CD20 is a human B-lymphocyte surface molecule that spans the membrane four times and is expressed on both normal and malignant cells. The CD20 antigen displays a unique expression pattern among hematopoietic cells - it is present on human pre B-lymphocytes and B-lymphocytes at all stages of maturation (except for plasma cells). Low CD20 antigen expression levels have been detected on normal T-lymphocytes. It functions as a B-cell activation receptor and B-lymphocyte development and differentiation agent, presumably through modulating intracellular calcium levels.
