B- and T-lymphocyte attenuator (BTLA, CD272) is a transmembrane protein member of the immunoglobulin superfamily, with structural and functional similarities to cytotoxic T-lymphocyte associated protein 4 (CTLA4) and programmed cell death protein 1 (PD1). It is an inhibitory receptor that is involved in downregulation of the immune response. Polymorphisms in the gene may be associated with susceptibility to autoimmune diseases (eg, rheumatoid arthritis), systemic lupus erythematosus, type 1 diabetes mellitus, and cancer. BTLA is expressed in most lymphocytes (high expression in lymph nodes and spleen) and during activation of T cells, remaining expressed on T helper type 1 (Th1) but not Th2 cells. References: Nat Immunol. 2003;4(7):670-679. doi: 10.1038/ni944; Arch Immunol Ther Exp (Warsz). 2015;63(1):73-78. doi: 10.1007/s00005-014-0300-3; Clin Dev Immunol. 2011;2011:305656. doi: 10.1155/2011/305656; Int J Immunogenet. 2009;36(1):65-68. doi: 10.1111/j.1744-313X.2008.00809.x; Breast Cancer Res Treat. 2010;120(1):195-202. doi: 10.1007/s10549-009-0462-6.