Mediates heterophilic cell-cell adhesion which regulates the activation, differentiation and tissue retention of various T-cell subsets (PubMed:15811952, PubMed:18329370, PubMed:19752223, PubMed:24687959). Interaction with CADM1 promotes natural killer (NK) cell cytotoxicity and IFNG/interferon-gamma secretion by CD8+ T-cells in vitro as well as NK cell-mediated rejection of tumors expressing CADM1 in vivo (PubMed:15811952). Regulates CD8+ T-cell proliferation in response to T-cell receptor (TCR) activation (PubMed:18329370). Appears to be dispensable for CD8+ T-cell-mediated cytotoxicity (PubMed:19752223). Interaction with SCRIB promotes the late phase of cellular polarization of a subset of CD4+ T-cells, which in turn regulates TCR-mediated proliferation and IFNG, IL17 and IL22 production (PubMed:18329370). By interacting with CADM1 on CD8+ dendritic cells, regulates the retention of activated CD8+ T-cells within the draining lymph node (PubMed:19752223). Required for the intestinal retention of intraepithelial CD4+ CD8+ T-cells and, to a lesser extent, intraepithelial and lamina propria CD8+ T-cells and CD4+ T-cells (PubMed:24687959). Interaction with CADM1 promotes the adhesion to gut-associated CD103+ dendritic cells, which may facilitate the expression of gut-homing and adhesion molecules on T-cells and the conversion of CD4+ T-cells into CD4+ CD8+ T-cells (PubMed:24687959). Monomer (By similarity). May form homodimer (via Ig-like V-type domain) (By similarity). Interacts (via Ig-like V-type domain) with CADM1 (via Ig-like V-type domain); the interaction competes with CRTAM homodimerization and CADM1 homodimerization (PubMed:15781451, PubMed:15811952). Interacts (via PDZ-binding motif) with SCRIB (via PDZ domain 3); the interaction promotes CRTAM and SCRIB polarization in a subset of CD4+ T-cells (PubMed:18329370). In a subset of CD4+ T-cells, colocalizes with SCRIB at the immunological synapse during the late phase of T-cell activation. In the immune system, expression is restricted to activated class-I MHC-restricted cells, including NKT, NK and CD8+ T-cells (at protein level) (PubMed:10811014, PubMed:15811952, PubMed:18329370, PubMed:19752223). Transiently expressed in activated CD8+ T-cells and a subset of activated CD4+ T-cells (at protein level) (PubMed:18329370). Expressed in activated intestinal T-cells, specifically intraepithelial CD4+ CD8+ T-cells, intraepithelial CD4+ T-cells and, CD8+ T-cells in the intestine epithelium, lamina propria, Peyer's Patches and mesenteric lymph nodes (PubMed:24687959). Also expressed in spleen, brain and testis (PubMed:10811014). The extracellular domain is required for the regulation of IFNG and IL22 production, but is dispensable for late T-cell polarization. No visible phenotype (PubMed:18329370, PubMed:19752223). In the small intestine mucosa and under steady-state conditions, severe reduction in the number of intraepithelial CD4+ CD8+ T-cells and, partial reduction in the number of lamina propria and intraepithelial CD8+ and CD4+ T-cells (PubMed:24687959). In intestinal CD4+ T-cells, expression of gut-retention molecules Itgae/CD103 and Cd69, and gut-homing molecule Ccr9 is reduced (PubMed:24687959). Development of lymphocytes and myeloid cells is normal (PubMed:18329370, PubMed:19752223). However, in older mice, the number of CD4+ and CD8+ T-cells is increased in lymph nodes and blood (PubMed:18329370). Susceptible to oral infection with bacterium C.rodentium resulting in higher bacteria load in the colon and spleen (PubMed:18329370). However, in another study, the mice were not susceptible to oral infection with bacterium C.rodentium (PubMed:24687959). Impaired immune response following intranasal infection with influenza virus caused by a decrease in the number of antigen-specific CD8+ T-cells in the infected lung (PubMed:19752223). However, the capacity of CD8+ T-cells to kill infected cells is not affected (PubMed:19752223). Increased resistance to oral infection with intracellular parasite T.gondii caused by a reduced number of IL17-producing CD4+ T-cells resulting in enhanced clearance of the parasite (PubMed:24687959). Belongs to the nectin family. Truncated N-terminus.