Abstract
Interleukin-8 (IL-8) participates in the generation of dense neutrophil accumulations in bronchopulmonary infections caused by Pseudomonas aeruginosa (P. aeruginosa). We have recently reported that nitrite reductase, a bifunctional enzyme located in the periplasmic space of P. aeruginosa, induces IL-8 generation in bronchial epithelial cells (K. Oishi et al. Infect. Immun. 65: 2648-2655, 1997). We examined whether or not Pseudomonas nitrite reductase (PNR) could also stimulate human alveolar macrophages (AM) and pulmonary type II epithelial-like cells (A549) to induce IL-8 production and mRNA expression as well as the production of TNFα and IL-1β. We demonstrated a time- and dose-dependent IL-8 protein synthesis and IL-8 mRNA expression, but no TNFα or IL-1β production, by A549 cells in response to PNR. New protein translation was not required for PNR-mediated IL-8 mRNA expression in the same cells. Furthermore, simultaneous stimulation of PNR with serial doses of TNFα or IL-1β resulted in additive IL-8 production in A549 cells. In adherent AM, PNR enhanced IL-8 protein synthesis and IL-8 mRNA expression in a time-dependent fashion. PNR similarly induced a time-dependent production of TNFα and IL-1β by human adherent AM. Neutralization of TNFα or IL-1β did not influence the levels of IL-8 production in adherent AM culture. We also evaluated whether the culture supernatants of the A549 cells or AM stimulated with PNR could similarly mediate neutrophil migration in vitro. When anti-human IL-8 immunoglobulin G was used for neutralizing neutrophil chemotactic factor (NCF) activities in the culture supernatants of these cells stimulated with 5μg/ml of PNR, the mean percent reduction of NCF activities were 49-59% in A549 cells and 24-34% in AM. Our present data support that PNR directly stimulates AM and pulmonary epithelial cells to produce IL-8. PNR also mediates neutrophil migration, in part, through IL-8 production from AM and pulmonary epithelial cells. These data suggest the contribution of PNR to the pathogenesis of bronchopulmonary infections due to P. aeruginosa.
