Minireview: functions of the renal tract epithelium in coordinating the innate immune response to infection

Innate immunity and urinary tract infection

Urinary tract infections are a severe public health problem. The emergence and spread of antimicrobial resistance among uropathogens threaten to further compromise the quality of life and health of people who develop acute and recurrent upper and lower urinary tract infections. The host defense mechanisms that prevent invasive bacterial infection are not entirely delineated. However, recent evidence suggests that versatile innate immune defenses play a key role in shielding the urinary tract from invading uropathogens. Over the last decade, considerable advances have been made in defining the innate mechanisms that maintain immune homeostasis in the kidney and urinary tract. When these innate defenses are compromised or dysregulated, pathogen susceptibility increases. The objective of this review is to provide an overview of how basic science discoveries are elucidating essential innate host defenses in the kidney and urinary tract. In doing so, we highlight how these findings may ultimately translate into the clinic as new biomarkers or therapies for urinary tract infection.

Urinary antimicrobial peptides: Potential novel biomarkers of obstructive uropathy

INTRODUCTION

Antimicrobial peptides (AMPs) have historically been evaluated for their role in protecting against uropathogens. However, there is mounting evidence to support their expression in noninfectious injury, with unclear meaning as to their function. It is possible that AMPs represent urothelial injury. Urinary tract obstruction is known to alter the urothelium; however, AMPs have not been evaluated for expression in this noninfectious injury.

OBJECTIVE

A pilot study to compare urinary AMP expression in children undergoing surgical intervention for ureteropelvic junction obstruction (UPJO) with nonobstructed controls.

STUDY DESIGN

Bladder urine was collected from consenting/assenting pediatric patients with UPJO at intervention. Control bladder urines were obtained from age-matched and sex-matched healthy children without known obstruction or infection. Enzyme-linked immunosorbent assays were run for the following AMPs: β defense 1 (BD-1), neutrophil gelatinase-associated lipocalin (NGAL), cathelicidin (LL-37), hepatocarcinoma-intestine-pancreas/pancreatitis-associated protein (HIP/PAP), and human α defensin 5 (HD-5); and normalized to urine creatinine. Results were analyzed with Student's t-test or Mann-Whitney U test, when appropriate, and receiver operating characteristic curves. A P-value of <0.05 was considered significant.

RESULTS

Thirty bladder urine samples were obtained from children with UPJO at the time of decompressive intervention. Mean patient age was 4.7 years (range 0.3-18.4); 20 (67%) patients were male. Fifteen bladder urine samples were obtained from age-matched and sex-matched controls. Urinary AMP levels were significantly higher in UPJO patients than controls for BD-1 (P = 0.015), NGAL (P < 0.001), LL-37 (P < 0.001), and HIP/PAP (P = 0.046). Optimal threshold values of these AMPs were determined, with each demonstrating significant odds ratios of predicting urinary obstruction.

DISCUSSION

Certain urinary AMPs are altered even in noninfectious urinary tract pathology. This represents a novel induction of AMP expression, as the current study is the first to report elevations in BD-1 and HIP/PAP in urinary tract obstruction. This suggests other roles for these AMPs outside of their antimicrobial properties, and likely is a reflection of the urothelial and tubular stress resulting from obstructive uropathy.

CONCLUSIONS

Induction of AMPs BD-1, NGAL, LL-37, and HIP/PAP was found to occur in urinary tract obstruction. Further evaluation of AMP expression as a biomarker of uroepithelial injury outside of infection is indicated.

Impact of cytokine genetic polymorphisms on the risk of renal parenchymal infection in children

BACKGROUND

Acute pyelonephritis is associated with renal scarring in up to 30% of patients. Renal scarring may cause significant long-term morbidity. The pathogenesis of acute pyelonephritis remains unclear, although it involves interaction among uroepithelium, the immune system cells, and the locally produced cytokines. That some UTI-prone children develop acute pyelonephritis, and eventually renal parenchymal scarring, suggests a genetic role. Interleukin-6, interleukin-8, chemokine receptor-1 (CXCR1), and tumor necrosis factor-alpha (TNFα), the key regulators of the host immune responses, are proteins whose secretion is controlled by genes. We postulated that functional polymorphic variants of their genes might have a role in APN susceptibility.

OBJECTIVES

We sought to investigate a possible association of the common functional polymorphisms in genes encoding IL-6, IL-8, CXCR1, and TNFα with the risk of APN in children.

