While splenic naive CD4+ and CD8+ T cells do not express Cyp11a1, upon TCR activation it becomes detectable (Supplementary Figure 6a), in agreement with Mahata et al.46 who reported Cyp11a1 expression after activation selectively in Th2, but not naive, T cells in a helminth infection model. The gene discussed is CD8A; the disease is helminthiasis.