CD64 is a 72 kD single chain type I glycoprotein also known as FcγRI and FcRI. CD64 is a member of the immunoglobulin superfamily and is expressed on monocytes/macrophages, dendritic cells, and mast cells. The expression can be upregulated by IFN-γ stimulation. CD64 binds IgG immune complex. It plays a role in antigen capture, phagocytosis of IgG/antigen complexes, and antibody-dependent cellular cytotoxicity (ADCC).
Macrosialin, also known as CD68 and Gp11, is a single-pass type I membrane protein which belongs to theLAMP family. CD68 is highly expressed by blood monocytes and tissue macrophages. It is also expressed in lymphocytes, fibroblasts and endothelial cells. CD68 is expressed in many tumor cell lines which could allow them to attach to selectins on vascular endothelium, facilitating their dissemination to secondary sites. CD68 plays a role in phagocytic activities of tissue macrophages, both in intracellular lysosomal metabolism and extracellular cell-cell and cell-pathogen interactions. It is a commonly used marker for macrophages. However, a number of studies have shown that CD68 antibodies react with other hematopoietic and non-hematopoietic cell types, suggesting that CD68 may not be a macrophage-specific antigen. CD68 binds to tissue- and organ-specific lectins or selectins, allowing homing of macrophage subsets to particular sites. Rapid recirculation of CD68 from endosomes and lysosomes to the plasma membrane may allow macrophages to crawl over selectin-bearing substrates or other cells.
This gene encodes a 110-kD transmembrane glycoprotein that is highly expressed by human monocytes and tissue macrophages. It is a member of the lysosomal/endosomal-associated membrane glycoprotein (LAMP) family. The protein primarily localizes to lysosomes and endosomes with a smaller fraction circulating to the cell surface. It is a type I integral membrane protein with a heavily glycosylated extracellular domain and binds to tissue- and organ-specific lectins or selectins. The protein is also a member of the scavenger receptor family. Scavenger receptors typically function to clear cellular debris, promote phagocytosis, and mediate the recruitment and activation of macrophages. Alternative splicing results in multiple transcripts encoding different isoforms.
CD6 is a member of the group B scavenger receptor cysteine-rich (SRCR) superfamily. CD6 is a type I membrane glycoprotein and contains three extracellular SRCR domains. CD6 is expressed at low levels on immature thymocytes and at high levels on mature thymocytes. The majority of peripheral blood T cells, a subset of B cells, and a subset of neuronal cells express CD6. Mouse CD6 is a 626 amino acid (aa) protein with a 24 aa signal sequence, a 372 aa extracellular domain, and a 204 aa cytoplasmic region. The 668 aa human homolog has also been identified. The human and murine proteins share 70% aa identity over their full lengths. CD6 appears to play a role as both a co-stimulatory molecule in T cell activation and as an adhesion receptor. Studies demonstrating a mitogenic effect for T cells with some CD6 specific monoclonal antibodies, in conjunction with either accessory cells or PMA and anti‑CD2 mAb, support the concept of CD6 as a co-stimulatory molecule. Additionally, anti‑CD6 monoclonal antibody has been used as an immunosuppressive agent for patients undergoing kidney or bone marrow allograft rejection. It has also been used to remove CD6+ T cells from donor bone marrow prior to allogenic bone marrow transplantation. Other studies have demonstrated an adhesive role for CD6, it has been demonstrated to bind the activated leukocyte cell adhesion molecule (ALCAM, CD166). CD6/ALCAM interactions have been postulated to play a role in thymocyte development. Additionally, the presence of ALCAM on neuronal cells may provide a mechanism of interaction between CD6+ T cell and ALCAM+ neuronal cells. Phosphorylation of the CD6 molecule appears to play a role in CD6-mediated signal transduction. Serine and threonine residues become hyperphosphorylated and tyrosine residues become phosphorylated when T cells are activated with anti‑CD6 mAb in conjunction with PMA, anti‑CD2, or anti‑CD3 mAb. The CD6 intracellular domain contains regions that can interact with SH2 or SH3 containing proteins.
CD6, T-cell differentiation antigen, is a cell adhesion molecule that mediates cell-cell contacts and regulates T-cell responses. CD6 functions as costimulatory molecule and promotes T-cell activation and proliferation. CD6 also mediates activation of the inflammatory response and the secretion of pro-inflammatory cytokines in response to LPS.
CD70 is a type II transmembrane glycoprotein and a member of the tumor necrosis factor ligand superfamily (TNFSF), also known as CD27L and TNFSF7. It is normally expressed on medullary thymic epithelial cells. Its expression is induced on activated lymphoid cells (B cells, T cells, and NK cells) and dendritic cells. CD70 is a ligand for CD27, a co-stimulatory receptor that plays an important role in T cell activation and proliferation. CD70 overexpression has been reported in various tumors such as renal cell carcinoma, glioblastoma, and non-small cell lung carcinoma and it’s being actively pursued as a therapeutic target.
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