CD4+ Th1 cells producing IFN-γ, IL-2, and TNF-α are responsible for cell-mediated immune responses such as delayed type hypersensitivity and tissue injury in infections and autoimmune diseases, whereas CD4+ Th2 cells that produce IL-4, IL-5, IL-6, IL-10, and IL-13 are associated with Ab production by B cells. This evidence concerns the gene IL2 and infection.