Interleukin 4 (IL-4) is a cytokine, which is multifunctional. It can regulate differentiation, proliferation and apoptosis. What is most important it participates in the Th0 differentiation to Th2 cells, which is part of the regulation of the immune system. IL-4 is maturing and endurance element for lymphocytes. It is able to protect lymphoid cells from apoptosis, a process of arranged cell death. The problem of this is that the cytokine is incapable to stimulate the proliferation of the little lymphocytes in rest, without the use of co-stimulatory sign by the antigen receptor connection. The aftermath of IL-4 is not limited to lymphoid cells. In comparison to allergic disorders, autoimmune disorders are affected by Th1 and monocytic cytokines. In this way, IL-4 is working as antiinflammatory cytokine in these disorders as tested on Laboratory rats models for Rheumatoid Arthritis
and Diabetes. Interleukin 4 is mostly related to Interleukin 13, because it has similiar functions and shares the same receptors.