ROLE OF HEMOLYTIC AND NONHEMOLYTIC PHOSPHOLIPASE-C FROM PSEUDOMONAS-AERUGINOSA IN INTERLEUKIN-8 RELEASE FROM HUMAN MONOCYTES

A massive accumulation of neutrophils, mainly due to enhanced interleu kin-8 (IL-8) levels, is believed to contribute to the deleterious effe cts of Pseudomonas aeruginosa lung infection, e.g., in cystic fibrosis (CF). Antibodies to phospholipase C, an exoenzyme of P. aeruginosa, a re detected early and at high levels in CF patients. However, P. aerug inosa produces at least two types of phospholipase C (PLC), one haemol ytic (PLC-H) and the other non-haemolytic (PLC-N), both with mol. wts of c. 77 kDa. Experiments were performed to evaluate the potential con tribution of P. aeruginosa PLC to neutrophil accumulation during infec tion. Therefore, P. aeruginosa PLC-H and PLC-N were compared with rega rd to IL-8 generation from human monocytes. Purified PLC-H as well as culture supernates (mol. wt > 50 kDa) of a P. aeruginosa strain capabl e of producing both PLC-H and PLC-N, and mutant strains deficient in t he production of one or other phospholipase, or both, were examined. P urified PLC-H (only at low concentrations up to 1 unit/4 X 10(5) monoc ytes), induced a dose-dependent increase in IL-8 release and IL-8-spec ific mRNA expression over that of unstimulated cells (at 4-, 12- and 2 4-h incubation times), Higher concentrations of PLC-H led to a decreas e in IL-8 release and IL-8 specific mRNA expression. These findings we re confirmed by the results obtained with the supernates of cultures o f mutant strains of P. aeruginosa PAO1 that produced either a PLC-H or PLC-N or neither, Stimulation and inhibition of IL-8 release and mRNA expression were associated with a culture supernate fraction of mol. wt > 50 kDa and containing PLC-H, These results contribute to the unde rstanding of the role of both P. aeruginosa PLC in IL-8 generation dur ing their interaction with human monocytes.