Background：

This gene is a member of the immunoglobulin superfamily and encodes a protein which transmits an inhibitory signal to T cells. The protein contains a V domain， a transmembrane domain， and a cytoplasmic tail. Alternate transcriptional splice variants， encoding different isoforms， have been characterized. The membrane-bound isoform functions as a homodimer interconnected by a disulfide bond， while the soluble isoform functions as a monomer. Mutations in this gene have been associated with insulin-dependent diabetes mellitus， Graves disease， Hashimoto thyroiditis， celiac disease， systemic lupus erythematosus， thyroid-associated orbitopathy， and other autoimmune diseases.