This entry includes CD72 from mammals. Human CD72 is a membrane protein expressed mostly in B cells. It contains a C-type lectin-like domain (CTLD) in the extracellular region and an immunoreceptor tyrosine-based inhibition motif (ITIM) in the cytoplasmic region. It is involved in B-cell proliferation and differentiation []. It plays a role in regulation of the development of systemic lupus erythematosus (SLE), an autoimmune disease characterised by production of autoantibodies to various nuclear components and inflammatory lesions caused by deposition of immune complexes [].
The egg peptide speract receptor is a transmembrane glycoprotein of about500 amino acids []. Topologically, it comprises a large extracellulardomain of about 450 residues, followed by a transmembrane domain and ashort cytoplasmic region of about 12 amino acids. The extracellulardomain contains 4 repeats of a well-conserved region, which spans 115amino acids and contains 6 conserved cysteines. A similar domain is alsofound towards the C terminus of macrophage scavenger receptor type I [],a membrane glycoprotein implicated in the pathologic deposition ofcholesterol in arterial walls during artherogenesis, and in the CD5glycoprotein, which acts as a receptor in regulating T-cell proliferation.The T1/Leu-1/CD5 glycoprotein is expressed at the surface membrane of allmature T cells. It has been implicated both in the proliferative response of activated T cells and in T-cell helper function []. Thecomplete amino-acid sequence of the T1 precursor has been deduced from cDNAclones. The protein contains a classical signal peptide; a 347-residue extracellular segment; a transmembrane region; and a 93-residue intra-cellular segment []. The extracellular region contains several cysteineresidues and comprises 2 speract receptor domains separated by a proline/threonine-rich region []. CD5 has been shown to function as a receptor,delivering co-stimulatory signals to T-cells, interacting specifically withthe cell-surface protein CD72 (Lyb-2 in mice) exclusive to B-cells [].
This entry represents a C-type lectin-like domain (CTLD) of the type found in natural killer cell receptors (NKRs), including proteins similar to oxidized low density lipoprotein (OxLDL) receptor (LOX-1), CD94, CD69, NKG2-A and -D, osteoclast inhibitory lectin (OCIL), dendritic cell-associated C-type lectin-1 (dectin-1), human myeloid inhibitory C-type lectin-like receptor (MICL), mast cell-associated functional antigen (MAFA), killer cell lectin-like receptors: subfamily F, member 1 (KLRF1) and subfamily B, member 1 (KLRB1), and lys49 receptors. CTLD refers to a domain homologous to the carbohydrate-recognition domains (CRDs) of the C-type lectins [].NKRs are variously associated with activation or inhibition of natural killer (NK) cells. Activating NKRs stimulate cytolysis by NK cells of virally infected or transformed cells; inhibitory NKRs block cytolysis upon recognition of markers of healthy self cells. Most Lys49 receptors are inhibitory; some are stimulatory. OCIL inhibits NK cell function via binding to the receptor NKRP1D. Murine OCIL in addition to inhibiting NK cell function inhibits osteoclast differentiation []. MAFA clusters with the type I Fc epsilon receptor (FcepsilonRI) and inhibits the mast cells secretory response to FcepsilonRI stimulus [, ]. CD72 is a regulator of B cell receptor signaling []. NKG2D is an activating receptor for stress-induced antigens; human NKG2D ligands include the stress induced MHC-I homologs, MICA, MICB, and ULBP family of glycoproteins. Several NKRs have a carbohydrate-binding capacity which is not mediated through calcium ions (e.g. OCIL binds a range of high molecular weight sulfated glycosaminoglycans including dextran sulfate, fucoidan, and gamma-carrageenan sugars) []. Dectin-1 binds fungal beta-glucans and is involved in the innate immune responses to fungal pathogens [, ]. MAFA binds saccharides having terminal alpha-D mannose residues in a calcium-dependent manner. LOX-1 is the major receptor for OxLDL in endothelial cells and thought to play a role in the pathology of atherosclerosis []. Some NKRs exist as homodimers (e.g.Lys49, NKG2D, CD69, LOX-1) and some as heterodimers (e.g. CD94/NKG2A). Dectin-1 can function as a monomer in vitro.
