|Detection of Human SIRP gamma /CD172g by Western Blot. Western blot shows lysates of NK‑92 human natural killer lymphoma cell line, Jurkat human acute T cell leukemia cell line, and human thymus tissue. PVDF membrane was probed with 0.5 µg/mL of Sheep Anti-Human SIRP gamma /CD172g Antigen Affinity-purified Polyclonal Antibody (Catalog # AF4486) followed by HRP-conjugated Anti-Sheep IgG Secondary Antibody (Catalog # HAF016). Specific bands were detected for SIRP gamma /CD172g at approximately 45-50 kDa (as indicated). This experiment was conducted under reducing conditions and using Immunoblot Buffer Group 1.|
|Detection of SIRP gamma /CD172g in Human Blood Monocytes by Flow Cytometry. Human peripheral blood monocytes were stained with Sheep Anti-Human SIRP gamma /CD172g Antigen Affinity-purified Polyclonal Antibody (Catalog # AF4486) followed by Phycoerythrin-conjugated Anti-Sheep IgG Secondary Antibody (Catalog # F0126) and Mouse Anti-Human CD3 epsilon APC-conjugated Monoclonal Antibody (Catalog # FAB100A). Quadrant markers were set based on control antibody staining (Catalog # 5-001-A).|
Signal regulatory protein gamma (SIRP gamma, designated CD172g), also called SIRP beta 2, 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 beta 1, 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, CD56bright 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 beta 1 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).