Macrophage-restricted adhesion molecule that mediates sialic- acid dependent binding to lymphocytes, including granulocytes, monocytes, natural killer cells, B-cells and CD8 T-cells. Plays a crucial role in limiting bacterial dissemination by engaging sialylated bacteria to promote effective phagocytosis and antigen presentation for the adaptive immune response (PubMed:12940982, PubMed:33489013). Mediates the uptake of various enveloped viruses via sialic acid recognition and subsequently induces the formation of intracellular compartments filled with virions (VCCs) (PubMed:28129379). In turn, enhances macrophage-to-T-cell transmission of several viruses including HIV-1 or SARS-CoV-2 (PubMed:28129379, PubMed:34782760). Acts as an endocytic receptor mediating clathrin dependent endocytosis. Preferentially binds to alpha-2,3-linked sialic acid (PubMed:12940982). Binds to SPN/CD43 on T-cells (By similarity). May play a role in hemopoiesis. Plays a role in the inhibition of antiviral innate immune by promoting TBK1 degradation via TYROBP and TRIM27-mediated ubiquitination (PubMed:26358190). {ECO:0000250|UniProtKB:Q62230, ECO:0000269|PubMed:12940982, ECO:0000269|PubMed:26358190, ECO:0000269|PubMed:28129379, ECO:0000269|PubMed:33489013, ECO:0000269|PubMed:34782760}. (Microbial infection) Facilitates viral cytoplasmic entry into activated dendritic cells via recognition of sialylated gangliosides pesent on viral membrane. . This is the function of SIGLEC1 (sialic acid binding Ig like lectin 1, ENSG00000088827).