Human CD21 Biotinylated Antibody

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Human CD21 Biotinylated Antibody Summary

Species Reactivity
Detects human CD21 in Western blots.
Polyclonal Sheep IgG
Antigen Affinity-purified
Chinese hamster ovary cell line CHO-derived recombinant human CD21
Accession # P20023
Lyophilized from a 0.2 μm filtered solution in PBS with BSA as a carrier protein.


Recommended Concentration
Western Blot
0.1 µg/mL
Recombinant Human CD21 (Catalog # 4909-CD)

Please Note: Optimal dilutions should be determined by each laboratory for each application. General Protocols are available in the Technical Information section on our website.

Reconstitution Calculator

Reconstitution Calculator

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Preparation and Storage

Reconstitute at 0.2 mg/mL in sterile PBS.
Reconstitution Buffer Available
Reconstitution Buffer 1 (PBS)
Catalog #
Size / Price
The product is shipped at ambient temperature. Upon receipt, store it immediately at the temperature recommended below.
Stability & Storage
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.
  • 6 months, -20 to -70 °C under sterile conditions after reconstitution.

Background: CD21

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.
Entrez Gene IDs
1380 (Human); 12902 (Mouse); 289395 (Rat)
Alternate Names
C3DR; C3DRSLEB9; 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

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