Interleukin-13 (IL-13) is a 17 kDa immunoregulatory cytokine that plays a key role in the pathogenesis of allergy, cancer, and tissue fibrosis. It is secreted by Th1, Th2, Th17, NK, and mast cells, visceral smooth muscle cells, eosinophils, and basophils. This pattern is similar to the expression of Interleukin-4 (IL-4) but also includes subsets of Th1 and Th17 cells that do not secrete IL-4. IL-13 circulates as a monomer and has two internal disulfide bonds that contribute to its bundled