IL-4 is a cytokine secreted by type II helper T cells (Th2 cells).IL-4 is a pleiotropic cytokine that plays an important role in regulating the proliferation, differentiation, and apoptosis of T, B, and other types of cells, and promotes the immune response characterized by Th2 cells.The multiple biological effects of IL-4 are dependent on the type of cell and the state of differentiation, and studies have shown that IL-4 has multiple roles in mediating immune responses to allergic diseases, autoimmune diseases, infectious diseases, and tumors. Studies have shown that IL-4 has multiple roles in mediating immune responses to allergic diseases, autoimmune diseases, infectious diseases, tumors and other diseases, and has therapeutic effects on tumors, autoimmune diseases and infectious diseases, and that IL-4 has a regulatory effect on vaccine immune responses.