Phospholipid metabolism and T cell activation: receptor triggering is associated with the inhibition of phosphatidylserine synthesis.

Activation of Jurkat T lymphocytes to produce IL2 is accompanied by a strong inhibition of phosphatidylserine (PS) synthesis. This inhibition was obtained either with the mitogenic lectin PHA, anti-CD3 monoclonal antibodies (mAb), anti-CD2 mAb or anti-Ti mAb. Bypassing membrane receptor signalling, by using a Ca2+ ionophore or a protein phosphatase inhibitor, sodium ortho-vanadate, also results in a marked inhibition of PS synthesis. Activators of phospholipid -Ca2+ dependent protein kinase C (PKC) did not significantly modify PS synthesis, suggesting that the observed changes only involve the transduction of the first activation signal. PS being a necessary cofactor for PKC, our results strongly suggest that the inhibition of PS synthesis induced by receptor triggering exerts a feed back control on PKC therefore leading to a transient activation of the enzyme upon full lymphocyte activation.