signr-1

The cluster of differentiation (CD) system is commonly used as cell markers in Immunophenotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules associating with the immune function of the cell. There are more than 320 CD unique clusters and subclusters have been identified. Some of the CD molecules serve as receptors or ligands important to the cell through initiating a signal cascade which then alter the behavior of the cell. Some CD proteins do not take part in cell signal process but have other functions such as cell adhesion. CD209b, also known as SIGNR1, is a C-type lectin receptor. CD209b is present on most regions of mouse brain and found on microglia and dendritic cells but not on neurons or astrocytes. CD209b is implicated in the recently described SIGNR1 complement activation pathway, which operates against capsular polysaccharides in splenic marginal macrophages. CD209b in rat is homologue to SIGNR1 in mouse, both of which are found to mediate the uptake of dextran or CPS14 within the splenic marginal zone.

CD299 is also known as DC-SIGNR and CLEC4M, is a type II integral membrane protein. DC-SIGNR exists as a homotetramer, and the tandem repeat domain, also called neck domain, mediates oligermerization. Multiple human DC-SIGN/CD209 splice forms exist, generating both membrane-bound and soluble forms. DC-SIGNR is ragarded as a pathogen-recognition receptor involved in peripheral immune surveillance in liver, and probably mediate the endocytosis of pathogens which are subsequently degraded in lysosomal compartments. DC-SIGNR appears to selectively recognize and bind many viral surface glycoproteins containing high mannose N-linked oligosaccharides in a calcium-dependent manner, including HIV-1 gp12, HIV-2 gp12, SIV gp12, ebolavirus glycoproteins, HCV E2, and human SARS coronavirus protein S, as well as the cellular adhesion protein ICAM3. DC-SIGN/CD209 is expressed on dendritic cells (DC) and inflammatory macrophages and contributes to antigen presentation.