Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Urinary tract infections (UTI) frequently progress to chronicity in infected individuals but the mechanisms of pathogenesis underlying chronic UTI are not well understood. We examined the role of interleukin (IL)-17A in UTI because this cytokine promotes innate defense against uropathogenic Escherichia coli (UPEC). Analysis of UPEC persistence and pyelonephritis in mice deficient in IL-17A revealed that UPEC CFT073 caused infection at a rate higher than the multidrug resistant strain EC958. Il17a −/− mice exhibited pyelonephritis with kidney bacterial burdens higher than those of wild-type (WT) mice. Synthesis of IL-17A in the bladder reflected a combination of γδ-T and T H 17 cell responses. Analysis of circulating inflammatory mediators at 24h postinoculation identified predictors of progression to chronicity, including IL-6 and monocyte chemoattractant protein-1 (MCP-1). Histological

Interleukin-10 is part of the immune response to urinary tract infection (UTI) due to E. coli, and it is important in the early control of infection in the bladder. Defining the mechanism of engagement of the immune system by the bacteria that enables the protective IL-10 response is critical to exploring how we might exploit this mechanism for new infection control strategies. In this study, we reveal part of the bacterial flagellar apparatus (FliC) is an important component that is sensed by and responsible for induction of IL-10 in the response to UPEC. We show this response occurs in a TLR5-dependent manner. Using infection prevention and control trials in mice infected with E. coli, this study also provides evidence that purified FliC might be of value in novel approaches for the treatment of UTI or in preventing infection by exploiting the FliC-triggered bladder transcriptome.

Uropathogenic Escherichia coli (UPEC) cause the majority of community-acquired urinary tract infections (UTIs). Quantitation of bacteriuria (the number of bacteria in urine) is important for diagnostic approaches and in diverse research applications. Most UPEC strains express hemolysin, the expression of which has been correlated with the severity of UTI in murine models of infection. In this study, we sought to develop and optimise a quantitative Polymerase Chain Reaction (qPCR) assay for enumeration of hemolysin-positive UPEC in urine. Using recombinant plasmid pJET1.2::hlyD, which we termed pGU2470, the sensitivity range and linearity of amplification of qPCR was determined using primers and a probe targeting hlyD. Whole-cell preparations containing UPEC were quantified for hlyD copy number using C values and compared to standards prepared with a known amount of pGU2470. We compared the efficiency of the assay for analysis of human and mouse urine because mouse models of human UTI are frequently used for investigating UPEC UTI. Urine samples were collected from healthy adults and mouse infection assays and used to assess any potential inhibitory effects of urine on the qPCR. The linear quantitative range of the qPCR (i.e. sensitivity) in detecting UPEC genomes was 10 copies/ml; qPCR-derived estimates of UPEC bacteriuria (based on number of genomes detected) were, on average, ten-fold higher that culture-based estimates. Finally, the frequencies of positive and negative predictions of UPEC in urine using the qPCR were equivalent to colony count methods. This assay provides an alternative to culture-based approaches for quantitation of UPEC bacteriuria in research studies.

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