The humoral pattern recognition molecule PTX3 is a key component of innate immunity against urinary tract infection.

Immunity in the urinary tract has distinct and poorly understood pathophysiological characteristics and urinary tract infections (UTIs) are important causes of morbidity and mortality. We investigated the role of the soluble pattern recognition molecule pentraxin 3 (PTX3), a key component of the humoral arm of innate immunity, in UTIs. PTX3-deficient mice showed defective control of UTIs and exacerbated inflammation. Expression of PTX3 was induced in uroepithelial cells by uropathogenic Escherichia coli (UPEC) in a Toll-like receptor 4 (TLR4)- and MyD88-dependent manner. PTX3 enhanced UPEC phagocytosis and phagosome maturation by neutrophils. PTX3 was detected in urine of UTI patients and amounts correlated with disease severity. In cohorts of UTI-prone patients, PTX3 gene polymorphisms correlated with susceptibility to acute pyelonephritis and cystitis. These results suggest that PTX3 is an essential component of innate resistance against UTIs. Thus, the cellular and humoral arms of innate immunity exert complementary functions in mediating resistance against UTIs.

Bacterial control of host gene expression through RNA polymerase II.

The normal flora furnishes the host with ecological barriers that prevent pathogen attack while maintaining tissue homeostasis. Urinary tract infections (UTIs) constitute a highly relevant model of microbial adaptation in which some patients infected with Escherichia coli develop acute pyelonephritis, while other patients with bacteriuria exhibit an asymptomatic carrier state similar to bacterial commensalism. It remains unclear if the lack of destructive inflammation merely reflects low virulence or if carrier strains actively inhibit disease-associated responses in the host. Here, we identify a new mechanism of bacterial adaptation through broad suppression of RNA polymerase II­dependent (Pol II­dependent) host gene expression. Over 60% of all genes were suppressed 24 hours after human inoculation with the prototype asymptomatic bacteriuria (ABU) strain E. coli 83972, and inhibition was verified by infection of human cells. Specific repressors and activators of Pol II­dependent transcription were modified, Pol II phosphorylation was inhibited, and pathogen-specific signaling was suppressed in cell lines and inoculated patients. An increased frequency of strains inhibiting Pol II was epidemiologically verified in ABU and fecal strains compared with acute pyelonephritis, and a Pol II antagonist suppressed the disease-associated host response. These results suggest that by manipulating host gene expression, ABU strains promote tissue integrity while inhibiting pathology. Such bacterial modulation of host gene expression may be essential to sustain asymptomatic bacterial carriage by ensuring that potentially destructive immune activation will not occur.

Susceptibility to acute pyelonephritis or asymptomatic bacteriuria: host-pathogen interaction in urinary tract infections.

Our knowledge of the molecular mechanisms of urinary tract infection (UTI) pathogenesis has advanced greatly in recent years. In this review, we provide a general background of UTI pathogenesis, followed by an update on the mechanisms of UTI susceptibility, with a particular focus on genetic variation affecting innate immunity. The innate immune response of the host is critically important in the antibacterial defence mechanisms of the urinary tract, and bacterial clearance normally proceeds without sequelae. However, slight dysfunctions in these mechanisms may result in acute disease and tissue destruction. The symptoms of acute pyelonephritis are caused by the innate immune response, and inflammation in the urinary tract decreases renal tubular function and may give rise to renal scarring, especially in paediatric patients. In contrast, in children with asymptomatic bacteriuria (ABU), bacteria persist without causing symptoms or pathology. Pathogenic agents trigger a response determined by their virulence factors, mediating adherence to the urinary tract mucosa, signalling through Toll-like receptors (TLRs) and activating the defence mechanisms. In ABU strains, such virulence factors are mostly not expressed. However, the influence of the host on UTI severity cannot be overestimated, and rapid progress is being made in clarifying host susceptibility mechanisms. For example, genetic alterations that reduce TLR4 function are associated with ABU, while polymorphisms reducing IRF3 or CXCR1 expression are associated with acute pyelonephritis and an increased risk for renal scarring. It should be plausible to "individualize" diagnosis and therapy by combining information on bacterial virulence and the host response.

Genetics of innate immunity and UTI susceptibility.

