Role of haemolytic and non-haemolytic phospholipase C from Pseudomonas aeruginosa in interleukin-8 release from human monocytes.

A massive accumulation of neutrophils, mainly due to enhanced interleukin-8 (IL-8) levels, is believed to contribute to the deleterious effects of Pseudomonas aeruginosa lung infection, e.g., in cystic fibrosis (CF). Antibodies to phospholipase C, an exoenzyme of P. aeruginosa, are detected early and at high levels in CF patients. However, P. aeruginosa produces at least two types of phospholipase C (PLC), one haemolytic (PLC-H) and the other non-haemolytic (PLC-N), both with mol.wts of c. 77 kDa. Experiments were performed to evaluate the potential contribution of P. aeruginosa PLC to neutrophil accumulation during infection. Therefore, P. aeruginosa PLC-H and PLC-N were compared with regard to IL-8 generation from human monocytes. Purified PLC-H as well as culture supernates (mol.wt > 50 kDa) of a P. aeruginosa strain capable of producing both PLC-H and PLC-N, and mutant strains deficient in the production of one or other phospholipase, or both, were examined. Purified PLC-H (only at low concentrations up to 1 unit/4 x 10(5) monocytes), induced a dose-dependent increase in IL-8 release and IL-8-specific mRNA expression over that of unstimulated cells (at 4-, 12- and 24-h incubation times). Higher concentrations of PLC-H led to a decrease in IL-8 release and IL-8-specific mRNA expression. These findings were confirmed by the results obtained with the supernates of cultures of 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 understanding of the role of both P. aeruginosa PLC in IL-8 generation during their interaction with human monocytes.