CD21 antibody

Background of CD21 antibody

The CD21 antigen is expressed on mature B cells, follicular dendritic cells and pharyngeal and cervical epithelial cells [1,2]. CD21, also known as the Complement receptor type 2 (CR2) or Epstein-Barr virus (EBV) receptor, is a receptor for the C3 activation fragments iC3b and C3d. CD21 is part of a multimeric complex on B cells which includes CD19 and CD81 [3]. The ligand for CD21 is generated during activation of complement by the attachment of C3d to potential antigen. This creates fusion proteins that may cross-link the CD19-CD21-CD81 complex to sIg on antigen-specific B cells. The resulting signal transduction lowers the threshold for cellular activation. This enables an antibody reaction to natural protein antigens containing only one or a few epitopes and therefore unable to effectively cross-link Ig molecules on specific B cells. For example, keyhole limpet hemocyanin (KLH) immune complexes can be taken up and processed by all CR2-bearing B cells, regardless of their antigen specificity. KLH immune complexes taken up this way by non-specific B cells were shown to be presented to KLH-specific, MHC class II Th cells. CD23 may also serve as a ligand for CD21 [3].