CD4 and infection: In parallel, the frequency of IL-17-producing cells among adoptively transferred Ova-TCR+CD4+ T cells, albeit being at a low level, was significantly higher upon infection with Yptb-WT when compared to uninfected controls (Fig. 1c), in line with a significant increase in IL-17-producing endogenous CD4+ T cells at day 8 p.i. (Supplementary Fig. S1).