Although the mechanisms underlying the association of asthma and viral respiratory tract infection are not completely understood, recent reports indicate that epithelial cell viral infection could produce cytokines, such as IL-33 and IL-25, that interact with allergic inflammation, inducing both antigen-specific and innate TH2 cell–related pathways, and resulting in mucin production, increased TH2 related inflammation, enhanced IL-13, IL-4, and IL-5, and eosinophilia [139,140]. Here, IL4 is linked to asthma.