Interleukin 13 (IL-13) is a protein that in humans is encoded by the IL13 gene. IL-13 is located on chromosome 5q31 with a length of 1.4kb. IL-13 and IL-4 exhibit a 30% of sequence similarity and have a similar structure. IL-13 is cytokine secreted by many cell types, but especially T helper type 2 (Th2) cells, which is a mediator of allergic inflammation and disease.

IL-13 specifically induces physiological changes in parasitized organs that are required to expel the offending organisms or their products. For example, expulsion from the gut of a variety of mouse helminths requires IL-13 secreted by Th2 cells. IL-13 induces several changes in the gut that create an environment hostile to the parasite, including enhanced contractions and glycoprotein hyper-secretion from gut epithelial cells, that ultimately lead to detachment of the organism from the gut wall and their removal.