Anti-CD21 antibodies are useful reagents for the immunodetection and measurement of CD21 in various samples. CD21 is a reported alias name for the human gene CR2, or 'complement C3d receptor 2'. The 1033-amino acid protein is a member of the Receptors of complement activation (RCA) family. The cellular localization is predicted to be membrane-associated. Glycosylation sites have been reported.