CD4 and infection: Accordingly, intracellular infections promote IFN-γ and IL-12 production by DCs that activates IFN-γ-producing CD4+ T helper 1 (Th1) and CD8+ cytotoxic T cell responses, whereas extracellular pathogens activate DCs to induce IL-4-producing CD4+ T helper 2 (Th2) cell responses (4, 7).