Activation and Up-regulation of Phospholipase D Expression by Lipopolysaccharide in Human Peripheral T Cells

In a previous study, we showed that bacterial LPS activates protein kinase C (PKC) and causes an intracellular pH (pHi) increase, but does not elevate intracellular calcium ([Ca2+]i) in human peripherial T cells. Hence this study aimed to investigate whether the activation of PKC was resulted from phospholipase D (PLD) catalysis by LPS. The activity of PLD was measured by the production of 3H-phosphatidylethanol from phosphatidic acid (PA), and the expression of PLD or IL-2 Ralpha was determined by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Enzyme-linked immunosorbent assay (ELISA) was used to analyze IL-2 and IL-4. Phytohemagglutinin (PHA), and phorbol 12-myristate 13-acetate (PMA) were used as controls. Our results indicated that (1) LPS-stimulated pHi elevation was PKC dependent; (2) After 30 min stimulation, LPS increased PLD activity via a measured production of 3H-phosphatidylethanol from phosphatidic acid and the initiation of PLD1a mRNA expression started; (2) LPS stimulated IL-2 R expression but not IL-2 and IL-4 secretion. Our findings suggested that the stimulation of PLD activity and its mRNA expression by LPS might be required for IL-2 R expression and a sustained PKC dependent pHi elevation but not for the secretion of IL-2 or IL-4 in human T cells. This indicated that LPS might enhance T cell adaptive immunity to resist Gram-negative bacterial infection.