CD4 and infection: Lastly, in contrast to Tnfrsf4Cre/+R26+/+ and B6 mice, which effectively cleared experimental infection with Pneumocystis murina, Tnfrsf4Cre/+R26Dta/+ mice remained persistently infected and failed to thrive, with susceptibility intermediate between T cell-replete and MHC II-deficient mice, which lacked CD4+ T cells (Figure 5d).