Impact of Toll-like receptor signalling on urinary tract infection.

Toll-like receptors (TLRs), components of the innate immune system, play a pivotal role in the pathogenesis of urinary tract infection (UTI). TLRs (especially TLR4) expressed both by epithelial and non-epithelial cells, e.g. monocytes, initiate appropriate immune and inflammatory responses to defend and overcome microbial invasion and infection. Virulent uropathogenic strains (Escherichia coli) express P fimbriae, which bind to glycolipid receptors of uroepithelial and kidney tubular cells, triggering TLR4 activation with subsequent recruitment of leukocytes and release of pro-inflammatory cytokines. Tamm-Horsfall glycoprotein (uromucoid), a kidney-specific glycoprotein, not only binds to fimbriated E. coli and activates complement and dendritic cells, but also apparently shows an immunoregulatory function in UTI via a TLR4-dependent mechanism. Dysregulation of TLR and chemokine candidate genes (e.g. CXCR1) might predispose patients to chronic recurrent UTI. TLR antagonists and agonists can influence host defence mechanisms, and some of these immunomodulating agents may help to overcome intrinsic disturbances of the TLR system to offer new therapeutic options in UTI.