EFFECT OF PSEUDOMONAS-AERUGINOSA ON INTERLEUKIN-8 RELEASE FROM HUMAN PHAGOCYTES

Pseudomonas aeruginosa infections are commonly observed in sepsis, burns, as well as cystic fibrosis (CF). Among the professional phagocytes neutrophils and monocytes are recruited by various chemotactic factors from the cellular environment. Although they provide the first line of host defense excessive neutrophil accumulation seems to be a major cause of pathogenesis during P. aeruginosa infection. Interleukin-8 (IL-8) represents one important chemoattractant for professional phagocytes. To evaluate IL-8 releasability by phagocytes in the context of P. aeruginosa infection and especially of CF, we stimulated human polymorphonuclear neutrophilic granulocytes (PMN) and peripheral blood mononuclear cells (PBMC) as a source for monocytes with clinical P. aeruginosa isolates, with mucoid P. aeruginosa strain (CF3M) and its nonmucoid revertant (CF3), and with purified P. aeruginosa mucoid exopolysaccharide (alginate). A significant increase in IL-8 release as compared to unstimulated cells was observed after an incubation time of 90 min for PMN and after 60 min for PBMC which increased (PMN: up to 60-fold; PBMC: up to 40-fold) over time (up to 4 h). In contrast of PBMC, when PMN were studied, intracellular IL-8 exceeded the IL-8 release in unstimulated as well as in stimulated cells by up to 10-fold. All clinical P. aeruginosa isolates, independent of the clinical source, induced IL-8 release from human PBMC and PMN in a dose- and time-dependent manner. Bacteria of strain CF3M induced similar amounts of IL-8 release from human PMN and PBMC as compared to bacteria of strain CF3; optimal IL-8 release was obtained at a bacteria to cell ratio of 43:1 for PMN and 6:1 for PBMC. Purified alginate from two different mucoid P. aeruginosa strains (CF3M; AL3) led to a slight but significant induction of IL-8 release from human PMN and PBMC, by maximally 4- to 6-fold from human PMN and PBMC after 120 min of incubation, while alginate from algae (kelpalginate) failed to do so. We conclude from the above data that (1) P. aeruginosa bacteria induce IL-8 release from professional phagocytes (granulocytes, monocytes) and thus are able to amplify or perpetuate the acute inflammatory response by recruiting additional phagocytes into an inflammatory site, and (2) the release of IL-8 from phagocytes is not inhibited by P. aeruginosa alginate.