Expression of bone specific alkaline phosphatase on human B cells

We here report for the first time that human B cell express bone specific alkaline phosphatase. Using a monoclonal antibody against bone specific alkaline phosphatase (BAP), its expression was detected in approximately 50% of circulating B cells but not T cells. Using RT-PCR, BAP specific transcripts were detected in the B cells expressing surface BAP but not in those not expressing BAP. Activation of B lymphocytes using phorbal ester, PMA with or without ionomycin did not affect change in BAP expression. Following stimulations with Pokeweed Mitogen (PWM) and Staphylococcus aureus Cowan I (SAC), BAP expression on human B cells was increased. This paralleled the increase in production of immunoglobulins and BAP, detected by ELISA and enzyme assay with p-nitrophenyl phosphate, respectively. The role of BAP in B cell biology is uncertain. However, these data suggest that BAP may play an important role in differentiation and maturation of human B cells.