Interleukin-8-stimulated polyphosphoinositide hydrolysis in human peripheral blood lymphocytes

We have attempted to provide evidence for the production of inositol phosphate (IP) metabolites as an indication of specific receptor-mediated signal transduction in human peripheral blood lymphocytes (PBL) in response to interleukin-8 (IL-8). IP metabolites were measured, after loading of PBL with [3H]-D-myo-inositol, by anion exchange high-performance liquid chromatography (HPLC) and liquid scintillation counting of collected fractions. In addition, inositol-1,4,5-trisphosphate (IP3), in extracts from unlabeled cells, was measured using a specific radioligand binding assay. Compared with phytohemagglutinin (PHA), which stimulated an increase in IP metabolites and, specifically, IP3 by greater than threefold, human recombinant (hr) IL-8 (1 nmol/L) also stimulated an increase in IP metabolites, as measured by HPLC, and a greater than threefold increase in IP3. The increase in IP3 was observed as early as 15 seconds after stimulation with hrIL-8, reaching maximal levels by 30 seconds. To further assess the signal transduction mechanism involved, the protein tyrosine kinase inhibitor genistein was added to the cells 10 minutes before stimulation with hrIL-8. After preincubation of PBL with this inhibitor, the generation of IP3 in response to PHA (5 micrograms/mL) and hrIL-8 (1 nmol/L) was inhibited by 42% and 51% of control values, respectively. In contrast to the production of IP metabolites, there were only small increases in intracellular calcium in response to hrIL-8 when compared with PHA.