Innate immune responses to Proteus mirabilis flagellin in the urinary tract

Flagella are bacterial virulence factors allowing microorganisms to move over surfaces. Flagellin, the structural component of flagella, is sensed by the host via Toll and NOD-like receptors and triggers pro-inflammatory responses. The use of Toll-like receptors agonists to modulate innate immune responses has aroused great interest as an alternative to improve the treatment of diverse infectious diseases. Proteus mirabilis is a Gram negative bacterium that causes urinary tract infections in humans. In the present work we used different approaches to study the ability of P. mirabilis flagellin to induce an innate immune response. We demonstrated that P. mirabilis flagellin has the ability to induce pro-inflammatory chemokines expression in T24 bladder cultures cells and in the mouse bladder after instillation. It was evidenced also that flagellin from different P. mirabilis strains differed in their capacity to induce an innate immune response in the CacoCCL20-Luc system. Also, flagellin elicited inflammation, with recruitment of leukocytes to the bladder epithelium. Flagellin instillation before an experimental P. mirabilis infection showed that the inflammatory response due to flagellin did not help to clear the infection but favored bacterial colonization. Thus, induction of inflammatory response in the bladder did not contribute to P. mirabilis infection neutralization.