Role of a serum phospholipase A1 in the phosphatidylserine-induced T cell inhibition.

We have previously shown that unsaturated phosphatidylserines inhibit mitogen-induced T cell activation. We now report that the inhibitory action requires a protein present in bovine and human serum. Partial purification and phospholipase assay show that this protein has phospholipase A activity on phosphatidylserine but not phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositol. In short incubations (1-3 h)2-acyl lysophosphatidylserine is produced but in longer incubations the cis-unsaturated fatty acid is also released. Experiments on peripheral blood mononuclear cells indicate that the unsaturated fatty acid becomes the main responsible for the PS-induced inhibition and that 2-acyl lysophosphatidylserine enhances the inhibitory effect of fatty acid.