Polarization of Naive CD4+ T Cells Toward the Th1 Subset by CTLA-4 Costimulation

In this study, we examined in vitro the role of CTLA-4 costimulation in the polarization of naive CD4+ T cells toward the Th1 subset. When CTLA-4 costimulation was blocked by the inclusion of anti-CTLA-4 Fab in cultures during priming of naive CD4+ T cells with anti-CD3 in the presence of splenic adherent cells, they were polarized toward the Th2 subset. Conversely, the engagement of CTLA-4 with immobilized anti-CTLA-4 or with CD80-P815 cells polarized naive CD4+ T cells costimulated with anti-CD3 and anti-CD28 toward the Th1 subset. The CTLA-4 costimulation during priming augmented TGF-beta1 mRNA accumulation in naive CD4+ T cells, and the inclusion of anti-TGF-beta in cultures for priming suppressed the effect of CTLA-4 costimulation on the Th1 polarization. The addition of low doses of TGF-beta1 in cultures for priming of naive CD4+ T cells enhanced the production of Th1 cytokines upon secondary stimulation, although Th2 cytokine production was not affected by the doses of TGF-beta1. The CTLA-4 costimulation was also shown to suppress IL-4 production of naive CD4+ T cells upon priming. These results indicate that the costimulation against CTLA-4 drives polarization of naive CD4+ T cells toward the Th1 subset independent of IL-12 through, at least in part, the enhancement of TGF-beta1 production, and it also hampers Th2 subset differentiation by affecting IL-4 production of naive CD4+ T cells.