Butyrophilin 1A1 (BTN1A1) is a B7-related protein in a family that may show co-stimulatory/inhibitory function. BTN1A1 binds to xanthine oxidoreductase (XOR) and is essential in the control of milk fat globule secretion. The B30.2 domain of butyrophilins can sense changes in intracellular phopho-antigen (pAg) concentrations. Its binding to pAg leads to gamma-delta T cell activation. BTN1A1 inhibits CD4+ T cell proliferation and reduces IL-2 and IFN-gamma expression. BTN1A1 has a protective effect against the development of experimental autoimmune encephalomyelitis (EAE).