BTNL9

BTNL9 is expressed in the gastrointestinal epithelium and has recently drawn attention through studies of gut-resident γδ T cell regulation. Work in mouse models shows that butyrophilin-like molecules of this cluster shape the composition and effector state of intestinal T cell populations, and human BTNL9 displays a similar epithelial expression profile, although its cognate receptor remains unidentified. The protein contains two extracellular Ig-like domains and an intracellular B30.2-like domain. As links between metabolite sensing and butyrophilin-like signaling emerge, BTNL9 is increasingly regarded as a candidate regulator of mucosal immune tone.