Lipid tetraspanin-associated transmembrane adapter/mediator that acts as a scaffold for Src-family kinases and other signaling proteins in immune cells (PubMed:21930792). It is involved in major histocompatibility complex class II (MHC-II) signaling transduction in B cells, where it is required in generating the calcium response and enhancing ERK activity upon MHC-II stimulation (PubMed:21930792). In dendritic cells, it is involved in sustaining CLEC7A/DECTIN1 signaling after CLEC7A activation by fungal beta-glucans (By similarity). It also acts as an agonist-inducible signaling adapter for TLR1, TLR2, TLR3, TLR4, and TLR7 by selectively enabling the expression of pro-inflammatory cytokines IL6 and IL12B in macrophages and acting as a scaffold for phosphorylation of Toll-like receptors by Src-family kinases (By similarity). Interacts with CD37, CD53 and CD81 (PubMed:21930792). Interacts (via proline-rich region) with LYN (via SH3 domain) (PubMed:21930792). Interacts with CSK (via SH2 domain); this interaction is dependent on phosphorylation of Tyr-107 (PubMed:21930792). Interacts with BLNK (via SH2 domain); this interaction is dependent on phosphorylation of Tyr-131 (PubMed:21930792). Interacts with GRB2 (via SH2 domain); this interaction may be dependent on phosphorylation of Tyr-69 (By similarity). Interacts with TLR4; this interaction occurs upon lipopolysaccharide activation of TLR4 and is enhanced by phosphorylation of Tyr-107 by LYN (By similarity). This interaction facilitates the phosphorylation of TLR4 by LYN which elicits a selective cytokine response in macrophages (By similarity). Together with MHC-II, associates with lipid-enriched microdomains called tetraspanin-enriched microdomains (TEMs) (PubMed:21930792). Rapidly translocates into immunological synapse (IS) at cell-cell contacts between antigen-presenting cells (APCs) and T-cells (PubMed:21930792). Colocalized with tetraspanins CD37, CD53, and CD81 at the uropod (PubMed:21930792). Present at regions of cell-cell contacts but also at the leading edge of migrating cells (PubMed:21930792). Localizes to phagosomes in dendritic cells after exposure to particulate beta-glucan (By similarity). Expressed in antigen-presenting cells, like peripheral blood leukocytes and monocyte-derived dendritic cells (MDDC) (at protein level) (PubMed:21930792). Highly expressed in lymph nodes and spleen. Expressed in antigen-presenting cells (PubMed:21930792). Faintly expressed in the majority of nonimmune system tissues (PubMed:21930792). Phosphorylated by the Src-family protein tyrosine kinases LYN and SRC (PubMed:21930792). Phosphorylation occurs on tyrosine residues upon MHC-II stimulation (PubMed:21930792). Phosphorylation also occurs on tyrosine residues after activation of CLEC7A/DECTIN1 by particulate beta-glucan (By similarity). Lipopolysaccharide (LPS) induces phosphorylation of Tyr-69, Tyr-107 and Tyr-131 differentially to allow temporal recruitment of effector proteins GRB2, CSK and BLNK (By similarity). Phosphorylation of Tyr-69 is immediately induced by LPS stimulation and allows GRB2 to bind (By similarity). Tyr-107 is phosphorylated 5 minutes after LPS stimulation, which then allows CSK to bind, followed by phosphorylation of Tyr-131 10 minutes after LPS induction, which allows BLNK to bind (By similarity). Phosphorylation at Tyr-107 by LYN occurs after activation of TLR4 by lipopolysaccharide; phosphorylation enhances binding to TLR4 (By similarity). Palmitoylated. It is uncertain whether Met-1 or Met-12 is the initiator.