Antigen distribution: 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 antibodies have been shown to bind CD23 and IFN-a. CD21 is part of a multimeric complex on B cells which includes CD19 and CD81 [3]. B-ly4 was clustered at the Leucocyte Typing Workshop IV [5].Cellular Expression: Mature B cells, follicular dendritic cells