rituximab

By Jennifer Jones, M.S.

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.

CD16 is a lymphocyte Fc gamma type III low-affinity receptor for IgG and is represented by two similar genes, CD16A (Fc gamma RIII A) and CD16B (Fc gamma RIIIB). CD16A exists as a heterooligomeric polypeptide-anchored form in macrophages and NK cells. CD16B exists as a monomeric glycosylphosphatidylinositol (GPI)-anchored form in neutrophils. CD16 binds IgG in the form of immune complexes or free antibody. It exhibits preferential binding to IgG1 and IgG3 isotypes, with minimal binding of IgG2 and IgG4.