Abstract: 【Objective】Lactobacillus rhamnosus (L. rhamnosas) was examined for its capacity to facilitate the innate immune responses of macrophage cell in vitro in terms of innate immune factor production. 【Method】 The murine macrophage cell line, RAW 264. 7, was treated with PBS (designated as group CT, control group), Escherichia coli K88（designated as group EC）and L. rhamnosus（designated as group LR）for 12 h，respectively, as well as treated with L. rhamnosus prior for 1 h, and then exposed to E. coli K88 for 12 h（designated as group LR-EC）. After incubation, culture supernatants were collected for further analysis of TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-8, IL-10, PGE2 and   using ELISA. 【Result】Results showed that TNF-α, IFN-γ, IL-8 and IL-10 production was observed in group CT (the control group)，whereas the concentrations of IL-1β, IL-6 and IL-12 were below the detection limits. Production of TNF-α, IFN-γ, IL-8, IL-10, PGE2 and   in group EC increased significantly（P＜0.01）compared to group CT, and higher concentrations of IL-1β, IL-6 and IL-12 were also detectd in group EC. Higher levels of TNF-α, IFN-γ, IL-10, PGE2,     （P＜0.01）and IL-8（P＜0.05）were determined in group LR while no detectable effect on IL-1β and IL-6 was found. Moreover,  the release of all tested proinflammatory cytokines（TNF-α, IFN-γ, IL-1β, IL-6, IL-12）, chemotactic factor (IL-8) and PGE2 in  group LR-EC was up-regulated remarkably（P＜0.01）while secretion of IL-10 and   was noticeably suppressed in comparison to group EC（P＜0.01）. 【Conclusion】 It was concluded that probiotics strain L. rhamnosus is capable of triggering a moderate innate immune response on direct contact with murine macrophage cell line RAW264.7. Furthermore, L. rhamnosus could enhance proinflammatory response to infected macrophages; meanwhile, it might prevent excessive inflammatory reaction in vitro.

Key words: RAW264.7 cell, Lactobacillus rhamnosus, Escherichia coli K88, cytokine, chemotactic factor, PGE2