CD53 is a member of the transmembrane 4 superfamily, also called the tetraspanin family. Most of these members are cell-surface proteins that are characterized by the presence of four hydrophobic domains. These proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. CD53 is a cell surface glycoprotein that is known to complex with integrins. Familial deficiency of CD53 gene has been linked to an immunodeficiency associated with recurrent infectious diseases caused by bacteria, fungi and viruses. CD53 contributes to the transduction of CD2-generated signals in T cells and natural killer cells and has been suggested to play a role in growth regulation.
CD55, also well known as decay-accelerating factor (DAF), is a member of the RCA (regulators of complement activation) family characterized by four to 30 SCRs (short consensus repeats) in their plasma-exposed regions. It is a major regulator of the alternative and classical pathways of complement activation and is expressed on all serum-exposed cells. CD55 is physiologically acting as an inhibitor of the complement system, but is also broadly expressed in malignant tumours. DAF seems to exert different functions beyond its immunological role such as promotion of tumorigenesis, decrease of complement mediated tumor cell lysis, autocrine loops for cell rescue and evasion of apoptosis, neoangiogenesis, invasiveness, cell motility. It is commonly hijacked by invading pathogens, including many enteroviruses and uropathogenic Escherichia coli, to promote cellular attachment prior to infection. This 70-75 kDa glycoprotein CD55 containing four SCR modules is involved in the regulation of the complement cascade. It inhibits complement activation by suppressing the function of C3/C5 convertases, thereby limiting local generation or deposition of C3a/C5a and membrane attack complex (MAC or C5b-9) production. DAF has been identified as a ligand for an activation-associated, seven-transmembrane lymphocyte receptor, CD97, which is a receptor mediating attachment and infection of several viruses and bacteria. In addition, it has been shown that DAF regulates the interplay between complement and T cell immunity in vivo, and thus may be implicated in immune and tumor biology.
CD55 is a 60-70 kD glycosylphosphatidylinositol (GPI)-anchored single chain glycoprotein also known as decay-accelerating factor (DAF). It is expressed on hematopoietic cells including erythrocytes and many non-hematopoietic cells. CD55 accelerates the dissociation of the components of the C3-convertases (namely C2a from C4b in the C4bC2a complex, a C3-convertase of the classical pathway, and factor Bb from the C3bBb complex, a C3-convertase of the alternative pathway) to protect cells from inappropriate damage caused by autologous complement. CD55 has been reported to reduce the efficiency of NK cell lysis and induce signal transduction in T cells. CD55 has also been shown to interact with CD97 and bind to Coxsackie and Echovirus.
Ligand of the T-lymphocyte CD2 glycoprotein. This interaction is important in mediating thymocyte interactions with thymic epithelial cells, antigen-independent and -dependent interactions of T-lymphocytes with target cells and antigen-presenting cells and the T-lymphocyte rosetting with erythrocytes. In addition, the LFA-3/CD2 interaction may prime response by both the CD2+ and LFA-3+ cells.
CD59 is a widely expressed membrane regulatory protein, and its C-terminus is fixed on the cell surface via a GPI anchor. CD59 has different names due to its functions, such as homologous restriction factor-20, protectin and membrane inhibitor of reactive lysis (MIRL). The main physiological function of CD59 is to prevent the complement membrane attack complex (MAC) from lysing and destroying cells of the same species or its own, that is, homologous species restriction (HSR).
CD5 is a 67 kD protein, also known as Lyt-1, Ly-1, T1, Tp67, or Ly-12. It is a member of the scavenger receptor cysteine-rich protein superfamily (SRCR) and primarily expressed on thymocytes, T cells, and B-1 cells. Although mature α/β T cells express high levels of CD5, very few γ/δ T cells express this antigen. The interaction of CD5 with CD72, gp35-37, TCR, or BCR is involved in T and B cell activation.
CD5, also known as Leu-1, is a type I transmembrane protein belonging to the scavenger receptor cysteine-rich (SRCR) superfamily. It is expressed on thymocytes, T cells and the B1a subpopulation of B cells. CD5 binds the C-type lectin, CD72, and modulates signaling through the antigen receptors on T and B cells. CD5 has been shown to provide either positive or negative co-stimulatory signals depending on cell type to regulate immune responses.
This gene encodes a cell surface adhesion molecule that belongs to a family of adhesion/homing receptors. The encoded protein contains a C-type lectin-like domain, a calcium-binding epidermal growth factor-like domain, and two short complement-like repeats. The gene product is required for binding and subsequent rolling of leucocytes on endothelial cells, facilitating their migration into secondary lymphoid organs and inflammation sites. Single-nucleotide polymorphisms in this gene have been associated with various diseases including immunoglobulin A nephropathy. Alternatively spliced transcript variants have been found for this gene.
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