Fimbrial Protein FimH Is Involved in Expression of Proinflammatory Cytokines in a Toll-Like Receptor 4-Dependent Manner.

Type 1 fimbriae are proteinaceous filamentous structures present on bacterial surfaces and are mainly composed of the major fimbrial protein subunit FimA and the adhesive protein FimH, which is located at the tip of the fimbrial shaft. Here, we investigated the involvement of type 1 fimbriae in the expression of proinflammatory cytokines in macrophages infected with serovar Typhimurium. The level of interleukin-1β (IL-1β) mRNA was lower in macrophages infected with or mutant strains than in those infected with wild-type Treatment of macrophages with purified recombinant FimH protein, but not FimA, resulted in the activation of the mitogen-activated protein kinase and nuclear factor κB signaling pathways, leading to the expression of not only IL-1β but also other proinflammatory cytokines, such as IL-6 and tumor necrosis factor alpha.