Member of the immunoglobulin superfamily (IgSF) that links tetraspanin-enriched microdomains to the actin cytoskeleton and plays several important roles in innate and adaptive immunity (PubMed:11504738, PubMed:14662754). Acts as an inducible receptor of HSPA8 on dendritic cells to enhance the CCL21/SLC-dependent migration of activated mature dendritic cells while attenuating their antigen- specific stimulatory capacities (PubMed:17785435). In complex with alpha-actinins ACTN1 and ACTN4, regulates actin dynamics in the immune synapse and subsequent T-cell activation (PubMed:22689882). Inhibits the entry of several viruses such as hepatitis C Virus (HCV) or HIV-1. Mechanistically, promotes a change in CD81 organization at the plasma membrane by significantly restricting its diffusion which in turn influences CD81 interaction with Claudin-1/CLDN1, preventing CLDN1 from acting as a co-receptor required for HCV entry (PubMed:23351194). Accumulates at the presynaptic terminal, the producer cell side of the virological synapse, to prevent HIV-1 Env-mediated cell-cell fusion (PubMed:31757023). Highly expressed on malignant cells with antigen presentation defects, interacts with NK receptor KIR3DL2 to suppress NK-cell cytotoxicity (PubMed:38657602). May participate in the regulation of neurite outgrowth and maintenance of the neural network in the adult brain. {ECO:0000269|PubMed:11504738, ECO:0000269|PubMed:12750295, ECO:0000269|PubMed:12752121, ECO:0000269|PubMed:14662754, ECO:0000269|PubMed:15070678, ECO:0000269|PubMed:17785435, ECO:0000269|PubMed:22689882, ECO:0000269|PubMed:23351194, ECO:0000269|PubMed:31757023}. This is the function of Ensembl gene identifier ENSG00000162729 (IGSF8, immunoglobulin superfamily member 8).