C-type lectin receptor SIGNR1 expressed on peritoneal phagocytic cells with an immature dendritic cell-like phenotype is involved in uptake of oligomannose-coated liposomes and subsequent cell maturation.

The mannose-binding C-type lectin receptor SIGNR1 appears to be a structural and functional murine homologue of human DC-SIGN, but expression of SIGNR1 and its function in induction of immune responses in dendritic cell (DC) lineages remains unclear. In this study, we demonstrated expression and function of SIGNR1 on mouse peritoneal phagocytic cells with an immature DC-like phenotype. Analysis of these cells with a series of cell lineage markers indicated that CD11b(+)F4/80(-) phagocytic cells expressed costimulatory molecules, the DC marker CD83, and MHC class II, suggesting an immature DC-like phenotype. These immature peritoneal DC-like cells expressed low levels of SIGNR1, in addition to another mannose-binding C-type lectin, CD206. The immature peritoneal DC-like cells ingested oligomannose- or Lewis antigen-coated liposomes in vitro through SIGNR1. Following in vitro uptake of oligomannose-coated liposomes, SIGNR1, but not CD206, disappeared rapidly from the surface of the cells. In response to in vitro uptake of OMLs, the peritoneal DC-like cells matured with increasing expression of CD11c, CD86, and MHC class II. Thus, low levels of SIGNR1 expressed on mouse peritoneal phagocytic cells with an immature DC-like phenotype are primarily involved in uptake of mannose- or fucose-decorated particles, and this uptake leads to cell maturation.