Mouse BTLA Biotinylated Antibody

B- and T-lymphocyte attenuator (BTLA; CD272) is a 70 kDa, Ig-superfamily, type I transmembrane glycoprotein that is structurally similar to the CD28 family of T cell co-stimulatory or coinhibitory molecules (1‑3). Unlike CD28 family members, however, the BTLA extracellular Ig domain is an I-type rather than a V-type domain, and BTLA does not form homodimers (4). BTLA also differs from CD28 family members through the interaction of its Ig domain with the TNF superfamily member HVEM (herpesvirus entry mediator; TNFSF14) rather than with B7 family ligands (5). BTLA is a coinhibitory molecule expressed on T cells, B cells and, depending on the mouse strain, macrophages, dendritic and NK cells (6). Expression is low in naïve T cells and increased during antigen-specific induction of anergy. In B cells, BTLA is highest when cells are mature and naïve (6). BTLA apparently limits T cell numbers, since deletion of BTLA results in overproduction of T cells, especially CD8⁺ memory T cells that are hyper-responsive to TCR crosslinking (7). The 305 amino acid (aa) BTLA contains a 29 aa signal sequence, a 153 aa extracellular domain (ECD), a 21 aa transmembrane sequence, and a 102 aa cytoplasmic domain. There are two ITIM motifs and three Tyr phosphorylation sites in the cytoplasmic tail that mediate inhibitory signaling (8, 9). The binding of the BTLA to HVEM does not preclude additional binding of a mammalian stimulatory HVEM ligand, either LIGHT or lymphotoxin-alpha to the complex (4). At least three alleles varying by up to ten extracellular amino acids occur in different mouse strains (6). The ECD of C57BL/6 BTLA shows 51%, 77% and 40% aa identity to that of human, rat and canine BTLA, respectively. A splice variant lacking the Ig domain, termed BTLAs, has been reported (3).