HB5 recognizes CD21, a type I membrane glycoprotein. Expression of CD21 in humans is found on B cells, follicular dendritic cells, subsets of epithelial cells, and thymic T cells. The primary function attributed to CD21 has been to amplify the B cell receptor (BCR)-mediated signal transduction in response to antigen recognition. To enhance the BCR mediated activation, CD21 associates with CD19 and CD81 in a B cell–specific signal transduction complex, where interaction of BCR with CR2/CD19 amplifies the signals. In addition, CD21 serves as a receptor for split products of complement protein C3, the gp350/220 viral coat protein of the EBV and the immunoregulatory protein CD23.
Applications
Reagent can be used for immunophenotyping by flow cytometry. Abnormal numbers of cells expressing this antigen or aberrant expression levels of the antigen can be expected in some disease states. It is important to understand the normal expression pattern for this antigen and its relationship to expression of other relevant antigens in order to perform appropriate analysis.
Expression of CD21 may be used as aid to diagnostic in the characterization of samples from individuals suspected with hematologic neoplasia.
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