CR2 Gene - Complement C3d Receptor 2 (CD21) | Function, Mutations & Disease

The CR2 gene encodes complement receptor type 2 (CD21), a membrane protein expressed on mature B cells, follicular dendritic cells, and some T cells. It binds complement fragments iC3b, C3dg, and C3d, and serves as the receptor for Epstein-Barr virus (EBV). CR2 forms a complex with CD19 and CD81 to modulate B cell activation and immune response. Mutations in CR2 are associated with immunodeficiency and systemic lupus erythematosus.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• Complement cascade (Reactome: R-HSA-166658)

• B cell receptor signaling (Reactome: R-HSA-983705)

• Epstein-Barr virus infection (KEGG: hsa05169)

CR2 (CD21) is a 145 kDa type I transmembrane glycoprotein composed of 15-16 short consensus repeats (SCRs) in its extracellular domain. It binds complement fragments iC3b, C3dg, and C3d, and serves as the receptor for Epstein-Barr virus (EBV). CR2 forms a signaling complex with CD19 and CD81 on B cells, lowering the threshold for B cell activation. It is also expressed on follicular dendritic cells, where it retains immune complexes to facilitate antigen presentation. Mutations in CR2 cause common variable immunodeficiency type 7 (CVID7) and increase susceptibility to systemic lupus erythematosus.