CD20

CD20 is a membrane-bound protein on the surface of B lymphocytes, commonly referred to as B lymphocyte antigen CD20. It is encoded by the MS4A1 gene and is used as a widely recognized marker to identify mature B cells in research and clinical diagnostics. CD20 is expressed from the pre-B cell stage onward to memory B cells, but it is absent on pro-B cells, plasma cells, and most non-B cell lineages.

Structurally, CD20 is a four-pass transmembrane protein with both its N- and C-termini located inside the cell. It has two extracellular loops that are accessible to circulating antibodies. The protein is a relatively small surface antigen and is not essential for B cell development, but it participates in the regulation of B cell activation and calcium signaling, contributing to the maintenance and function of mature B cells. The precise physiological role of CD20 remains an area of ongoing research.

Clinically, CD20 is a major therapeutic target in B cell–related diseases. Monoclonal antibodies directed against CD20, such as rituximab, obinutuzumab, and ofatumumab, are used to treat various B cell malignancies including non-Hodgkin lymphoma and chronic lymphocytic leukemia, as well as some autoimmune disorders. These therapies deplete CD20-expressing B cells through mechanisms including antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, as well as direct effects on B cell signaling. CD20 expression is routinely assessed by flow cytometry to diagnose and monitor B cell–related conditions.

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