METHODS

Urine culture was used to diagnose 300 children with UTI, of mean age of 51.31 ± 37.4 months (2-180 months). 99Tc-DMSA scans diagnosed 86 children with APN. Follow-up scans identified new renal scars in 18 children. Six functional single-nucleotide polymorphisms (SNPs) in genes encoding IL-6, IL-8, CXCR1, and TNFα were genotyped in all subjects (IL-6 rs1800795 (-174G/C), IL-6 rs1800796 (-572G/C), IL-8 rs2227306 (781C/T), IL8 rs4073 (-251A/T), CXCR1 rs2234671 (2607G/C), and TNFα rs1800629 (-308G/A)).

RESULTS

TT genotype of IL-8 -251A/T polymorphism was significantly higher in APN patients (26.7%) than those with lower UTI (11.7%, p = 0.01) and control individuals (12.2%, p = 0.002). T allele was significantly more common in APN than in lower UTI (p = 0.025) and was significantly more common in APN (46%) than in the controls (p = 0.001). Similarly, TT genotype of IL-8 781C/T polymorphism was significantly more common in APN patients (31.4%) than those with lower UTI (17.3%, p = 0.003) and the controls (14.3%, p = 0.001). T allele was significantly more common in APN (55%) than lower UTI (40%, p = 0.005) and controls (37%, p = 0.001). However, IL-8 -251A/T and +781C/T SNPs did not qualify as an independent risk for parenchymal infection (OR 1.9, 95% CI 0.68-2.6, p = 0.13 and OR 2.3, 95% CI 0.89-3.7, p = 0.091, respectively). Lower UTI did not differ from the controls. The frequency of the genotypes and alleles of IL-6, CXCR1, and TNFα SNPs did not differ significantly among the different groups of the study.

CONCLUSION

IL-8 -251A/T and +781C/T SNPs are associated with susceptibility to renal parenchymal infection in children and could be implicated in APN risk. However, none of these variants could clearly and independently predict this risk.

The clinical diagnosis and management of urinary tract infections in children and adolescents

Urinary tract infections (UTI) are one of the most common and serious bacterial infections encountered by paediatricians and primary care physicians. Although the diagnosis and management of UTI appear simplistic, they remain among the most contentious issues in paediatrics. In part, UTI controversies stem from the absence of classic clinical symptoms, inappropriate urine specimen collection, modified urinary tract imaging recommendations, and diverse treatment and prevention strategies. Recently published guidelines and large clinical trials have attempted to clarify UTI diagnostic and management strategies. In this manuscript, we review the diagnosis and management of acute and recurrent UTI in the paediatric and adolescent populations.

Susceptibility to Urinary Tract Infection: Benefits and Hazards of the Antibacterial Host Response

A paradigm shift is needed to improve and personalize the diagnosis of infectious disease and to select appropriate therapies. For many years, only the most severe and complicated bacterial infections received more detailed diagnostic and therapeutic attention as the efficiency of antibiotic therapy has guaranteed efficient treatment of patients suffering from the most common infections. Indeed, treatability almost became a rationale not to analyze bacterial and host parameters in these larger patient groups. Due to the rapid spread of antibiotic resistance, common infections like respiratory tract- or urinary-tract infections (UTIs) now pose new and significant therapeutic challenges. It is fortunate and timely that infectious disease research can offer such a wealth of new molecular information that is ready to use for the identification of susceptible patients and design of new suitable therapies. Paradoxically, the threat of antibiotic resistance may become a window of opportunity, by encouraging the implementation of new diagnostic and therapeutic approaches. The frequency of antibiotic resistance is rising rapidly in uropathogenic organisms and the molecular and genetic understanding of UTI susceptibility is quite advanced. More bold translation of the new molecular diagnostic and therapeutic tools would not just be possible but of great potential benefit in this patient group. This chapter reviews the molecular basis for susceptibility to UTI, including recent advances in genetics, and discusses the consequences for diagnosis and therapy. By dissecting the increasingly well-defined molecular interactions between bacteria and host and the molecular features of excessive bacterial virulence or host-response malfunction, it is becoming possible to isolate the defensive from the damaging aspects of the host response. Distinguishing "good" from "bad" inflammation has been a long-term quest of biomedical science and in UTI, patients need the "good" aspects of the inflammatory response to resist infection while avoiding the "bad" aspects, causing chronicity and tissue damage.

