IL13 is an immunoregulatory cytokine produced primarily by activated Th2 cells. IL-13 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. This gene，IL3，IL5，IL4，and CSF2 form a cytokine gene cluster on chromosome 5q，with this gene particularly close to IL4.
