Due to the fact, that P. yoelii-infection induce a strong up-regulation of anti-inflammatory IL-10 in both CD4 + CD25 + Foxp3 + Tregs and CD4 + CD25 -Foxp3 -T cells, we analyzed the impact of CD4 + T-cell derived IL-10 in more detail by using the IL-10 fl/fl x CD4cre (CD4IL10-KO) mice.