Does the presence of vesicoureteral reflux affect in vitro uropathogenic E. coli growth rate in urine?

BACKGROUND

Uroepithelial molecules like uroplakins are involved both in the development of urinary tract and in colonization, attachment and invasion of uropathogenic Escherichia coli (UPEC). Uroplakin disorders are also associated with vesicoureteral reflux (VUR). We hypothesized that urine contents, as well as urinary flow, may be altered in VUR, and aimed to determine whether in vitro UPEC growth is increased in urine from the refluxing systems.

METHODS

Children evaluated by voiding cystourethrography for UTI were enrolled. Groups 1 and 2 included children with and without VUR, respectively. Sterile urine samples were obtained from all patients, and 2 × 10(2) cfu/mL UPEC suspension was inoculated into these samples. After incubation for 24 h, colony counts were assessed. Both groups were compared for UPEC growth and colony counts.

RESULTS

Forty-two urine samples were included (21 in each group). UPEC was cultured in 9 (43 %) and 3 (14 %) samples in Groups 1 and 2, respectively (p = 0.040, OR 4.5). Colony counts were similar in both groups (log x; 2.36 ± 0.25 vs. 2.37 ± 0.12, p = 0.923).

CONCLUSION

Inoculation of 2 × 10(2) cfu UPEC resulted in growth in almost half of the urine samples from refluxing systems, while UPEC growth was inhibited in most urine samples from non-refluxing systems suggesting that urine contents in refluxing units change in such a way that UPEC growth is facilitated.

A metaproteomics approach to elucidate host and pathogen protein expression during catheter-associated urinary tract infections (CAUTIs)

Long-term catheterization inevitably leads to a catheter-associated bacteriuria caused by multispecies bacterial biofilms growing on and in the catheters. The overall goal of the presented study was (1) to unravel bacterial community structure and function of such a uropathogenic biofilm and (2) to elucidate the interplay between bacterial virulence and the human immune system within the urine. To this end, a metaproteomics approach combined with in vitro proteomics analyses was employed to investigate both, the pro- and eukaryotic protein inventory. Our proteome analyses demonstrated that the biofilm of the investigated catheter is dominated by three bacterial species, that is, Pseudomonas aeruginosa, Morganella morganii, and Bacteroides sp., and identified iron limitation as one of the major challenges in the bladder environment. In vitro proteome analysis of P. aeruginosa and M. morganii isolated from the biofilm revealed that these opportunistic pathogens are able to overcome iron restriction via the production of siderophores and high expression of corresponding receptors. Notably, a comparison of in vivo and in vitro protein profiles of P. aeruginosa and M. morganii also indicated that the bacteria employ different strategies to adapt to the urinary tract. Although P. aeruginosa seems to express secreted and surface-exposed proteases to escape the human innate immune system and metabolizes amino acids, M. morganii is able to take up sugars and to degrade urea. Most interestingly, a comparison of urine protein profiles of three long-term catheterized patients and three healthy control persons demonstrated the elevated level of proteins associated with neutrophils, macrophages, and the complement system in the patient's urine, which might point to a specific activation of the innate immune system in response to biofilm-associated urinary tract infections. We thus hypothesize that the often asymptomatic nature of catheter-associated urinary tract infections might be based on a fine-tuned balance between the expression of bacterial virulence factors and the human immune system.

The diagnosis, evaluation and treatment of acute and recurrent pediatric urinary tract infections

Urinary tract infection (UTI) is one of the most common bacterial infections encountered by pediatricians. Currently, the diagnosis and management of acute UTI and recurrent UTI in children remain controversial. Recently published guidelines and large clinical trials have attempted to clarify UTI diagnostic and management strategies. In this manuscript, we review the diagnosis and management of acute and recurrent UTI in the pediatric population.

