Interleukin-13 is also known as IL-13. It is a protein that in humans is encoded by the IL13 gene. Interleukin-13 is an immunoregulatory cytokine produced primarily by activated Th2 cells.It is involved in several stages of B-cell maturation and differentiation. It up-regulates CD23 and MHC class II expression, and promotes IgE isotype switching of B cells. This cytokine down-regulates macrophage activity, thereby inhibits the production of pro-inflammatory cytokines and chemokines. This cytokine is found to be critical to the pathogenesis of allergen-induced asthma but operates through mechanisms independent of IgE and eosinophils.