IL-8-INDUCED SIGNAL-TRANSDUCTION IN T-LYMPHOCYTES INVOLVES RECEPTOR-MEDIATED ACTIVATION OF PHOSPHOLIPASE-C AND PHOSPHOLIPASE-D

We have characterized the IL-8-induced signal transduction processes i n T lymphocytes. A basal level of IL-8 receptor expression was shown o n mixed PBL, as identified by using phycoerythrin (PE)-coupled IL-8, a nd this expression was increased following IL-2 stimulation. Scatchard analysis of T cells revealed competitive binding of IL-8 with a K-d o f 0.55 nM, with approximately 1200 receptors per cell, on freshly isol ated T cells. After 24 h in culture following purification, reverse tr anscriptase PCR (RT-PCR) analyses show the mRNA for only the type B IL -8R on these cultured T lymphocytes and the cell line MOLT-4. Stimulat ion of T lymphocytes or T cell clones with IL-8 led to generation of i nositol trisphosphate and calcium flux. In addition, when T cells were prelabeled with [H-3]oleic acid, IL-8 caused a long lasting, time- an d dose-related increase in [H-3] phosphatidylethanol (PtE), indicating activation of phospholipase D (PLD). By contrast, this IL-8-dependent PLD activity was undetectable in IL-8-stimulated neutrophils. PLD act ivation appeared to be downstream of protein kinase C, because several inhibitors abrogated the increase in [H-3]PtE, whereas guanosine-5'-O -(3-thiotriphosphate (GTP(gamma)S) and inositol trisphosphorothioate ( IP3S3) both increased the generation of [H-3]PtE. Together, these resu lts demonstrate that the IL-8RB receptor is sufficient to mediate phos pholipase C (PLC) and PLD activation in T lymphocytes, but not in neut rophils, and indicate an important difference in receptor usage and si gnal transduction pathways between IL-8-stimulated lymphocytes and neu trophils.