CD4 and infection: We examined the kinetics of flagellin427–441-specific and SseJ329–341-specific CD4 T cell expansion after intravenous (IV) infection with Salmonella. The pooled secondary lymphoid tissues of a C57BL/6 mouse contained approximately 32 flagellin427–441-specific and 30 SseJ329–341-specific CD4 T cells (Figure 4A).