IL6 and influenza: The cytokines interferon (IFN)-γ, interleukin (IL)-2, and IL-12 define a T helper 1 (Th1) response that stimulates production of serum immunoglobulin (Ig) G2A and IgG2B Ab in mice [34,35,36,37], whereas the cytokines IL-4, IL-5, IL-6, and IL-10 characterize a Th2 response [38] and stimulate secretion of IgG1, which is the main IgG Ab subclass produced by influenza-infected mice [34].