intraepithelial)

A Non-T Lymphocyte Subset with Regulatory Function

TREG Basics

Effects of Acute and Chronic Stress on Human TREG

Modes of Action of TREG Regulation

TREG Markers (Immunohistochemistry, Flow Cytometry, Intravital Microscopy, and miRNA Analysis)

FOXP3: Function and Biology

FOXP3 Deficiency

The “Scurfy” Mouse

IPEX in Humans

TH17 cells and TREG: A Reciprocal Balance

Role of TREG in Mucosal Sites

Role of TREG in Inflammatory/Infectious Disease

Role of TREG in Organ Transplantation

Role of TREG in Pregnancy

Role of TREG in Cancer

TREG as a Modulatory Target in Drug Development

Conclusions

Footnotes

Abbreviations

Acknowledgments

References

Types of Regulatory T-Cells (T_REG, Natural, and Adaptive/Induced) CD4⁺CD25⁺ T_REG

Adaptive/Induced T_REG

CD4⁺Vα14⁺ (NKT_REG)

T_REG Basics

Effects of Acute and Chronic Stress on Human T_REG

Modes of Action of T_REG Regulation

T_REG Markers (Immunohistochemistry, Flow Cytometry, Intravital Microscopy, and miRNA Analysis)

T_H17 cells and T_REG: A Reciprocal Balance

Role of T_REG in Mucosal Sites

Role of T_REG in Inflammatory/Infectious Disease

Role of T_REG in Organ Transplantation

Role of T_REGin Pregnancy

Role of T_REG in Cancer

T_REG as a Modulatory Target in Drug Development