CD21 (complement receptor 2, CR2, C3D receptor, EBV receptor) binds C3 complement fragments, especially its breakdown fragments, which remain covalently attached to complement activating surfaces or antigen. CD21 has important roles in uptake and retention of immunocomplexes, survival of memory B cells and in development and maintenance of the humoral response to T-dependent antigens. CD21 also serves as a key receptor for Epstein-Barr virus binding and is involved in targeting prions to follicular dendritic cells and expediting neuroinvasion following peripheral exposure to prions. A soluble form of the CD21 (sCD21) is shed from the lymphocyte surface and retains its ability to bind respective ligands. CD21 functions as receptor for C3d, C3dg and iC3b complement components, for EBV and for IFNalpha. CD21 binds to CD23 and associates with CD19, CD81 and Leu13 to form a large signal-transduction complex involved in B cell activation. Genetic variations in the CD21 gene are associated with susceptibility to systemic lupus erythematosus type 9 (SLEB9). Alternatively, spliced transcript variants encoding different isoforms of CD21 have been found.
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Protein Aliases: C3-binding protein; C3b/C4b receptor; CD21; CD35; CD35 antigen; Complement C3d receptor; complement component (3b/4b) receptor 1 (Knops blood group); complement component (3d/Epstein Barr virus) receptor 2; complement component receptor 2; complement receptor 1 long isoform; Complement receptor type 1; Complement receptor type 2; Cr2; EBV receptor; Epstein-Barr virus receptor; Knops blood group antigen
Gene Aliases: BOS_15584; C3BR; C3DR; C4BR; CD21; CD35; CR; CR1; CR2; CVID7; KN; SLEB9