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The T1/Leu1/CD5 molecule, a human T-cell surface glycoprotein of relative molecular mass (Mr) 67,000, has been implicated in the proliferative response of activated T cells and in T-cell helper function. Ly1 is the murine homolog. (In the mouse, lymphocyte surface antigens that are markers for function have been identified. Allelic forms are known and chromosomal assignment of the loci has been achieved. Ly1 is on mouse chromosome 19. Ly2 and Ly3 are on mouse chromosome 6. Ly5 is on mouse chromosome 1. Ly6 is on mouse chromosome 15.

CD8 is a cell surface glycoprotein found on most cytotoxic T lymphocytes that mediates efficient cell-cell interactions within the immune system. CD8 acts as a co-receptor, and the T-cell receptor on the T lymphocyte recognize antigen displayed by an antigen presenting cell (APC) in the context of class I MHC molecules. The functional CD8 is either a homodimer composed of two alpha chains, or a heterodimer composed of one alpha and one beta chain. Both alpha and beta chains share significant homology to immunoglobulin variable light chains.
CD8 identifies cytotoxic/suppressor t-cells that interact with MHC class I bearing targets. CD8 is thought to play a role in the process of t-cell mediated killing. CD8 alpha chains binds to class-I MHC molecules alpha-3 domains.

CD3 has four peptide chains (gamma, delta, epsilon and zeta) that form CD3. Defects in CD3 are associated with T cell immunodeficiency CD3 complex mediates signal transduction.

CD4 is a cell-surface glycoprotein found on the mature helper T cells and immature thymocytes, as well as on monocytes and macrophages. (Some cytotoxic T cells have CD4 protein as well.) Normally, about 65% of T cells in the blood are CD4+ (have CD4 protein protruding from their membrane). A mature T cell with either have CD4 or CD8, but not both. During one stage of development T cells develop CD4 and CD8 receptors, but they eventually are differentiated in the thymus and become more specialized.

CD3-epsilonpolypeptide (CD3E) along with CD3-gamma, -delta and -zeta, and the T-cell receptor alpha/beta and gamma/delta heterodimers, creates the T-cell receptor-CD3 complex. This complex has an imperative role in coupling antigen recognition to a number of intracellular signal-transduction pathways. The genes encoding the epsilon, gamma delta polypeptides are found in the same cluster on chromosome 11. The epsilon polypeptide plays a vital role in T-cell development. CD3E gene defects cause immunodeficiency. CD3E is also linked to a susceptibility to type I diabetes in women.

CD1a is a transmembrane glycoproteins, which is structurally related to the major histocompatibility complex (MHC) proteins and form heterodimers with beta-2-microglobulin. CD1a mediates the presentation of primarily lipid and glycolipid antigens of self or microbial origin to T cells. The human genome contains five CD1 family genes organized in a cluster on chromosome 1. The CD1 family members are thought to differ in their cellular localization and specificity for particular lipid ligands. The protein encoded by this gene localizes to the plasma membrane and to recycling vesicles of the early endocytic system. Alternatively spliced transcript variants have been observed, but their biological validity has not been determined.

CD45 leukocyte common antigen (LCA) belongs to the family of at least four isoforms of membrane glycoproteins (220, 205, 190, 180kDa) expressed on hematopoietic cell lines but absent on non-hematopoietic cell lines, normal and malignant non-hematopoietic tissues. The intracellular portion of these molecules has protein phosphatase activity and is involved in regulation of transmembrane signals.

CD57 also called B3GAT1is part of the glucuronyltransferase gene family. CD57 exhibits strict acceptor specificity, recognizing nonreducing terminal sugars and their anomeric linkages. CD57 takes part in the glucuronyl transfer reaction during the biosynthesis of the carbohydrate epitope HNK-1.

CD44 is a cell-surface glycoprotein that plays a role in cell-cell interactions, cell adhesion and migration. CD44 is a receptor for hyaluronic acid and also interacts with other ligands, such as osteopontin, collagens, and matrix metalloproteinases. CD44 participates in a wide variety of cellular functions such as lymphocyte activation, recirculation and homing, hematopoiesis, and tumor metastasis. CD44 and CD49d are putative activity markers and CD44 a potential novel therapeutic target in multiple sclerosis. Increased CD44 antigen is associated with relapses in non-small cell lung cancers.

CD3 has four peptide chains (gamma, delta, epsilon and zeta) that form CD3. Defects in CD3 are associated with T cell immunodeficiency CD3 complex mediates signal transduction.

CD40 is part of the TNF-receptor superfamily. CD40 is a necessary mediator for vast range of immune and inflammatory responses together with T cell-dependent immunoglobulin class switching, memory B cell growth, and germinal center formation. The transcription factor AKNA regulates the expression of CD40 and its ligand, which is vital for homotypic cell interactions. Adaptor protein TNFR2 interacts with CD40 and serves as a mediator of the signal transduction. The interaction of CD40 and its ligand is crucial for amyloid-beta-induced microglial activation, and thus is thought to be an early event in Alzheimer disease pathogenesis. CD40 is the receptor for TNFSF5/CD40L.

