Human SIRP gamma/CD172g Antibody

Signal regulatory protein gamma (SIRP gamma, designated CD172g), also called SIRP beta2, is a monomeric 45-47 kDa type I transmembrane glycoprotein belonging to the SIRP/SHPS (CD172) family of the Ig superfamily (1 ‑ 5). SIRP members are “paired receptors” with homology in the extracellular domain but variability in the C‑terminus and signaling function (1, 2). The 387 amino acid (aa) SIRP gamma sequence contains a 28 aa potential signal sequence, a 332 aa extracellular domain (ECD) with four potential N‑glycosylation sites, a 23 aa transmembrane domain and a 4 aa cytoplasmic sequence. SIRP gamma contains one V-type Ig‑like domain that contains a J‑like sequence and two C1-type Ig‑like domains within its ECD (1, 2). Isoforms that lack one (isoform 2, 276 aa) or two (isoform 3, 170 aa) membrane-proximal C‑type Ig-like domains have been described (5). Within the ECD, human SIRP gamma isoform 1 shares 78% aa identity with human SIRP beta1, and appears to have structurally similar orthologs only in rhesus monkey and chimpanzee (100% and 91% aa identity, respectively) (2). SIRP gamma is the only SIRP known to be expressed on T cells, CD56^bright NK cells and activated NK cells; it is not expressed on myeloid cells (5, 6). It shows adhesion to CD47, but at lower affinity than SIRP alpha (6). Expression of SIRP gamma on T cells suggests a role as an accessory protein interacting with CD47‑expressing antigen presenting cells (5, 6). Unlike SIRP alpha that has cytoplasmic ITIM domains, and SIRP beta1 that interacts with DAP-12, SIRP gamma does not contain any obvious signaling mechanism (1, 2, 6). However, SIRP gamma-mediated adhesion appears to promote antigen-specific T cell proliferation and costimulate T cell activation (5).