Interleukin 9 receptor (IL9R) also known as CD129 (Cluster of Differentiation 129) is a type I cytokine receptor. IL9R also denotes its human gene. The protein encoded by this gene is a cytokine receptor that specifically mediates the biological effects of interleukin 9 (IL9). The functional IL9 receptor complex requires this protein as well as the interleukin 2 receptor, gamma (IL2RG), a common gamma subunit shared by the receptors of many different cytokines. The ligand binding of this receptor leads to the activation of various JAK kinases and STAT proteins, which connect to different biologic responses.