IL-20 R alpha (or IL-20 R1) and IL-20 R beta (or IL-20 R2) belong to the class II cytokine receptor family. They form multiple heterodimeric signaling complexes that mediate IL-10 family class II cytokine signals. IL-20 R alpha heterodimerizes with IL-20 R beta to form the functional receptor for IL-19, IL-20 and IL-24. IL-20 R alpha also heterodimerizes with IL-10 R beta to form a functional receptor complex for IL-26, while IL-20 R beta heterodimerizes with IL-22 R to form functional IL-20 and IL-24 receptors. The IL-20 receptors are thought to mediate a number of physiological functions including apoptosis, hematopoiesis, and anti-tumor activities.