CD19CD20

CD19 and CD20 are surface antigens expressed on B lymphocytes and are frequently discussed together in immunology and clinical practice. CD19 is widely expressed from early B cell development through most mature B cells and is often absent on plasmablasts and plasma cells; CD20 appears on mature B cells from the pre-B stage onward and is generally not present on stem cells or plasma cells. Together, CD19 and CD20 are used to identify B cell populations in immunophenotyping by flow cytometry.

CD19 functions as a signaling co-receptor that lowers the threshold for B cell receptor (BCR) signaling and amplifies B cell activation; it forms a signaling complex with other molecules such as CD21 and CD79. CD20's precise biological function is less clearly defined, but it is involved in regulation of B cell activation and calcium signaling; it is believed to play a role in B cell cycle progression and differentiation.

Clinically, CD19 and CD20 are important targets. Anti-CD20 monoclonal antibodies (for example rituximab, obinutuzumab, ofatumumab) are used to treat various B cell malignancies and some autoimmune diseases. Anti-CD19 strategies include CAR-T cell therapies (for example tisagenlecleucel, axicabtagene ciloleucel) for certain B cell cancers. Resistance can arise through downregulation or loss of antigen expression, including CD19-negative relapses after CAR-T therapy or CD20-negative relapses after anti-CD20 therapy.

In diagnostics, CD19 and CD20 are standard markers used to identify B cells and distinguish them from other lineages in flow cytometry and immunohistochemistry.