CD21

Also called CR2, C3d receptor, EBV receptor

Binds to Epstein Barr virus (EBV) and HHV8 (J Virol 2005;79:4651), breakdown products of complement component C3 (C3d), CD23 (plays a role in IgE synthesis) and possibly gamma interferon

Follicular dendritic cells produce a different isoform of CD21 than B cells (J Exp Med 1997;185:165)

CD21, CD23 and CD35 are dendritic cell markers

Hodgkin’s lymphoma demonstrates disruption of follicular dendritic cell-germinal cell clusters (evaluated by CD21 and CD23)

Note: although CD21 is the receptor for EBV, it is not necessarily expressed in EBV+ tumors

Shows variability in flow cytometry expression between specimens from same patient (AJCP 2002;117:615)

Uses: diagnose follicular dendritic cell sarcomas (AJSP 1996;20:944); assess follicular dendritic cell meshwork infrastructure (AJCP 2005;124:182, AJSP 2001;25:388), distinguish cutaneous or nodal mantle cell lymphoma from follicular lymphoma (AJSP 2001;25:732, Int J Surg Pathol 2005;13:73), distinguish splenic littoral cell angioma (CD21+ lining cells) from splenic hamartomas (CD21-, AJSP 1997;21:827), confirm that atypical cells have follicular dendritic origin in fine needle aspirates of hyaline-vascular Castleman’s disease (Diagn Cytopathol 2000;22:230)

Micro images: normal germinal center

follicular dendritic cell sarcoma - (1) liver (figure 2B); (2) figure 1: liver tumor (inset: splenic tumor); 2a/b: H&E; 2c: CD21; 2d: CD35; (3) stomach (figure 4 is CD21/CD35 cocktail)

follicular lymphoma - well organized clusters of dendritic cells in follicular lymphoma #1 (testicular)); #2 (head and neck); #3 (head and neck); peripheral T cell lymphoma resembling follicular lymphoma

Positive staining (normal): mature B cells (particularly marginal and mantle cells), follicular dendritic cells, pharyngeal and cervical epithelial cells, some thymocytes, some T cells

Positive staining (tumors): follicular dendritic cell sarcoma (AJSP 2004;28:988, AJSP 2001;25:721), hairy cell leukemia, B cell lymphomas (particularly mantle and marginal zone), hyaline vascular variant of Castleman's disease (AJSP 2002;26:662), splenic littoral cell angiomas (lining cells are CD21+, AJSP 1997;21:827), some T-ALL

Negative staining: dendritic cell neurofibroma with pseudorosettes (AJSP 2001;25:587), interdigitating dendritic cell sarcoma (AJCP 2001;115:589), histiocytic sarcoma (AJSP 2004;28:1133), inflammatory fibroid polyps of GI tract (AJSP 2004;28:107), splenic hamartomas, plasma cells

References: AJSP 2001;25:721, Mod Path 2002;15:50, OMIM 120650