Role of a serum phospholipase A₁in the phosphatidylserine‐induced T cell inhibition

Abstract

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.

Lysophosphatidylserine has Bilateral Effects on Macrophages in the Pathogenesis of Atherosclerosis

“…After 24 hours, the total RNA of the cells was purified using the GenElute mammalian total RNA Miniprep kit (Sigma-Aldrich Co.) and LysoPS is thought to act as a potent lipid mediator, similar to LysoPA and S1P 9) . For example, LysoPS stimulates the degranulation of mast cells 10,11) , suppresses the proliferation of T lymphocytes 12) and induces apoptotic cell engulfment by macrophages 13,14) .…”

A Novel Phosphatidic Acid-selective Phospholipase A1That Produces Lysophosphatidic Acid

“…We have purified and cloned a cDNA for phosphatidylserine-specific PLA 1 (PS-PLA 1 ), a member of the lipase family, from the culture medium of activated rat platelets. PS-PLA 1 specifically hydrolyzes PS (24) and produces 2-acyl-lysophosphatidylserine (LPS), which is a lipid mediator for mast cells (25), T cells (26), and neural cells (27). We recently showed that PS-PLA 1 stimulates histamine release from rat peritoneal mast cells by hydrolyzing PS exposed on the surface of some cell types such as apoptotic cells and activated platelets (25).…”

An Alternative Splicing Form of Phosphatidylserine-specific Phospholipase A1 That Exhibits Lysophosphatidylserine-specific Lysophospholipase Activity in Humans

“…For example, lyso-PS is demonstrated to interact with local mast cells (17), producing specific and stereoselective activation (18). It also induces transient increases in cytosolic free Ca 2ϩ ([Ca 2ϩ ] i ) in ovarian and breast cancer cells (19) and lyso-PS; 2-acyl-1-lyso-PS with unsaturated fatty acids especially inhibits mitogen-induced T cell activation (20). Lyso-PS is present in human serum, the aqueous humor and the lachrymal gland fluid of the eye (21).…”