Expression of bone specific alkaline phosphatase on human B cells (86.18)

Abstract

Abstract A complex relationship exists among the molecules involved in the development of the immune system and of the bony skeleton. Molecules involved in one system can exert effects on the other system. Alkaline phosphatase (AP) is produced at high levels by osteoblasts and it plays an important role in bone remodeling. AP activity is also found on human B cells although the exact nature is not clearly understood. The purpose of this study is to determine the nature of expression of AP in human lymphocytes. 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. These cells were distinct from the circulating osteoblasts. Lymphocyte stimulation by TPA with or without ionomycin, did not change BAP expression. Using RT-PCR, BAP specific transcripts were detected in the B cells expressing surface BAP but not in those not expressing BAP. The expression of BAP on B cells was similar in children as in adults. Its expression on transformed B cell lines was variable and EBV-transformed B cells did not express BAP. BAP was predominantly expressed in the CD27negative subpopulation. As CD27 is thought to be a marker for memory lymphocytes, it might be inferred that BAP is down-regulated in the memory B cells. Collectively, these data suggest that BAP may play an important role in the differentiation and maturation of human B cells.