Extracellular product of Pseudomonas aeruginosa in growth medium is involved in the pro-inflammatory cytokine response of human oral epithelial cells in vitro.

Abstract

Epithelial cells are the first barrier to any microbial invasion. Finding a safe and affordable substance to stimulate the innate immune response of epithelial cells is one of the main challenges immunologists and vaccine manufacturers are facing. This study aimed to show the comparative effect of sterile bacterial secretion (SBS) and Pseudomonas aeruginosa bacterial cell isolates obtained from burn wound infections on the ability of human epithelial cells (HECs) to produce interleukin (IL)-1β and tumor necrosis factor alpha (TNF-α) in vitro. The HEC cultures were exposed to P. aeruginosa 8 (Pa 8), Pa 2 and Pa 1 bacterial cells (isolated from burn wound infections). The other 3 groups of HECs were exposed to 50 μL of sterile, endotoxin-free SBS of Pa 8, Pa 2 and Pa 1. The time course of changes in IL-1β mRNA, TNF-α mRNA, IL-1β, and TNF-α was examined. Moderate (p < 0.05) elevations of IL-1β mRNA in HECs and IL-1β protein in the supernatant of the HEC culture were observed following exposure to SBS of Pa 8, Pa 2 and Pa 1 at most time points. High elevation (p < 0.05) of IL-1β was seen in the supernatant of the HEC culture that was exposed to bacterial cells (Pa 8, Pa 2 and Pa 1). Similar results were found when TNF-α mRNA was measured in HECs and TNF-α in the supernatant of the HEC cultures after exposure to bacterial cells (Pa 8, Pa 2 and Pa 1) and the SBS of Pa 8, Pa 2 and Pa 1. This is the first time that the capacity of SBS to generate epithelial cell pro-inflammatory cytokines in vitro has been shown. In other words, SBS enhanced a nonspecific immune response, which opens the door to the possibility of using SBS from P. aeruginosa as an adjuvant in the future.