CD4 and infection: At the peak of malaria infection, CD44+ 2W1S-tetramer-positive CD4 T cells demonstrated increased surface expression of PD-1, but not CTLA4 (Fig 5A). Since CD4 T cells are known to express multiple inhibitory molecules during infection with murine malaria parasites [38,39], we determined whether expression of inhibitory molecules was responsible for limiting the effector function of 2W1S-specific T cells after S. Typhimurium vaccination.