Human CD21 Antibody

CD21 (also called EBV receptor or CR2) is a 145 kDa member of the RCA (receptors of complement activation) family of proteins. It is expressed on T cells, B cells, and follicular dendritic cells. On the B cell surface, it combines with the BCR and CD19 to form a B cell activating complex. Mature human CD21 is 1013 amino acids (aa) in length. It is a type I transmembrane (TM) protein that contains a 951 aa extracellular domain (ECD) (aa 21-971) and a short 34 aa cytoplasmic tail. The ECD exhibits fifteen 60 aa SUSHI repeats. Soluble CD21 can be generated by cleavage near the TM domain. One potential splice variant shows a deletion of aa 847‑908, while another shows an insertion of 59 aa after Lys659. The ECD of human CD21 shares 71% aa identity with mouse CD21 ECD.