Recombinant Human CD21 Protein, CF


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Product Details

Reactivity HuSpecies Glossary
Applications Binding Activity

Order Details

Recombinant Human CD21 Protein, CF Summary

Details of Functionality
Measured by its binding ability in a functional ELISA. When CD21 is coated at 5 μg/mL, complement component iC3b binds with apparent KD <10 nM.
Chinese Hamster Ovary cell line, CHO-derived human CD21 protein
Ile21-Arg971, with a C-terminal 6-His tag
Accession #
N-terminal Sequence
Protein/Peptide Type
Recombinant Proteins
>95%, by SDS-PAGE under reducing conditions and visualized by silver stain
Endotoxin Note
<0.01 EU per 1 μg of the protein by the LAL method.


Theoretical MW
105 kDa.
Disclaimer note: The observed molecular weight of the protein may vary from the listed predicted molecular weight due to post translational modifications, post translation cleavages, relative charges, and other experimental factors.
130-140 kDa, reducing conditions

Packaging, Storage & Formulations

Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
  • 12 months from date of receipt, -20 to -70 °C as supplied.
  • 1 month, 2 to 8 °C under sterile conditions after reconstitution.
  • 3 months, -20 to -70 °C under sterile conditions after reconstitution.
Lyophilized from a 0.2 μm filtered solution in PBS.
>95%, by SDS-PAGE under reducing conditions and visualized by silver stain
Reconstitution Instructions
Reconstitute at 500 μg/mL in PBS.


This product is produced by and ships from R&D Systems, Inc., a Bio-Techne brand.

Alternate Names for Recombinant Human CD21 Protein, CF

  • C3DR
  • CD21 antigen
  • CD21
  • Complement C3d receptor
  • complement component (3d/Epstein Barr virus) receptor 2
  • complement receptor type 2
  • CR2
  • EBV receptor
  • Epstein-Barr virus receptor


CD21, also known as complement receptor 2 (CR2), is a 145 kDa N-glycosylated member of the RCA (regulators of complement activation) family of proteins. The complement cascade plays an important role in the innate immune system through the recognition and clearance of immune complexes and foreign particles (1). Mature human CD21 contains a 951 aa extracellular domain (ECD) with fifteen tandem SCR/SUSHI repeats, a 28 aa transmembrane segment, and a 34 aa cytoplasmic tail (2, 3). Within the ECD human CD21 shares 67% aa identity with mouse and rat CD21. Human CD21 and CD35 are encoded by two separate genes, but in mouse partially homologous proteins are alternate splice forms of one gene (4). Alternate splicing of human CD21 generates isoforms with an altered SCR8 or an insertion between SCR10 and SCR11 (5). CD21 is primarily expressed on B cells, follicular dendritic cells, and T cells. A circulating soluble form of CD21 is released by proteolytic shedding from activated B cells (6, 7). CD21 binds the complement component fragments iC3b, C3d, and C3d,g (1, 8). It forms a complex with the B cell receptor-associated CD19 molecule and lowers the threshold for B cell activation (9 - 11). CD21 can also form complexes with the complement receptor CD35/CR1 (1, 10). Mice deficient in both CD21 and CD35 exhibit normal B cell development but severely compromised germinal center development, antibody production, establishment of protective microbial immunity, and B cell tolerance to self antigens (12, 13). In mice, CD21/CD35 must additionally be present on follicular dendritic cells to mount effective humoral responses and establishment of B cell memory (14). CD21 also binds the gp350 coat protein on Epstein-Barr virus and serves as an uptake receptor for viral infection of B cells (15).
  1. Roozendaal, R. and M.C. Carroll (2007) Immunol. Rev. 219:157.
  2. Weis, J.J. et al. (1988) J. Exp. Med. 167:1047.
  3. Moore, M.D. et al. (1987) Proc. Natl. Acad. Sci. 84:9194.
  4. Kurtz, C.B. et al. (1990) J. Immunol. 144:3581.
  5. Barel, M. et al. (1998) Mol. Immunol. 35:1025.
  6. Masilamani, M. et al. (2003) Eur. J. Immunol. 33:2391.
  7. Sengstake, S. et al. (2006) Int. Immunol. 18:1171.
  8. Carel, J.-C. et al. (1990) J. Biol. Chem. 265:12293.
  9. Matsumoto, A.K. et al. (1991) J. Exp. Med. 173:55.
  10. Tuveson, D.A. et al. (1991) J. Exp. Med. 173:1083.
  11. Dempsey, P.W. et al. (1996) Science 271:348.
  12. Haas, K.M. et al. (2002) Immunity 17:713.
  13. Prodeus, A.P. et al. (1998) Immunity 9:721.
  14. Rossbacher, J. et al. (2006) Eur. J. Immunol. 36:2384.
  15. Tanner, J. et al. (1987) Cell 50:203.

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Gene Symbol CR2