Th2 cells then mediate the allergic asthma pathway through proinflammatory cytokines—i.e., interleukins (IL)-4, IL-5, IL-9, and IL-13—leading to the production of immunoglobulin E (IgE) early in the cascade and, later, eosinophils (Fig. 1) [47]. Here, IL5 is linked to allergic asthma.