Interleukin 13

Interleukin 13 (IL-13) is a protein that in humans is encoded by the IL13 gene. IL-13 was first cloned in 1993 and is located on chromosome 5q31.1 with a length of 1.4kb. It has a mass of 13 kDa and folds into 4 alpha helical bundles. The secondary structural features of IL-13 are similar to that of Interleukin 4 (IL-4); however it only has 25% sequence identity to IL-4 and is capable of IL-4 independent signaling. IL-13 is a cytokine secreted by T helper type 2 (Th2) cells, CD4 cells, natural killer T cell, mast cells, basophils, eosinophils and nuocytes. Interleukin-13 is a central regulator in IgE synthesis, goblet cell hyperplasia, mucus hypersecretion, airway hyperresponsiveness, fibrosis and chitinase up-regulation. It is a mediator of allergic inflammation and different diseases including asthma. IL-13 has effects on immune cells that are similar to those of the closely related cytokine IL-4. However, IL-13 is suspected to be the central mediator of the physiologic changes induced by allergic inflammation in many tissues. Although IL-13 is associated primarily with the induction of airway disease, it also has anti-inflammatory properties. IL-13 induces a class of protein-degrading enzymes, known as matrix metalloproteinases (MMPs), in the airways. These enzymes are required to induce aggression of parenchymal inflammatory cells into the airway lumen, where they are then cleared. Among other factors, IL-13 induces these MMPs as part of a mechanism that protects against excessive allergic inflammation that predisposes to asphyxiation. IL-13 is known to induce changes in hematopoietic cells, but these effects are probably less important than that of IL-4. Furthermore, IL-13 can induce immunoglobulin E (IgE) secretion from activated human B cells. Deletion of IL-13 from mice does not markedly affect either Th2 cell development or antigen-specific IgE responses induced by potent allergens. In comparison, deletion of IL-4 deactivates these responses.