Pseudomonas quinolone signalling system: a component of quorum sensing cascade is a crucial player in the acute urinary tract infection caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen which employs quorum sensing system to regulate several genes required for its survival and pathogenicity within the host. Besides acylhomoserine lactone (AHL) mediated las and rhl systems, this organism possesses Pseudomonas quinolone signalling (PQS) system based on alkyl quinolone signal molecules. The quinolone system represents another layer of sophistication in the complex quorum sensing cascade. Therefore, in the present study, we evaluated the contribution of the PQS system in the establishment of acute urinary tract infection (UTI) in the mouse model. For this, wild-type parent strain of P. aeruginosa MPAO1 and its isogenic single transposon mutant strains pqsH and pqsA were employed to induce UTI in mice. PQS molecules in the tissue homogenates of mice were detected by high performance thin layer chromatography (HP-TLC) method. Virulence of strains was assessed in terms of bacteriological count, histopathological lesions in the renal and bladder tissue and generation of pathological index markers like reactive nitrogen intermediates and malondialdehyde. HP-TLC analysis showed presence of PQS molecules in the renal and bladder tissue of mice infected with MPAO1 while no PQS was detected in case of pqsH and pqsA mutant strains. Results indicated that MPAO1 possessing fully functional PQS biosynthetic genes was highly virulent and caused acute pyelonephritis with severe inflammation and tissue destruction. On the contrary, significant reduction in the log count, mild tissue damage and declined levels of pathological markers were observed in mice infected with mutant strains as compared to MPAO1. Further among mutants, all these parameters were maximally impaired in the pqsA mutant in which synthesis of alkyl quinolones was completely abolished due to the transposon mutation in respective gene. Virulence of the pqsH mutant strain was lesser than that of the MPAO1 but higher than pqsA mutant. In addition, the levels of locally generated pro- and anti-inflammatory cytokines were also found to be low in the renal homogenates of mice infected with the mutant strains. Further, supplementation of strains with PQS resulted in significant enhancement in the virulence as indicated by increased bacterial load, severe histopathological damage and enhanced levels of pro-inflammatory cytokines. These findings provide a new insight into the relevant importance of the Pseudomonas quinolone signalling system in the acute UTI caused by P. aeruginosa. This system can be a potential target for futuristic anti-infective approach against this organism.

Acute kidney injury: what part do toll-like receptors play?

The innate immune system plays an important role as a first response to tissue injury. This first response is carried out via germline-encoded receptors. Toll-like receptors (TLRs) are the first identified and best studied family of pattern recognition receptors. TLRs are expressed on a variety of cell types, including epithelial cells, endothelia, dendritic cells, monocytes/macrophages, and B- and T-cells. TLRs initiate innate immune responses and concurrently shape the subsequent adaptive immune response. They are sensors of both pathogens, through the exogenous pathogen-associated molecular patterns (PAMPs), and tissue injury, through the endogenous danger-associated molecular patterns (DAMPs). TLR signaling is critical in defending against invading microorganisms; however, sustained receptor activation is also implicated in the pathogenesis of inflammatory diseases. Ischemic kidney injury involves early TLR-driven immunopathology, and the resolution of inflammation is needed for rapid regeneration of injured tubule cells. Notably, the activation of TLRs also has been implicated in epithelial repair. This review focuses on the role of TLRs and their endogenous ligands within the inflammatory response of acute kidney injury.

TLR-4 polymorphisms and leukocyte TLR-4 expression in febrile UTI and renal scarring

BACKGROUND

In this study, we aimed to determine the relation of TLR-4 Asp299Gly and Thr399Ile polymorphisms and monocyte/neutrophil TLR-4 expression to febrile urinary tract infection (UTI) and renal scar development in children.

METHODS

The study was performed in children with a history of febrile UTI. Patients with and without renal scarring were classified as group 1 and group 2, respectively, while the control cases in our previous study were used as the control group (group 3). All three groups were compared for the rate of TLR-4 Asp299Gly and Thr399Ile polymorphisms, and for basal and lipopolysaccharide-stimulated monocyte/neutrophil TLR-4 expression levels.

RESULTS

There were 168 patients (86 in group 1, 82 in group 2) and 120 control cases. Monocyte/neutrophil TLR-4 expression levels were similar in groups 1 and 2. However, both groups had lower TLR-4 expression than group 3. The rate of TLR-4 Asp299Gly polymorphism was not different in all groups. TLR-4 Thr399Ile polymorphism was higher in groups 1 and 2 than in group 3 (14.0, 12.2, and 2.0 %, respectively), while group 1 and group 2 were not different. Furthermore, monocyte TLR-4 expression level was lower in those having TLR-4 Thr399Ile polymorphism than in those without this polymorphism.

CONCLUSIONS

Patients with febrile UTI had more frequent TLR-4 Thr399Ile polymorphism and lower monocyte/neutrophil TLR-4 expression. These findings indicate that children carrying TLR-4 Thr399Ile polymorphism and/or having low level of monocyte/neutrophil TLR-4 expression have a tendency to develop febrile UTI. However, we could not show the association of TLR-4 polymorphisms and of TLR-4 expression level to renal scarring.

