The main effects of IL-4 are Induction of Th2 cells Stimulation of activated B -, T -, and mast cell proliferation Upregulation of class II MHC molecules on B cells and on macrophages and CD23 on B cells Downregulation of IL-12 production, thereby inhibiting Th1 cell-differentiation Augmentation of macrophage phagocytosis Induction of switch to IgG1 and IgE Clinical relevance of IL-4 includes Involvement of IL-4 (with IL-13) in the production of IgE in atopic allergy For anti-IL-4 receptor mAb, treatment of patients with moderate to severe atopic dermatitis IL-5 is produced by mast cells and Th2 cells.