CD21

CD21 is a single chain transmembrane glycoprotein that has various functions such as promoting B cell proliferation, forming immune memory, and activating complement system. As a specific molecular marker of follicular dendritic cells (FDCs), CD21 can be used for diagnosing follicular lymphoma (FL) and angioimmunoblastic T cell lymphoma (AITCL), which is because FDCs grow expansively in the follicles of FL, but surround high endothelial vessels outside the follicles of AITCL. Meanwhile, CD21 is an important diagnostic biomarker for FDC sarcoma (FDCS). For example, it is highly expressed in nasopharyngeal FDCS but down-regulated or even absent in nasopharyngeal carcinoma, which makes it useful for assisting in identification. Moreover, CD21 is an EB virus (EBV) receptor, and it can mediate EBV to infect cells and induce malignant transformation. Therefore, CD21 can assist in the diagnosis of EBV related diseases such as Burkitt lymphoma, nodular sclerosis Hodgkin lymphoma, inflammatory FDCS, etc. In addition, CD21 positivity is considered as a good prognostic indicator for patients with diffuse large B cell lymphoma.