Production of T-helper type 1 (Th1) cytokines such as IFN-γ, TNF-α/β, IL-2, IL-3, and IL-12 have been implicated in viral clearance or resistance to infection, while production of Th2 cytokines such as IL-4, IL-5, IL-13, IL-6, and IL-10 cytokines is associated with progression of the infection or viral persistence [23–28]. This evidence concerns the gene IL4 and infection.