Expression of IL-23, VEGF and TLR2/TLR4 on mononuclear cells after exposure to Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative, aerobic bacillus causing infections of the respiratory and other organ systems in susceptible hosts. Although it does not cause pulmonary infections in immunocompetent individuals, P. aeruginosa causes chronic lung infection in individuals with cystic fibrosis and nosocomial pneumonia resulting in significant morbidity and mortality. Exogenous administration of an important P. aeruginosa virulence factor, lipase, present in P. aeruginosa culture supernatant, induces potent mononuclear cell activation leading to the production of numerous proinflammatory cytokines. In particular, P. aeruginosa culture supernatant stimulated increased proliferation of THP-1 cells and monocytes (MN). The addition of culture supernatant to THP-1 cells and MN also induced Interleukin (IL)-23 and vascular endothelial growth factor (VEGF) release in a time-dependent manner. To investigate whether any compounds present in the supernatant lipase contributed to releasing IL-23 and VEGF, the culture supernatant from P. aeruginosa containing lipase was treated with hexadecylsulfonylfluoride (AMSF). The AMSF-treated culture supernatant (CS) did not show any induction on the IL-23 and VEGF release compared to the cells treated with CS without AMSF. We also showed that Toll-like receptors (TLR)2/TLR4 are expressed in THP-1 cells and MN treated with P. aeruginosa CS in a time-dependent fashion. Flow cytometry analysis revealed a higher TLR4 and a lower TLR2 expression at 48 and 72 h of treatment. The treatment of cells with TLR4 neutralizing antibody, and to a lesser extent with TLR2 neutralizing antibody, resulted in a decrease in P. aeruginosa CS-induced IL-23 and VEGF production.

Assessment of Toll-like receptor-4 gene polymorphism on pyelonephritis and renal scar

The aim of this study was to evaluate the effect of the TLR-4 gene TLR4 c.896A < G polymorphism on the development and clinical severity of urinary tract infections (UTI) and renal scar formations in children. The patients with first diagnosis of UTI (n = 112) and healthy controls (n = 93) were enrolled in the study. The TLR4 c.896A < G polymorphism was analysed in groups. The mean age of the patients in the study group was 8.1 ± 3.5 years and 9.2 ± 2.7 years for those in the control group. The TLR4 c.896A < G polymorphism was detected in 12.5% in the UTI group and in 15.1% of the control group. Forty patients showed pyelonephritis (PN) with scar tissue, 37 patients had PN without scars, and 35 patients had lower UTI. The TLR4 c.896A < G polymorphism was found in 22.5% of patients with scar-positive PN, and it was also present in 10.8% of patients with scar-negative PN and 2.9% of patients with lower UTI. We found higher TLR4 c.896A < G polymorphism and allelic frequency in patients with upper UTI compared to patients with lower UTI (P = 0.041 and P = 0.039, respectively). No significant difference was observed between patients and the control group for TLR-4 c.896A3. The TLR4 c.896A < G polymorphism and alleles were higher in patients with upper UTI than in patients with lower UTI. The TLR4 c.896A < G polymorphism frequency was nearly twice that in the scar-positive PN patients when compared to the scar-negative patients. Larger-scale studies involving larger numbers of patients should be performed.

How does the urothelium affect bladder function in health and disease? ICI-RS 2011

The urothelium is a multifunctional tissue that not only acts as a barrier between the vesical contents of the lower urinary tract and the underlying tissues but also acts as a sensory organ by transducing physical and chemical stresses to the attendant afferent nervous system and underlying smooth muscle. This review will consider the nature of the stresses that the urothelium can transduce; the transmitters that mediate the transduction process; and how lower urinary pathologies, including overactive bladder syndrome, painful bladder syndrome and bacterial infections, are associated with alterations to this sensory system. In particular, the role of muscarinic receptors and the TRPV channels system will be discussed in this context. The urothelium also influences the contractile state of detrusor smooth muscle, both through modifying its contractility and the extent of spontaneous activity; potential pathways are discussed. The potential role that the urothelium may play in bladder underactivity is introduced, as well as potential biomarkers for the condition that may cross the urothelium to the urine. Finally, consideration is given to vesical administration of therapeutic agents that influence urinary tract function and how the properties of the urothelium may determine the effectiveness of this mode of delivery.

