Abstract
The importance of intratumoral and tumor margin lymphatics was investigated using murine fibrosarcoma and melanoma cell lines overexpressing vascular endothelial growth factor C (VEGF-C), a lymphangiogenic cytokine. Implanted tumors from both cell lines exhibited increased lymphatic metastasis and local invasion in mice but not increased hematogenous lung metastasis relative to control tumors. Immunohistochemical staining with two putative lymphatic markers (LYVE-1 and Prox 1) and an endothelial marker (MECA-32) revealed increased vessels within tumors and at the tumor margins relative to vessels in tumors from cell lines not overexpressing VEGF-C. Vessels within tumors were often collapsed or filled with tumor cells, whereas those at the margin were more normal in appearance. Interstitial fluid pressure was similar within VEGF-C overexpressing fibrosarcomas and control fibrosarcomas, and greater than that of normal tail tissue, suggesting that both tumors lack functional lymphatics. Lymphangiography was performed by three methods (multiphoton laser-scanning microscopy, epifluorescence microscopy, and ferritin microlymphangiography). Functional lymphatics could not be detected at depths of 100 to 400 micrometers or more into VEGF-C overexpressing fibrosarcomas. Functional tumor margin lymphatics were increased in diameter by 26% in VEGF-C overexpressing tumors compared to control tumors. Tumor margin lymphatics were organized similar to those in the normal dermis, indicating they were likely preexisting. These results suggest that tumor margin lymphatics are sufficient for lymphatic metastasis, and the increased metastasis of VEGF-C overexpressing tumors may be due to increased functional lymphatic surface area in the tumor margin.
Padera TP, Kadambi A, di Tomaso E, Carreira CM, Brown EB, Boucher Y, Choi NC, Mathisen D, Wain J, Mark EJ, Munn LL, Jain RK: Lymphatic metastasis in the absence of functional tumor lymphatics. Science 296:1883–1886, 2002
Contributed by Dr. N. L. Stedman, University of Georgia, Athens, GA
Human immunodeficiency virus-1 (HIV-1) has an estimated half-life of only 30 minutes in the circulation, but recent evidence suggests that simian immunodeficiency (SIV) is cleared even more quickly. By injecting radioactively labeled SIV particles into rhesus monkeys, investigators showed that SIV was cleared from the blood with a half-life of 3–4 minutes. This clearance did not appear to be immune-mediated, since the presence of virus-specific antibodies did not alter virus clearance. Most of the virus appeared to be removed in the liver (∼30%), with smaller amounts in the lungs (∼5%) and lymph nodes (∼3%). These findings suggest that virus particles are removed by the reticulendothelial system. Rapid removal of viral particles from the blood by this mechanism may interfere with gene therapy utilizing viral vectors.
Zhang L, Dailey PJ, Gettie A, Blanchard J, Ho DD: The liver is a major organ for clearing simian immunodeficiency virus in rhesus monkeys. J Virol. 76:5271–5273, 2002
As a first step in studying the regional specialization of endothelial cells, a group of international investigators has developed a technique for adoptive transfer of human umbilical vein endothelial cells into immunodeficient mice. Human endothelial cells were suspended in Matrigel and injected subcutaneously into Rag2−/− mice. The fate of the injected cells was determined by immunostaining for human-specific CD31. By 30 days after injection, functional blood vessels composed of human endothelial cells and containing murine erythrocytes had been formed. Transplanted cells recruited pericytes and were responsive to cytokines administered via implanted osmotic pumps. With this technique, human endothelial cells assembled into complex microvessels and these structures remained stable up to 100 days. This technique will be useful for studying vascular remodeling and regulation of the endothelial cell phenotype.
Skovseth DK, Yamanaka T, Brandtzaeg P, Butcher EC, Haraldsen G: Vascular morphogenesis and differentiation after adoptive transfer of human endothelial cells to immunodeficient mice. Am J Pathol 160:1629–1637, 2002
Mycobacterium leprae-induced demyelination contributes to neurologic dysfunction in leprosy patients. In cocultures of Schwann cells and dorsal root ganglion neurons, M. leprae induced significant demyelination within 24 hours of bacterial attachment, and invaded nonmyelinating Schwann cells in large numbers. Ultrastructurally, myelin sheaths had separation of lamellae and formation of myelin ovoids. Affected Schwann cells had no other cytopathic effects. Schwann cell proliferation and axon damage occurred subsequent to demyelination. Similar results were obtained using either gamma-irradiated M. leprae, M. leprae cell wall fraction, or phenolic-glycolipid-1 (PGL-1), the cell wall component of M. leprae likely responsible for demyelination. Viable and irradiated M. leprae and M. leprae cell wall fractions were also injected in the sciatic nerves of Rag1 knockout mice lacking mature B and T lymphocytes and C57BL/6 mice, and produced significant demyelination as early as 24 hours in both without any apparent inflammatory cell infiltrates. These results show that M. leprae induces demyelination by attachment alone and not by an immune-mediated mechanism. Since the bacterium survives in nonmyelinating Schwann cells, the proliferation of these cells following demyelination may provide the bacterium with more cells to infect to help ensure survival in the nervous system.
Rambukkana A, Zanazzi G, Tapinos N, Salzer JL: Contact-dependent demyelination by Mycobacterium leprae in the absence of immune cells. Science 296:927–931, 2002
Contributed by Dr. N. L. Stedman, University of Georgia, Athens, GA
It appears that neural stem cells are widely distributed within the adult nervous system, but neurogenesis in the adult occurs only in the subventricular zone and in the hippocampal subgranular zone. To determine the factors that control neurogenesis in the adult brain, scientists engineered neural stem cells from the hippocampus of a rat to express green fluorescent protein and tracked their development when co-cultered with other cell types. These stem cells had the capacity to differentiate into neurons, oligodendrocytes, or astrocytes both in vivo and in vitro. When neural stem cells were co-cultured with neonatal neurons from the hippocampus, many oligodendrocytes developed. Neural stem cells co-cultured with neonatal astrocytes from the hippocampus, on the other hand, developed mainly into neurons. Further studies showed that adult hippocampal astrocytes also promote neurogenesis, although less effectively than neonatal astrocytes. Astrocytes from the adult spinal cord, however, did not promote neural cell development. Thus it appears the fate of neural stem cells is controlled by the local environment in which they reside.
Song H, Stevens CF, Gage FH: Astroglia induce neurogenesis from adult neural stem cells. Nature 417:39–44, 2002