CD21 Antibody | Complement Receptor 2 | CR2

	Catalog No	Formulation	Size	Price (USD)
	V3971-100UG	0.2 mg/ml in 1X PBS with 0.1 mg/ml BSA (US sourced) and 0.05% sodium azide	100 ug	539
Formulation
	V3971-20UG	0.2 mg/ml in 1X PBS with 0.1 mg/ml BSA (US sourced) and 0.05% sodium azide	20 ug	249
Formulation
	V3971SAF-100UG	1 mg/ml in 1X PBS; BSA free, sodium azide free	100 ug	539
Formulation
	V3971IHC-7ML	Prediluted in 1X PBS with 0.1 mg/ml BSA (US sourced) and 0.05% sodium azide; For IHC use only	7 ml	539
Formulation

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Western blot testing of human Raji cell lysate with CD21 antibody (clone CR2/2754). Although CD21 has a theoretical mass near 105 kDa, the mature receptor is extensively glycosylated and migrates at a higher apparent molecular weight which is consistent with published data (140-160 kDa).

Analysis of HuProt(TM) microarray containing more than 19,000 full-length human proteins using CD21 antibody (clone CR2/2754). These results demonstrate the foremost specificity of the CR2/2754 mAb.
Z- and S- score: The Z-score represents the strength of a signal that an antibody (in combination with a fluorescently-tagged anti-IgG secondary Ab) produces when binding to a particular protein on the HuProt(TM) array. Z-scores are described in units of standard deviations (SD's) above the mean value of all signals generated on that array. If the targets on the HuProt(TM) are arranged in descending order of the Z-score, the S-score is the difference (also in units of SD's) between the Z-scores. The S-score therefore represents the relative target specificity of an Ab to its intended target.

IHC testing of FFPE human tonsil tissue with CD21 antibody (clone CR2/2754). HIER: boil tissue sections in pH6, 10mM citrate buffer, for 10-20 min followed by cooling at RT for 20 min.

Immunofluorescent staining of PFA-fixed human MOLT4 cells with CD21 antibody (clone CR2/2754, green) and Reddot nuclear stain (red).

Flow cytometry staining of PFA-fixed human MOLT4 cells with CD21 antibody; Red=isotype control, Blue= CD21 antibody.

SDS-PAGE analysis of purified, BSA-free CD21 antibody (clone CR2/2754) as confirmation of integrity and purity.

IHC testing of FFPE human tonsil tissue with CD21 antibody (clone CR2/2754). Inset: PBS used in place of primary Ab (secondary Ab negative control). HIER: boil tissue sections in pH 9 10mM Tris with 1mM EDTA for 20 min and allow to cool before testing.

Availability	1-3 business days
Species Reactivity	Human
Format	Purified
Clonality	Monoclonal (mouse origin)
Isotype	Mouse IgG1, kappa
Clone Name	CR2/2754
Purity	Protein G affinity chromatography
UniProt	P20023
Localization	Cell surface
Applications	ELISA (order BSA/sodium Azide-free Format For Coating) : Flow Cytometry : 1-2ug/10^6 cells Western Blot : 1-2ug/ml Immunofluorescence : 1-2ug/ml Immunohistochemistry (FFPE) : 1-2ug/ml for 30 min at RT
Limitations	This CD21 antibody is available for research use only.
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Description

CD21 antibody detects CD21, also known as Complement Receptor 2 (CR2), a cell surface receptor involved in complement recognition, adaptive immunity, and B cell activation. The UniProt recommended name is Complement receptor type 2. CD21 is a type I transmembrane glycoprotein expressed primarily on mature B cells, follicular dendritic cells, subsets of T cells, and some epithelial populations. Through its ability to bind complement component C3d and related ligands, CD21 plays an essential role in lowering the activation threshold of B cells and enhancing antibody responses to foreign antigens.

Structurally, CD21 contains an extensive extracellular domain composed of multiple short consensus repeats characteristic of complement regulatory proteins. These domains mediate ligand binding and allow CD21 to interact with complement fragments, immune complexes, and viral proteins. CD21 associates with CD19 and CD81 to form the B cell coreceptor complex, a signaling module that amplifies B cell receptor responses. When C3d-tagged antigens engage this complex, B cells receive stronger activation signals, supporting proliferation, differentiation, germinal center formation, and the establishment of long-term humoral immunity.

The CD21 gene is located on chromosome 1q32 within the complement receptor cluster. Expression is highest in secondary lymphoid tissues including spleen, lymph nodes, and tonsils. In follicular dendritic cells, CD21 helps retain complement-opsonized antigens on the dendritic network, promoting efficient presentation to B cells during affinity maturation. In the thymus and peripheral tissues, CD21 expression on select T cell subsets may contribute to immune regulation, although these roles are not as fully defined as in B cells.

CD21 also serves as the cellular receptor for Epstein-Barr virus (EBV) on B cells. Viral binding to CD21 allows entry of EBV into the host cell, where it can establish latent or lytic infection depending on the context. This interaction contributes to EBV's tropism for B cells and underlies its involvement in several lymphoproliferative diseases. Studies of CD21 expression and regulation therefore extend into virology, immune tolerance, and cancer biology.

Altered CD21 levels are associated with several immune disorders. Reduced expression is seen in some autoimmune diseases, including systemic lupus erythematosus, where impaired complement receptor function may contribute to dysregulated immune complex handling. CD21 expression patterns also shift during B cell maturation, making it a useful marker for distinguishing naive, memory, and germinal center B cell subsets. In lymphomas, CD21 expression helps classify certain follicular dendritic cell tumors and B cell malignancies.

CD21 participates more broadly in complement regulation, immune complex trafficking, and the orchestration of B cell selection. Through its complement binding properties, CD21 contributes to clearance of apoptotic cells and modulation of inflammatory environments. Its presence on mucosal epithelial cells has prompted exploration into potential roles in barrier immunity and tissue-specific immune interactions.

Clone CR2/2754 is designed to recognize CD21 and is used by researchers to study B cell biology, complement receptor function, and immune cell subset characterization. It supports investigations into how complement-tagged antigens alter B cell activation thresholds, how follicular dendritic cells regulate antigen retention, and how CD21 expression changes in immune dysregulation or malignancy. As with all monoclonal reagents, clone CR2/2754 should be evaluated within each experimental system to determine appropriate conditions for detecting CR2 expression.

CD21 antibody (clone CR2/2754) is validated for use in relevant research applications to detect Complement Receptor 2 expression in cells and tissues. NSJ Bioreagents provides CD21 antibody reagents suitable for studies of B cell activation, complement biology, lymphoid tissue organization, and host-pathogen interactions.

Application Notes

Optimal dilution of the CD21 antibody should be determined by the researcher.

1. The prediluted format is supplied in a dropper bottle and is optimized for use in IHC. After epitope retrieval step (if required), drip mAb solution onto the tissue section and incubate at RT for 30 min.