Interleukin 12 and B7/CD28 interaction synergistically upregulate interleukin 10 production by human T cells

Interleukin 12 (IL-12) is a heterodimeric cytokine which promotes the development of Th1 cells and their interferon gamma (IFN-gamma) production after TCR/CD3 triggering. Previous reports indicate that IL-12 synergizes with accessory signalling through B7/CD28 interaction in inducing proliferation and IFN-gamma production by human T cells. In this study, we investigated the capacity of IL-12 to modify cytokine synthesis by freshly purified human peripheral blood T cells stimulated with anti-CD3 as the primary signal and with CD80 on transfected mouse cells as an accessory signal. Our data demonstrate that IL-12 indeed synergizes with B7/CD28 interaction, not only in inducing IFN-gamma production, but also in enhancing IL-10 synthesis in a dose-dependent manner. In contrast, IL-4 and IL-5 production were slightly inhibited by IL-12. The effect of IL-12 on the secretion of IL-10 was confirmed by stimulating T cells in the absence of accessory cells with immobilized anti-CD3 mAb and soluble anti-CD28 mAb. CD80 and IL-12 mainly costimulated CD4+CD45RO+ T cells but not CD8+ or CD45RA+ T cells to produce IL-10. Cyclosporin A (CsA) partially inhibited, and a neutralizing anti-IL-2 mAb in combination with anti-IL-2R mAbs (anti-Tac and Mik beta1) strongly reduced IL-10 production. On the other hand, IL-12 did not affect IL-2 production. The data thus suggest a model in which optimal IL-10 production by stimulated peripheral blood T cells results from the co-operation of IL-12, B7/CD28 interaction and the ensuing IL-2 activity.