A functional and well-balanced immune response is required to resist most infections. Slight dysfunctions in innate immunity can turn the 'friendly' host defense into an unpleasant foe and give rise to disease. Beneficial and destructive forces of innate immunity have been discovered in the urinary tract and mechanisms by which they influence the severity of urinary tract infections (UTIs) have been elucidated. By modifying specific aspects of the innate immune response to UTI, genetic variation either exaggerates the severity of acute pyelonephritis to include urosepsis and renal scarring or protects against symptomatic disease by suppressing innate immune signaling, as in asymptomatic bacteriuria (ABU). Different genes are polymorphic in patients prone to acute pyelonephritis or ABU, respectively, and yet discussions of UTI susceptibility in clinical practice still focus mainly on social and behavioral factors or dysfunctional voiding. Is it not time for UTIs to enter the era of molecular medicine? Defining why certain individuals are protected from UTI while others have severe, recurrent infections has long been difficult, but progress is now being made, encouraging new approaches to risk assessment and therapy in this large and important patient group, as well as revealing promising facets of 'good' versus 'bad' inflammation.

Pathogen specific, IRF3-dependent signaling and innate resistance to human kidney infection.

The mucosal immune system identifies and fights invading pathogens, while allowing non-pathogenic organisms to persist. Mechanisms of pathogen/non-pathogen discrimination are poorly understood, as is the contribution of human genetic variation in disease susceptibility. We describe here a new, IRF3-dependent signaling pathway that is critical for distinguishing pathogens from normal flora at the mucosal barrier. Following uropathogenic E. coli infection, Irf3(-/-) mice showed a pathogen-specific increase in acute mortality, bacterial burden, abscess formation and renal damage compared to wild type mice. TLR4 signaling was initiated after ceramide release from glycosphingolipid receptors, through TRAM, CREB, Fos and Jun phosphorylation and p38 MAPK-dependent mechanisms, resulting in nuclear translocation of IRF3 and activation of IRF3/IFNß-dependent antibacterial effector mechanisms. This TLR4/IRF3 pathway of pathogen discrimination was activated by ceramide and by P-fimbriated E. coli, which use ceramide-anchored glycosphingolipid receptors. Relevance of this pathway for human disease was supported by polymorphic IRF3 promoter sequences, differing between children with severe, symptomatic kidney infection and children who were asymptomatic bacterial carriers. IRF3 promoter activity was reduced by the disease-associated genotype, consistent with the pathology in Irf3(-/-) mice. Host susceptibility to common infections like UTI may thus be strongly influenced by single gene modifications affecting the innate immune response.

Host imprints on bacterial genomes--rapid, divergent evolution in individual patients.

Bacteria lose or gain genetic material and through selection, new variants become fixed in the population. Here we provide the first, genome-wide example of a single bacterial strain's evolution in different deliberately colonized patients and the surprising insight that hosts appear to personalize their microflora. By first obtaining the complete genome sequence of the prototype asymptomatic bacteriuria strain E. coli 83972 and then resequencing its descendants after therapeutic bladder colonization of different patients, we identified 34 mutations, which affected metabolic and virulence-related genes. Further transcriptome and proteome analysis proved that these genome changes altered bacterial gene expression resulting in unique adaptation patterns in each patient. Our results provide evidence that, in addition to stochastic events, adaptive bacterial evolution is driven by individual host environments. Ongoing loss of gene function supports the hypothesis that evolution towards commensalism rather than virulence is favored during asymptomatic bladder colonization.

Toll-like receptor 4 promoter polymorphisms: common TLR4 variants may protect against severe urinary tract infection.

BACKGROUND: Polymorphisms affecting Toll-like receptor (TLR) structure appear to be rare, as would be expected due to their essential coordinator role in innate immunity. Here, we assess variation in TLR4 expression, rather than structure, as a mechanism to diversify innate immune responses. METHODOLOGY/PRINCIPAL FINDINGS: We sequenced the TLR4 promoter (4,3 kb) in Swedish blood donors. Since TLR4 plays a vital role in susceptibility to urinary tract infection (UTI), promoter sequences were obtained from children with mild or severe disease. We performed a case-control study of pediatric patients with asymptomatic bacteriuria (ABU) or those prone to recurrent acute pyelonephritis (APN). Promoter activity of the single SNPs or multiple allelic changes corresponding to the genotype patterns (GPs) was tested. We then conducted a replication study in an independent cohort of adult patients with a history of childhood APN. Last, in vivo effects of the different GPs were examined after therapeutic intravesical inoculation of 19 patients with Escherichia coli 83972. We identified in total eight TLR4 promoter sequence variants in the Swedish control population, forming 19 haplotypes and 29 genotype patterns, some with effects on promoter activity. Compared to symptomatic patients and healthy controls, ABU patients had fewer genotype patterns, and their promoter sequence variants reduced TLR4 expression in response to infection. The ABU associated GPs also reduced innate immune responses in patients who were subjected to therapeutic urinary E. coli tract inoculation. CONCLUSIONS: The results suggest that genetic variation in the TLR4 promoter may be an essential, largely overlooked mechanism to influence TLR4 expression and UTI susceptibility.

