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. Probably recognizes in a calcium-dependent manner high mannose N-linked oligosaccharides in a variety of pathogen antigens (By similarity). 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 (By similarity). 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. In vitro, is a receptor for HIV-1, HIV-2 and SIV and transmits viruses to permissive T-cells.