CD4 and infection: The induction of IFNγ-producing CD4+ TH1 cells is usually associated with the release of IL-12 which is the main IFNγ-inducing cytokine for T cells and NK cells [73] and it has been shown that efficient immune response against R. typhi in C3H/HeN mice was associated with enhanced serum levels of IL-12 on day 5 post infection [57].