Interleukin-12 Differentially Regulates Expression of IFN-γ and Interleukin-2 in Human T Lymphoblasts

Abstract

Interleukin-12 (IL-12) is known to upregulate expression of interferon-γ (IFN-γ) by activated T cells. However, the effects of IL-12 on production of other Th1-type cytokines are less well defined. In this study, we examined the effects of IL-12 on expression of several cytokines, including IFN-γ, IL-2, tumor necrosis factor-α (TNF-α), and IL-10, by primary human CD3⁺ T cells. Although purified resting T cells were largely nonresponsive to IL-12 stimulation, anti-CD3-activated T cell blasts were strongly responsive, as demonstrated by the ability of IL-12 to induce Stat4 DNA-binding activity. Restimulation of T lymphoblasts on immobilized anti-CD3 monoclonal antibodies (mAb) induced rapid expression of TNF-α mRNA and more gradual increases in mRNA levels for IL-2, IFN-γ, and IL-10. IL-12 markedly upregulated expression of IFN-γ and IL-10 but downregulated expression of IL-2 in a dose-dependent and time-dependent manner. The levels of IL-2 produced by IL-12-treated T cells correlated inversely with the levels of IL-10. Moreover, neutralization of IL-10 activity with anti-IL-10 antibodies normalized IL-2 production by IL-12-treated T cells, confirming that the inhibition of IL-2 production by IL-12 was IL-10 mediated. Thus, IL-12 amplified expression of IFN-γ and IL-10 and, via its ability to upregulate production of IL-10, inhibited expression of IL-2. These findings demonstrate that IL-12 differentially regulates expression of the Th1-type lymphokines, IFN-γ and IL-2, in T lymphoblasts.