Role of Ecto-ATPase in Lymphocyte Function

Extracellular nucleotides are now recognized as mediators of immune and non-immune cell function. The effects of extracellular nucleotides also vary with tissue. For example, extracellular ATP in micromolar concentrations can form pores in cell membranes, resulting in osmotic changes that are detrimental to the cell1. In bone marrow and thymocytes, extracellular ATP stimulates DNA synthesis, but it inhibits DNA synthesis in spleen, lymph nodes and peripheral blood lymphocytes2. The nucleotide also has cytostatic and cytotoxic effects on some tumor cells3, but the mechanism is unknown. In addition, ATP triggers histamine secretion from mast cells4–6 and the secretion of granules from neutrophils and monocytes7, 8, but inhibits macrophage-9, 10, NK cell-11–13 mediated cytotoxicities. Furthermore, extracellular ATP may serve as a substrate for ectoprotein kinases14 which have been identified on neutrophils13, erythrocytes16, neuronal cells17 and fibroblasts18.