A phage antibody identifying an 80-kDa membrane glycoprotein exclusively expressed on a subpopulation of activated B cells and hairy cell leukemia B cells

We have isolated a phage display library-derived monoclonal antibody, phab V-3, that identifies a membrane glycoprotein of approximately 80 kDa which is expressed on a subpopulation of activated B lymphocytes in secondary lym phoid organs. In agreement with their activated phenotype, phab V-3(+) B ce lls display a blast-like morphology, and are prone to spontaneous apoptosis in vitro, unless rescued by stimulation with CD40 ligand (CD40L). The expr ession of the phab V-3 molecule coincides with B cells that produce high le vels of IgM, IgG and IgA in vitro upon stimulation with CD40L in combinatio n with IL-2 and IL-10. Immunofluorescent analysis of B cell malignancies un veiled that the phab V-3 molecule was uniquely expressed on hairy cell leuk emia (HCL) B cells. Similar to phab V-3(+) tonsils B cells, HCL B cells hav e been reported to express CD11c, CD95 and CD27, which might indicate that the phab V-3(+) B cells in HCL are the malignant counterpart of the phab V- 3(+) B cell subpopulation.