Influence of hemolytic and non-hemolytic enterococci on TNF-aexpression in murine macrophage cells

Abstract:

[Objective] To study the influence of hemolytic and non-hemolytic enterococci on TNF-a expression in Murine macrophage cells. [Methods] The possibility of endotoxin contamination in the cell culture was excluded by polymyxin-B inhibition. RAW264.7 were infected with hemolyticor non-hemolytic enerococci at bacteria: cell ratio of 30:1 for 1h, followed by washing and re-incubation for 24h in complete medium containing 200 mg/mL Ampicillin. TNF-a concentrations in culture supernatants at different time intervals after infection for 3 h, 6 h, 9 h and 24 h were measured by ELISA. TNF-a mRNA expression by macrophages infected with hemolytic or non-hemolytic enerococci respectively for 6h was compared by RT-PCR. [Results] TNF-a was not detected in culture supernatants from uninfected RAW264.7 cells. The concentrations (pg/mL) of TNF-a present in culture supernatants from RAW264.7 cells stimulated by hemolytic enterococci were significantly higher than that stimulated by non-hemolytic enterococci at all time intervals tested, p<0.01, Student t-test. TNF-a mRNA expression measured by RT-PCR brought about similar results: more TNF-a mRNA was expressed in RAW 264.7 cells stimulated with hemolytic enterococci as compared with non-hemolytic enterococci stimulation (p<0.05, Student t-test). [Conclusion] hemolytic enterococci promoted the generation of inflammatory factor TNF-a.