Human LILRB3/CD85a/ILT5 APC-conjugated Antibody

Immunoglobulin-like transcript 5 (ILT5), also known as leukocyte immunoglobulin-like receptor subfamily B (LILRB3), leukocyte immunoglobulin-like receptor 3 (LIR3) and CD85a, is an Ig-like receptor family member that is involved in immune regulation. ILT5 belongs to subfamily B whose members have cytoplasmic tails that contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that inhibit signaling events via phosphatase SHP-1. The counterpart to subfamily B is subfamily A, whose members qualify as activating receptors that lack ITIMs, but signal through association with FcR gamma. ILTs share structural homology and chromosomal localization with the KIR family of receptors (1, 2). Mature ILT5 is a highly polymorphic 85‑95 kDa glycoprotein that consists of a 420 amino acid (aa) extracellular domain (ECD) with four Ig-like domains, a 21 aa transmembrane segment, and a 167 aa cytoplasmic domain with three ITIMs (3, 4). Alternate splicing generates an isoform with a 17 aa insertion in the juxtamembrane ECD. In mouse and rat, the LILRB3 gene encodes the PIR-B protein which has six Ig-like domains. Rodent PIR-B and human ILT5 share 55% aa sequence identity within common regions of their ECDs. Both PIR-B and ILT5 are receptors for S. aureus, and activation of these receptors by bacteria influences the innate immune response triggered by TLRs (4). ILT5 is expressed on the surface of peripheral monocytes, neutrophils, eosinophils, basophils, and mast cell progenitors but not on mature mast cells (5‑7). On basophils, cross-linking of ILT5 to the activating receptors ILT1/LIR7 or Fc epsilonRI inhibits the release of histamine, leukotriene C4, and IL-4 (6). On osteoclast precursors, ILT5 ligation inhibits RANKL or M-CSF induced differentiation (8). ILT5 is down‑regulated on macrophages in rheumatoid arthritis synovial tissue following successful treatment with DMARD anti-rheumatic drugs (9).