Complement receptor type 2 (CR2), also known as complement C3d receptor, Epstein–Barr virus receptor, and CD21 (cluster of differentiation 21), is a protein that in humans is encoded by the CR2 gene. CR2 is involved in the complement system. It binds to iC3b (inactive derivative of C3b), C3dg, or C3d. [5]

Binding of C3b to a target surface is associated with exposure of epitopes in C3 that act as ligands for complement receptors 1–4 (CR1–4). Two of these receptors, CR1 (CD35) and CR2 (CD21), are short consensus repeats (SCR) consisting of 30 (10,11) and 15 or 16 (due to alternative splicing) (12,13) residues, respectively.

Complement receptors recognize either the C3 proteolytically activated fragments C3b, iC3b, and C3dg deposited on opsonized surfaces (CR1 to CR4 and CRIg) or the soluble anaphylatoxins released during alternative pathway activation (C3aR) or terminal pathway activation (C5aR1/C5aR2).

CD21 contains an extracellular domain of 15 or 16 repeating structural elements called short consensus repeats (SCRs), a membrane-spanning region, and a 34 amino acid cytoplasmic domain (Moore et al. 1987; Weis et al. 1986). hCD21 …

Apr 4, 2017 · Whereas binding of iC3b to CR2 (CD21) on B- and follicular dendritic cells elicits adaptive immune responses (5), interaction with integrin receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) enables phagocytosis of opsonized particles (6).

Aug 18, 2023 · Forms a complex with CD19, CD81 and CD225 in the membrane of mature B cells; complex is often called the B cell coreceptor complex, because CD21 binds to antigens through attached C3d (or iC3b or C3dg) when the membrane IgM binds to the antigen, which results in a greatly enhanced response B cell response to the antigen

Previous studies have shown that an optimal humoral response to a primary protein antigen requires C3 and CR2 (CD21). Sera from non-immunized donors contain natural IgM and IgG antibodies to the primary antigen keyhole limpet haemocyanin (KLH), and ...

Jun 28, 2015 · CD21 binds complement fragments C3d, C3dg and iC3b that are covalently bound to target antigens 27, 28. In addition, CD21 has been proposed to bind ligands such as the Epstein–Barr virus (EBV) envelope glycoprotein gp350/220 29, the low affinity Fc-receptor for IgE (FcεRII or CD23) 30, the cytokine interferon-alpha (IFN-α) 31.

Human complement receptor type 2 (CR2; CD21) is a surface-associated glycoprotein which binds to a variety of endogenous ligands, including the complement component C3 fragments iC3b, C3dg and C3d, the low-affinity IgE receptor CD23, and the type I cytokine, interferon-alpha.

Aug 1, 2001 · We measured the kinetics of binding of the receptor to its ligands, examined the influence of ionic contacts on these interactions, and assessed whether immobilized and soluble iC3b bound with similar kinetics to CR2.