CD21, or Complement component (3d/Epstein Barr virus) receptor 2, is a human gene encoded by CR2. It may also be known as: Complement receptor type 2; Cr2; Complement C3d receptor; Epstein-Barr virus receptor; EBV receptor; CD antigen CD21; C3DR; CVID7; SLEB9. The encoded protein has an amino acid length of 1033 and a mass of 112.9 kDa. CD21 is a member of the Receptors of complement activation (RCA) family. Homologs of this gene exist in other organisms, including: Mouse, Rat.