IL-13 was first cloned in 1993, located on chromosome 5q31, with a length of 1.4kb. It has a mass of 13kDa, folding into 4 α helical bundles. The secondary structure characteristics of IL-13 are similar to Interleukin-4 (IL-4); however, it shares only 25% sequence homology with IL-4 and is able to signal independently from IL-4.
Although mainly associated with the induction of airway diseases, IL-13 also possesses anti-inflammatory properties. IL-13 induces a class of proteolytic enzymes, known as Matrix Metalloproteinases (MMPs), in the airways. These enzymes are required to induce infiltration of inflammatory cells into the airway lumen and then to be cleared there. Among other factors, IL-13 induces these MMPs as part of a mechanism that prevents excessive allergic inflammation leading to suffocation.
The signaling of IL-13 begins with a multi-subunit receptor shared with IL-4. This receptor is a heteromeric receptor complex composed of αIL-4 receptor (IL-4Rα) and αInterleukin-13 receptor (IL-13R1). The high affinity of IL-13 for IL-13R1 leads to their binding, which further increases the possibility of forming heteromeric dimers with IL-4R1 and producing Type 2 IL-4 receptors. Heterodimerization activates STAT6 and IRS.
