CD4 and infection: To examine if pathogen-specific Th17 cells are also generated during infection, we intravenously infected C57BL/6 mice with Lm expressing ovalbumin (Lm-Ova) [25], and examined the expression of IL-17 and IFNγ by splenic CD4+ T cells after restimulation with an Lm-specific, MHC II-restricted peptide (listeriolysin O (LLO)190–201).