Pathogen-recognition receptor expressed on the surface of immature dendritic cells (DCs) and involved in initiation of primary immune response. Thought to mediate the endocytosis of pathogens which are subsequently degraded in lysosomal compartments. The receptor returns to the cell membrane surface and the pathogen-derived antigens are presented to resting T-cells via MHC class II proteins to initiate the adaptive immune response. On DCs it is a high affinity receptor for ICAM2 and ICAM3 by binding to mannose-like carbohydrates. May act as a DC rolling receptor that mediates transendothelial migration of DC presursors from blood to tissues by binding endothelial ICAM2. Seems to regulate DC-induced T-cell proliferation by binding to ICAM3 on T-cells in the immunological synapse formed between DC and T-cells. (Microbial infection) Acts as an attachment receptor for HIV-1 and HIV-2. (Microbial infection) Acts as an attachment receptor for Ebolavirus. (Microbial infection) Acts as an attachment receptor for Cytomegalovirus. (Microbial infection) Acts as an attachment receptor for HCV. (Microbial infection) Acts as an attachment receptor for Dengue virus. (Microbial infection) Acts as an attachment receptor for Measles virus. (Microbial infection) Acts as an attachment receptor for Herpes simplex virus 1. (Microbial infection) Acts as an attachment receptor for Influenzavirus A. (Microbial infection) Acts as an attachment receptor for SARS-CoV. (Microbial infection) Acts as an attachment receptor for Japanese encephalitis virus. (Microbial infection) Acts as an attachment receptor for Lassa virus (PubMed:23966408). Acts as an attachment receptor for Marburg virusn. (Microbial infection) Acts as an attachment receptor for Respiratory syncytial virus. (Microbial infection) Acts as an attachment receptor for Rift valley fever virus and uukuniemi virus. (Microbial infection) Acts as an attachment receptor for West-nile virus. (Microbial infection) Probably recognizes in a calcium-dependent manner high mannose N-linked oligosaccharides in a variety of bacterial pathogen antigens, including Leishmania pifanoi LPG, Lewis-x antigen in Helicobacter pylori LPS, mannose in Klebsiella pneumonae LPS, di-mannose and tri-mannose in Mycobacterium tuberculosis ManLAM and Lewis-x antigen in Schistosoma mansoni SEA (PubMed:16379498). Recognition of M.tuberculosis by dendritic cells occurs partially via this molecule (PubMed:16092920, PubMed:21203928). Homotetramer. Interacts with C1QBP; the interaction is indicative for a C1q:C1QBP:CD209 signaling complex. Interacts with ICAM2 and ICAM3 by binding to mannose-like carbohydrates. Interacts (via C-type lectin domain) with CEACAM1 (via Lewis X moieties); this interaction is regulated by the glycosylation pattern of CEACAM1 on cell types and regulates contact between dendritic cells and neutrophils (PubMed:16246332). (Microbial infection) Interacts with HIV-1 and HIV-2 gp120 (PubMed:11799126, PubMed:12502850, PubMed:1518869). (Microbial infection) Interacts with ebolavirus envelope glycoproteins (PubMed:12502850, PubMed:12504546). (Microbial infection) Interacts with cytomegalovirus gB protein (PubMed:12433371, PubMed:22496863). (Microbial infection) Interacts with HCV E2 protein (PubMed:15371595, PubMed:16816373). (Microbial infection) Interacts with dengue virus major envelope protein E. (Microbial infection) Interacts with measles hemagglutinin. (Microbial infection) Interacts with herpes simplex virus 1 surface proteins. (Microbial infection) Interacts with Influenzavirus A hemagglutinin. (Microbial infection) Interacts with SARS-CoV spike glycoprotein. (Microbial infection) Interacts with Japanese encephalitis virus E protein. (Microbial infection) Interacts with Lassa virus Glycoprotein. (Microbial infection) Interacts with marburg virus glycoprotein. (Microbial infection) Interacts with Respiratory syncytial virus glycoprotein G. (Microbial infection) Interacts with Rift valley fever virus and uukuniemi virus envelope glycoprotein. (Microbial infection) Interacts with west-nile virus envelope glycoprotein. (Microbial infection) Interacts with whole M.bovis cells in a Ca(2+)-dependent and independent manner; in vitro experiments suggest it interacts with CH60.1 (groL1), DnaK, GADPH (gap) and LrpG (PubMed:21203928). Additional isoforms seem to exist. Several splicing events may be used independently in a modular way. Deletion of the transmembrane domain encoding exon through alternative splicing produces soluble isoforms. Predominantly expressed in dendritic cells and in DC-residing tissues. Also found in placental macrophages, endothelial cells of placental vascular channels, peripheral blood mononuclear cells, and THP-1 monocytes. The tandem repeat domain, also called neck domain, mediates oligomerization. Genetic variations in the CD209 promoter determine M.tuberculosis susceptibility [MIM:607948] (PubMed:16379498). Genetic variations in CD209 may influence susceptibility or resistance to dengue virus infection, as well as disease progression and severity [MIM:614371]. A promoter polymorphism in the CD209 gene is associated with protection from dengue fever, but not dengue hemorrhagic fever. In vitro, is a receptor for HIV-1 and transmits HIV-1 either in trans without DC infection, or in cis following a DC infection to permissive T-cells to induce a robust infection. Bound HIV-1 remains infectious over a prolonged period of time and it is proposed that bound HIV-1 is not degraded but protected in non-lysosomal acidic organelles within the DCs close to the cell membrane thus contributing to the HIV-1 infectious potential during transport by DCs from the periphery to lymphoid organs. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Aberrant splicing. DC-SIGN entry DC-SIGN