Anti-CD21 Monoclonal Antibody

CD21 is a 145 kD transmembrane protein also known as complement C3d receptor (C3dR), complement receptor 2 (CR2), and Epstein-Barr virus receptor. CD21 is expressed on B cells, follicular dendritic cells, subsets of normal thymocytes and T cells, and some epithelial cells. CD21 is the receptor used by Epstein-Barr virus to infect B cells and is also the complement receptor for C3d. CD21 has also been shown to interact with a number of proteins, including CD23, CD19, annexin VI, CD81, iC3b, complement receptor 1 (CR1, CD35), and interferon-alpha 1 (IFN-alpha1). Protein function: Serves as a receptor for various ligands including complement component CD3d, HNRNPU OR IFNA1 (PubMed:1849076, PubMed:21527715, PubMed:7753047). When C3d is bound to antigens, attaches to C3d on B- cell surface and thereby facilitates the recognition and uptake of antigens by B-cells (PubMed:21527715). This interaction enhances B-cell activation and subsequent immune responses. Forms a complex with several partners on the surface of B-cells including CD19, FCRL5 and CD81, to form the B-cell coreceptor complex that plays a crucial role in B-cell activation and signaling (PubMed:1383329, PubMed:30107486). Also induces specific intracellular signaling separately from the BCR and CD19 by activating the tyrosine kinase SRC, which then phosphorylates nucleolin/NCL and triggers AKT and GSK3 kinase activities in a SYK/CD19-independent manner (PubMed:12938232). Acts as a ligand for CD23 (FcepsilonRII), a low-affinity receptor for IgE, which is expressed on B-cells and other immune cells, and thus participates in the regulation of IgE production (PubMed:1386409). [The UniProt Consortium]