CD31 is a glycoprotein expressed on endothelial cells, platelets, macrophages and Kupffer cells, granulocytes, T / NK cells, lymphocytes, megakaryocytes, fibroblasts, osteoclasts, neutrophils. In humans, the gene encoding CD31 is found on chromosome 17.
CD31 is a cluster of differentiation molecule. It is also called PECAM-1 for platelet endothelial cell adhesion molecule. It plays a key role in removing aged neutrophils from the body. Both the neutrophil and the macrophage express CD31 on their membranes, and during the testing process, these CD31 molecules bind the two cells together. If the neutrophil is healthy, it will send a signal to the macrophage, and the CD31 molecules will detach.
CD31 is also expressed in certain tumors, including epithelioid hemangioendothelioma, epithelioid sarcoma-like hemangioendothelioma, other vascular tumors, histiocytic malignancies, and plasmacytomas. It is rarely found in some sarcomas and carcinomas.

CD34 is a single chain transmembrane glycoprotein which is selectively expressed on human lymphoid and myeloid hemapoietic progenitor cells. CD34 has been used to measure angiogenesis, which reportedly predicts tumor recurrence.

CD4 is a cell-surface glycoprotein found on the mature helper T cells and immature thymocytes, as well as on monocytes and macrophages. (Some cytotoxic T cells have CD4 protein as well.) Normally, about 65% of T cells in the blood are CD4+ (have CD4 protein protruding from their membrane). A mature T cell with either have CD4 or CD8, but not both. During one stage of development T cells develop CD4 and CD8 receptors, but they eventually are differentiated in the thymus and become more specialized.

CD58 is part of the immunoglobulin superfamily. CD58 is a ligand of the T lymphocyte CD2 protein, and is invloved in adhesion and activation of T lymphocytes. CD58 is localized to the plasma membrane.

CD44 is a cell-surface glycoprotein that plays a role in cell-cell interactions, cell adhesion and migration. CD44 is a receptor for hyaluronic acid and also interacts with other ligands, such as osteopontin, collagens, and matrix metalloproteinases. CD44 participates in a wide variety of cellular functions such as lymphocyte activation, recirculation and homing, hematopoiesis, and tumor metastasis. CD44 and CD49d are putative activity markers and CD44 a potential novel therapeutic target in multiple sclerosis. Increased CD44 antigen is associated with relapses in non-small cell lung cancers.

CD44 is a cell-surface glycoprotein that plays a role in cell-cell interactions, cell adhesion and migration. CD44 is a receptor for hyaluronic acid and also interacts with other ligands, such as osteopontin, collagens, and matrix metalloproteinases. CD44 participates in a wide variety of cellular functions such as lymphocyte activation, recirculation and homing, hematopoiesis, and tumor metastasis. CD44 and CD49d are putative activity markers and CD44 a potential novel therapeutic target in multiple sclerosis. Increased CD44 antigen is associated with relapses in non-small cell lung cancers.

CD4 is a cell-surface glycoprotein found on the mature helper T cells and immature thymocytes, as well as on monocytes and macrophages. (Some cytotoxic T cells have CD4 protein as well.) Normally, about 65% of T cells in the blood are CD4+ (have CD4 protein protruding from their membrane). A mature T cell with either have CD4 or CD8, but not both. During one stage of development T cells develop CD4 and CD8 receptors, but they eventually are differentiated in the thymus and become more specialized.

Membrane cofactor protein isoform 14 (CD46), is a type I membrane protein which has cofactor activity for inactivation of complement components C3b and C4b by serum factor I. This function resides in the complement control protein repeats (CCPs), with CCP1–4 vital for regulation. CD46 is also involved in the fusion of the spermatozoa with the oocyte during fertilization. CD46 is common in thymocytes, T cells, B cells, monocytes, granulocytes, NK cells, platelets, endothelial cells, epithelial cells, fibroblasts, placenta and sperm.

CD57 also called B3GAT1is part of the glucuronyltransferase gene family. CD57 exhibits strict acceptor specificity, recognizing nonreducing terminal sugars and their anomeric linkages. CD57 takes part in the glucuronyl transfer reaction during the biosynthesis of the carbohydrate epitope HNK-1.

E-Selectin belongs to a family of divalent cation-dependent carbohydrate-binding glycoproteins or adhesion molecules. CD62E is expressed on the surface of endothelial cells and mediates the interaction of leukocytes and platelets with endothelial cells during an inflammatory response. CD62E is found in cytokine-stimulated endothelial cells and is accountable for the accumulation of blood leukocytes at sites of inflammation by mediating the adhesion of cells to the vascular lining. It demonstrates structural features such as the existence of lectin- and EGF-like domains followed by short consensus repeat (SCR) domains that contain 6 conserved cysteine residues. E-Selectin participates in the interaction between leukocytes and the endothelium and appears to be involved in the pathogenesis of atherosclerosis.

Integrin beta 1, also known as CD29, is a 130 kDa transmembrane glycoprotein that forms noncovalent complexes with various Integrin alpha subunits (including alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, and alpha 6, also known as CD49a, CD49b, CD49c, CD49d, CD49e, and CD49f, respectively) to form the functional receptors that bind to specific extracellular matrix proteins. Integrin receptors are involved in the regulation of a variety of important biological functions, including embryonic development, wound repair, hemostasis, and prevention of programmed cell death. They are also implicated in abnormal pathological states such as tumor directed angiogenesis, tumor cell growth, and metastasis. These heterodimeric receptors bridge the cytoplasmic actin cytoskeleton with proteins present in the extracellular matrix and/or on adjacent cells. The clustering of integrins on a cell surface leads to the formation of focal contacts. Interactions between integrins and the extracellular matrix l

CD-2 interacts with lymphocyte function-associated antigen (lfa-3) and cd48/bcm1 to mediate adhesion between t-cells and other cell types. CD2 is implicated in the triggering of t- cells, the cytoplasmic domain is implicated in the signaling function.