A genetic basis of susceptibility to acute pyelonephritis.

BACKGROUND: For unknown reasons, urinary tract infections (UTIs) are clustered in certain individuals. Here we propose a novel, genetically determined cause of susceptibility to acute pyelonephritis, which is the most severe form of UTI. The IL-8 receptor, CXCR1, was identified as a candidate gene when mIL-8Rh mutant mice developed acute pyelonephritis (APN) with severe tissue damage. METHODS AND FINDINGS: We have obtained CXCR1 sequences from two, highly selected APN prone patient groups, and detected three unique mutations and two known polymorphisms with a genotype frequency of 23% and 25% compared to 7% in controls (p<0.001 and p<0.0001, respectively). When reflux was excluded, 54% of the patients had CXCR1 sequence variants. The UTI prone children expressed less CXCR1 protein than the pediatric controls (p<0.0001) and two sequence variants were shown to impair transcription. CONCLUSIONS: The results identify a genetic innate immune deficiency, with a strong link to APN and renal scarring.

Reduced toll-like receptor 4 expression in children with asymptomatic bacteriuria.

Toll-like receptor (TLR) 4 is essential for the defense against infection with gram-negative pathogens, but reduced TLR4 expression has not been linked to altered disease susceptibility in humans. In mice, Tlr4 controls the mucosal response to Escherichia coli urinary tract infections. Inactivation of mouse Tlr4 causes an asymptomatic carrier state resembling asymptomatic bacteriuria (ABU). The present study compared neutrophil TLR4 expression levels between children with ABU (n=17) and age-matched control subjects (n=24), and significantly lower levels were detected in the patients with ABU. We also found elevated levels of the TLR4 adaptor protein TRIF and reduced levels of the TLR4-inhibitor SIGIRR in the patients with ABU, but MyD88 and TRAM levels were not significantly altered. Altered TLR4 and adaptor protein expression might impair TLR4 signaling and explain the weak mucosal response to urinary tract infection in patients who develop ABU rather than symptomatic disease.

Inherited susceptibility to acute pyelonephritis: a family study of urinary tract infection.

BACKGROUND: Urinary tract infections (UTIs) are important causes of morbidity and death. The present study investigated whether genetic factors influence susceptibility to acute pyelonephritis (APN). CXCR1 expression was investigated as a factor predisposing to APN, because low CXCR1 expression has been associated with disease susceptibility in mice and disease-prone children. METHODS: The families of APN-prone children (n=130) and of age-matched control subjects without UTI (n=101) were studied. Three-generation pedigrees of UTI-associated morbidity were established by means of structured interviews of the families. CXCR1 expression was quantified by flow cytometric analysis of peripheral blood neutrophils obtained from family members and control subjects. RESULTS: APN was significantly more common in the family members of the APN-prone children (20 [15%] of 130 family members) than in the relatives of the control subjects (3 [3%] of 101 family members) (P<.002). Acute cystitis, in contrast, occurred with equal frequency in both groups (19%; P=1.0). Some families included many affected individuals, consistent with a dominant pattern of inheritance, whereas other families showed a recessive pattern of disease susceptibility. CXCR1 expression was significantly lower in the APN-prone children and in their relatives than in pediatric and adult control subjects (P<.0001). CONCLUSIONS: Our results suggest that susceptibility to APN is inherited and that low CXCR1 expression might predispose to disease.

Uropathogenic Escherichia coli as a model of host-parasite interaction.

Resistance to mucosal infection varies greatly in the population, but the molecular basis of disease susceptibility is often unknown. Studies of host-pathogen infections are helpful to identify virulence factors, which characterise disease isolates, and successful defence strategies of hosts that resist infection. In the urinary tract infection (UTI) model, we have identified crucial steps in the pathogen-activated innate host response, and studied the genetic control of these activation steps. Furthermore, genetic variation in the innate host-response defence is investigated as a basis of disease susceptibility. The Toll-like receptor 4 (TLR4) controls initial mucosal response to uropathogenic Escherichia coli (UPEC). Bacterial TLR4 activation in epithelial cells leads to chemokine secretion and neutrophil recruitment and TLR4 mutant mice develop an asymptomatic carrier state. The chemokine receptor CXCR1 determines the efficiency of neutrophil migration and activation, and thus of bacterial clearance. CXCR1 mutant mice become bacteremic and develop renal scars and studies in UTI prone children have detected low CXCR1 expression, suggesting that CXCR1 is also essential for human disease susceptibility.