Immunological effects of probiotic strain Enterococcus faecium EF1 was evaluated through the production of cytokines, superoxide anion (O₂^.-) and prostaglandin E₂ (PGE₂) in murine macrophage cell line RAW 264.7. In addition, the responses were contrasted with a pathogenic coliform, Escherichia coli strain K88. After 12-h co-incubation of RAW 264.7 with E. faecium EF1 or E. coli K88, the culture supernatants were collected for further analysis of cytokines (TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-8 and IL-10) and inflammatory mediators including superoxide anion (O₂^.-) and PGE₂. The results showed that, E. faecium EF1 induced an increased (P<0.01) release of TNF-α, IFN-γ, IL-6, IL-10 and O₂^.- in RAW 264.7 cells. However, levels of cytokines induced by E. faecium EF1 were far lower (P<0.01) than those observed following co-culture with E. coli K88. In addition, when RAW 264.7 cells were first treated with E. faecium EF1 and then infected with E. coli K88, the production of IL-12 and O₂^.- in response to E. coli K88 were significantly suppressed, indicating that E. faecium EF1 may limit the ability of macrophages to induce excessive inflammation even to potent inflammatory bacteria. Our current findings concluded that, E. faecium EF1 was capable of triggering a moderate innate inflammatory response on direct contact with murine macrophage cell line RAW264.7.

Key words: Cytokine, Enterococcus faecium, Prostaglandin E_2, Superoxide anion