|Detection of SIGNR1/CD209b in Mouse Splenocytes by Flow Cytometry. Mouse splenocytes were stained with Rat Anti-Mouse B220/CD45R APC‑conjugated Monoclonal Antibody (Catalog # FAB1217A) and either (A) Goat Anti-Mouse SIGNR1/CD209b PE‑conjugated Antigen Affinity-purified Polyclonal Antibody (Catalog # FAB1836P) or (B) Normal Goat IgG Phycoerythrin Control (Catalog # IC108P). View our protocol for Staining Membrane-associated Proteins.|
SIGNR1 belongs to the family of C-type lectins that participate in innate immune responses by binding and clearing pathogens (1-3). SIGNR1 is one of four mouse proteins, encoded by separate genes, with significant homology to DC-SIGN and DC-SIGNR (4). Mouse SIGNR1 consists of a 53 amino acid (aa) cytoplasmic domain, a 20 aa transmembrane segment, and a 252 aa extracellular domain that contains a juxtamembrane neck region and a carbohydrate recognition domain (CRD) (4, 5). SIGNR1 is a 50kDa type II protein that forms high molecular weight aggregates as has been shown for DC-SIGN and DC-SIGNR (6, 7). The mouse SIGNR1 mRNA is extensively spliced, giving rise to multiple isoforms in addition to variability in the 5’ and 3’ untranslated regions. The alpha isoform is known as SIGNR1. The beta and gamma isoforms lack the transmembrane segment, with the gamma isoform also showing a 21 aa insertion in the CRD. The δ isoform lacks almost the entire CRD (5). Functional differences between the isoforms have not been described. Within the CRD, mouse SIGNR1 shares 67%-70% aa sequence identity with mouse DC‑SIGN, SIGNR2, 3, and 4, and 64%-68% aa sequence identity with human DC-SIGN, human L-SIGN, and rat DC-SIGN. The CRD binds mannose, GlcNAc, and fucose structures on some bacterial strains, mycobacteria, and yeast (8). SIGNR1 is expressed on macrophages found in the splenic marginal zone, lymph node medulla, and peritoneum (6, 9, 10). It plays a dominant role in the clearance of circulating S. pneumoniae (11-13), enhances TLR4 signaling (14), and cooperates with Dectin-1 in the nonopsonic clearance of fungal pathogens (9, 15). SIGNR1 also binds mouse ICAM-2, human ICAM-2 and -3, and HIV gp120 (10).