DC-induced CD8.

CD4 T cells are important for CD8 T-cell priming by providing cognate signals for DC maturation. We analyzed the capacity of CD4 T cells to influence CD8 T-cell responses induced by activated DC. Surprisingly, mice depleted for CD4 cells were able to generate stronger antigen-specific CD8 T-cell responses after DC vaccination than non-depleted mice. The same observation was made when mice were vaccinated with MHC class II DC, indicating the presence of a MHC class II-dependent CD4 T-cell population inhibiting CD8 T-cell responses. Recently we described the expansion of DX5CD4 T cells, a T-cell population displaying immune regulatory properties, upon vaccination with DC. Intriguingly, we now observe an inverse correlation between CD8 T-cell induction and expansion of DX5CD4 T cells as the latter cells did not expand after vaccination with MHC class II DC. In vitro, DX5CD4 T cells were able to limit proliferation, modulate cytokine production and induce Foxp3 expression in OVA-specific CD8 T cells. Together, our data show an inhibitory role of CD4 T cells on the induction of CD8 T-cell responses by activated DC and indicate the involvement of DX5CD4, but not CD4CD25, T cells in this process. [ABSTRACT FROM AUTHOR]