[Investigation of bactericidal effect and nitric oxide responses of Caco-2 epithelial cells and THP-1 macrophage cells against Streptococcus pyogenes and Escherichia coli].

: Epithelial cells and macrophages contribute to innate immune responses by cell to cell interactions and releasing proinflammatory mediators. In this study, we aimed to illuminate the underlying mechanisms of contribution of macrophages and epithelial cells in the struggle against pathogens. Therefore, Streptococcus pyogenes and Escherichia coli activated Caco-2 cells and THP-1 macrophage-like cells were investigated for their bactericidal activities and nitric oxide (NO) production when they were alone, in contact with eachother and when their contact was blocked by continuing exposure of soluble mediators. Caco-2 epithelial cells and THP-1 macrophage cells were used as effector cells and S. pyogenes or E. coli as target cells and were incubated at an effector cell/target cell ratio of 1/1 in duplication in 24-well plates. After 5 hours incubation, supernatants were collected from each well for growth inhibition assay and were inoculated onto blood agar plates for S. pyogenes and eosin methylene blue agar plates for E. coli. Following overnight incubation at 37 degrees C, bactericidal effect rate was calculated by counting the colony forming units. The supernatants were also collected after 5 and 24 hours incubation for measurement of NO production by using Griess reagent. Bactericidal effect of Caco-2 cells alone against S. pyogenes and E. coli were found 21.9% and 36.2%, when seperated from THP-1 cells via an insert was 31.8% and 30.5%, and when cell-cell contact was established with THP-1 cells was 24.4% and 55.7%, respectively. Bactericidal effect of THP-1 cells alone against S. pyogenes and E. coli was 27.7% and 63.9%, when seperated from Caco-2 cells via an insert was %27.5 and 43.6%, and when cell-cell contact was established with Caco-2 cells was 24.4% and 55.7%, respectively. As a result, we found that Caco-2 epithelial cells and THP-1 macrophage cells had an antibacterial effect against S. pyogenes and E. coli (p < 0.05), and this effect was higher in macrophage cells than epithelial cells. NO levels in epithelial and/or macrophage cell culture supernatants collected after exposure to S. pyogenes and E. coli were significantly higher for S. pyogenes at 5 hours incubation and for E. coli at 24 hours incubation (p < 0.05). Morever, it can be concluded that macrophages played a more active role than epithelial cells in bactericidal effect and NO response. Besides, epithelial cells and macrophages activated each other more when they were in contact than when they were alone or when their contact was blocked.