Human IL-13 Recombinant Protein, eBioscience?. IL-13 is an immunoregulatory cytokine produced primarily by activated Th2 cells, and is involved in regulating inflammatory and immune responses. IL-13 down-regulates macrophage activity, thereby inhibiting the production of pro-inflammatory cytokines and chemokines, and is involved in allergen-induced asthma through mechanisms independent of IgE and eosinophils. IL-13 also regulates several stages of B cell maturation and differentiation, up-regulates CD23 and MHC class II expression, and promotes IgE isotype switching of B cells. Structurally, IL-13 closely resembles IL-3, IL-4, IL-5 and GM-CSF. The gene encoding IL-13, IL3, IL5, IL4, and CSF2 form a cytokine gene cluster on chromosome