Background：CD21 is also called the complement receptor 2 type （CR2） and EB virus receptor, is a member of the complement activation regulators family.CD21 is mainly distributed in mature B cells, dendritic cells in lymphoid follicles, and part of the T cells. The functions of CD21 include promoting proliferation of B cell, mediating transformation of EBV to B cells and participating in immune memory. It is mainly used for diagnosis of follicular cell tumors and study of regulation of immune complement activation.
