CD21


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CD21

a type I transmembrane protein found on B cells, follicular dendritic cells, pharyngeal and cervical epithelial cells, some thymocytes, and some T cells that plays a role in signal transduction; expressed in hairy cell leukemia, B-cell lymphoma, and some T-cell acute lymphocytic leukemias.
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They are identified immunohistochemically by their reactivity for CD21 (C3d receptor), CD35 (C3b receptor), Ki-M4p, and Ki-FDRC1p antibodies.
CD21 reveals that the follicular dendritic mesh work is located in the peripheral part of the follicles (original magnification X20).
(3,8,9,17,24) This process can occur via an FDC lineage expressing CD21, CD23, and CD35, or rarely via a myofibroblastic (or FBRC) lineage expressing vimentin and SMA.
CD21 immunohistochemical stain highlighting follicular dendritic cell sarcoma spindle cells (original magnification X20).
CD21 highlights expanded follicular dendritic cell meshworks that show disruption in the later stages of progression (Figure 5, F).
(15) Normal smooth muscle cells have been shown to express the CD21 receptor (15) or a protein with a related, cross-reactive epitope.
(27) Unlike FDCS, interdigitating dendritic cell sarcomas are diffusely positive for S100, negative for dendritic cell markers (CD21, CD35), and lack desmosomes on electron microscopy.
If NLPHL is in the differential diagnosis, a marker of follicular dendritic cells such as CD21 to evaluate for nodules, or a marker of follicular T cells such as PD1 to evaluate for rosettes around the large cells, may be helpful.
Follicular dendritic cell sarcoma usually occurs at nodal sites and is positive for CD21 (which is only occasionally and focally expressed in AFH) and CD35 but lacks both desmin and smooth muscle actin.
CD21 stain is useful in highlighting the follicular dendritic cells of lymphoid follicles present in the lesion.
Immunophenotypically, neoplastic cells express CD20, CD79a, CD21 and CD35.
A series of complex reactions between B-cell receptors (such as TACI, BAFFR, and BCMA) and B-cell-maturation regulatory molecules (such as B-cell-activating factor [BAFF] and a proliferationinducing ligand [APRIL]) is important in the development and maintenance of B cells and consequently humoral immunity (Figure 1).7 Other identified mutations include autosomal-recessive mutations in BAFFR, CD20, CD19, CD81, CD21, and inducible T-cell costimulator (ICOS).