Expression of CD9 (p24) antigen on hematopoietic cells following treatment with phorbol ester

Expression of the leukemia-associated cell surface antigen p24 (CD9) on human hematopoietic cell lines and B-cell chronic lymphocytic leukemia (B-CLL) cells was analyzed before and after treatment with the phorbol ester 12-o-tetradecanoyl-phorbol 13-acetate (TPA). Little or no expression of CD9 was detected in any of the cell lines used or in B-CLLs before treatment with TPA. After exposure to TPA, HL-60, Epstein-Barr virus-immortalized B-cell lines, Molt-3, MT-2 and B-CLLs showed markedly augmented CD9 expression. U937 and K562 showed slight increases of CD9 expression. However, no expression of CD9 was induced in CCRF-CEM or HUT-102. Although CD9 is known to be one of the most useful markers of pre-B-cell common acute lymphoblastic leukemia, the expression of CD9 does not seem to be restricted to any specific cell lineage and can be induced in various hematopoietic cell lineages by treatment with TPA.