Complement receptor type 2 (CD21) (CD21)

Complement receptor type 2 (CD21) is a 145-kDa type I transmembrane glycoprotein primarily expressed on mature B cells and follicular dendritic cells [1.1.1, 1.1.4]. It serves as a critical component of the B-cell co-receptor complex, alongside CD19 and CD81, where it binds to C3d-opsonized antigens to significantly lower the threshold for B-cell activation [1.1.1, 1.1.4]. Beyond its role in the complement system, CD21 is the primary receptor for the Epstein-Barr virus (EBV), facilitating viral entry into B cells and certain T-cell subsets [1.1.2, 1.2.4]. In pathology, CD21 is involved in the pathogenesis of autoimmune diseases like systemic lupus erythematosus and is aberrantly expressed in various malignancies, including B-cell lymphomas and T-cell acute lymphoblastic leukemia (T-ALL) [1.1.2, 1.3.2]. Therapeutic strategies targeting CD21 include the development of chimeric antigen receptor (CAR) T-cell therapies for T-ALL and monoclonal antibodies aimed at modulating humoral immunity or blocking viral infection [1.3.1, 1.3.2]. Additionally, CD21 expression levels can influence the efficacy of other B-cell targeted therapies, such as anti-CD19 antibody-drug conjugates [1.2.1, 1.5.1].

Other names

CR2C3DREBV receptorComplement C3d receptorCluster of differentiation 21Epstein-Barr virus receptor

CD21-targeted therapies work by either inducing direct cell death in CD21-positive malignant cells via chimeric antigen receptor (CAR) T-cell activity or by neutralizing the receptor with monoclonal antibodies to inhibit B-cell co-stimulation and block the entry of the Epstein-Barr virus.