Recombinant Human CD21 Protein, CF
Recombinant Human CD21 Protein, CF Summary
Ile21-Arg971, with a C-terminal 6-His tag
CF stands for Carrier Free (CF). We typically add Bovine Serum Albumin (BSA) as a carrier protein to our recombinant proteins. Adding a carrier protein enhances protein stability, increases shelf-life, and allows the recombinant protein to be stored at a more dilute concentration. The carrier free version does not contain BSA.
In general, we advise purchasing the recombinant protein with BSA for use in cell or tissue culture, or as an ELISA standard. In contrast, the carrier free protein is recommended for applications, in which the presence of BSA could interfere.
|Formulation||Lyophilized from a 0.2 μm filtered solution in PBS.|
|Reconstitution||Reconstitute at 500 μg/mL in PBS.|
|Shipping||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.
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).
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