Escherichia coli flagellin stimulates pro-inflammatory immune response

Flagellin, a principal component of bacterial flagella, is a virulence factor that is recognized by the innate immune system. Recognition of flagellin by innate immune receptors stimulates the production of cytokines necessary for the development of effective immunity. Here, we demonstrated that the intranasal (i.n.) instillation of different amount of Escherichia coli K-12 flagellin preparation (0.5, 1, 2, 4 μg) in BALB/c mice induced pro-inflammatory immune response. Instillation i.n. of 1 μg of flagellin induced the maximum expression of interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) mRNA and production of pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) in mice lungs. The same dose of flagellin induced neutrophil polymorphonuclear cells infiltration in peribronchial and perivascular regions. High number of neutrophil in bronchoalveolar lavage fluid was found at 24 h after i.n. instillation of flagellin (1 μg). These findings were concomitant with the maximum production of myeloperoxidase and nitric oxide in mice lungs. Present study showed that the maximum pro-inflammatory mediator levels were found when mice instilled i.n. with 1 μg E. coli flagellin. The amount of flagellin of E. coli K-12 that achieve the maximum stimulation of mucosal pro-inflammatory immune response in mice lungs was explored in this study.