LY96, UPKIB mutations and TLR4, CD14, MBL polymorphisms in children with urinary tract infection

OBJECTIVE

To evaluate genetic variations of innate immune system such as mannose binding lectin (MBL), Toll like receptor 4 (TLR4), CD14, LY96 (MD2) and Uroplakin 1B (UPK1B) genes in children with recurrent urinary tract infection (UTI).

METHODS

The study included 30 children with recurrent UTI and 30 healthy controls. Blood was drawn and analysed for genetic polymorphisms of MBL, TLR4 and CD14 genes by the PCR-RFLP method. Direct DNA sequencing analysis was performed for LY96 and UPK 1B gene mutation in 10 children from UTI group and 5 children from control group.

RESULTS

TLR4 gene Thr399Ile polymorphism was not observed in any child. Genotype distribution and allele frequency of Asp299Gly polymorphism was similar in both groups (p = 0.55). Codon 54 polymorphism of the MBL gene was similar in UTI and control groups (p = 0.49). -159 CC/CT/TT genotypes of CD14 gene was similar between the two groups (p = 0.14). UPK1B and LY96 gene DNA sequence analysis was similar in UTI and control groups.

CONCLUSIONS

This study is the first study in which different parts of the innate immune system were evaluated in UTI etiopathogenesis in Turkish children. The results did not point out a significant role of any of the genes evaluated in this study.

Acute pyelonephritis and renal scarring are caused by dysfunctional innate immunity in mCxcr2 heterozygous mice

The CXCR1 receptor and chemokine CXCL8 (IL-8) support neutrophil-dependent clearance of uropathogenic Escherichia coli from the urinary tract. CXCR1 is reduced in children prone to pyelonephritis, and heterozygous hCXCR1 polymorphisms are more common in this patient group than in healthy individuals, strongly suggesting a disease association. Since murine CXCR2 (mCXCR2) is functionally similar to human CXCR1, we determined effects of gene heterozygosity on the susceptibility to urinary tract infection by infecting heterozygous (mCxcr2(+/-)) mice with uropathogenic Escherichia coli. Clearance of infection and tissue damage were assessed as a function of innate immunity in comparison to that in knockout (mCxcr2(-/-)) and wild-type (mCxcr2(+/+)) mice. Acute sepsis-associated mortality was increased and bacterial clearance drastically impaired in heterozygous compared to wild-type mice. Chemokine and neutrophil responses were delayed along with evidence of neutrophil retention and unresolved kidney inflammation 1 month after infection. This was accompanied by epithelial proliferation and subepithelial fibrosis. The heterozygous phenotype was intermediate, between knockout and wild-type mice, but specific immune cell infiltrates that accompany chronic infection in knockout mice were not found. Hence, the known heterozygous CXCR1 polymorphisms may predispose patients to acute pyelonephritis and urosepsis.

Evaluation of tumour necrosis factor-alpha and interleukin-1beta in an experimental pyelonephritis model induced with planktonic and biofilms cells of Pseudomonas aeruginosa

Urinary tract infections may induce severe inflammation, transient impairment in renal function and scar formation, ranging in severity from acute symptomatic pyelonephritis to chronic pyelonephritis, and have the potential to lead to renal failure and death. In the present study, the relationship between production of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), neutrophil recruitment, bacterial colonization and tissue damage was investigated using a mouse model of acute ascending pyelonephritis induced with planktonic and biofilm cells of Pseudomonas aeruginosa. Neutrophil influx correlated with rise in TNF-alpha and IL-1beta, indicating an association between these cytokines and neutrophil infiltration. However, biofilm cells of P aeruginosa induced higher levels of TNF-alpha and IL-1beta leading to higher neutrophil infiltration causing tissue damage, assessed in terms of malondialdehyde, lactate dehydrogenase and glutathione content, which may have contributed to bacterial persistence compared with their planktonic counterparts. The results of the present investigation suggest that exaggerated cytokine production during P aeruginosa-induced pyelonephritis causes tissue damage operative through neutrophil recruitment leading to bacterial persistence in host tissues. The findings of the present study may be relevant for the better understanding of disease pathophysiology and for the future developments of preventive strategies against pyelonephritis based on anti-inflammatory intervention.

Toll-like receptor 2 mediates inhibition of HCO(3)(-) absorption by bacterial lipoprotein in medullary thick ascending limb

Bacterial infection and sepsis are associated with renal tubule dysfunction and dysregulation of systemic electrolyte balance but the underlying mechanisms are incompletely understood. Recently, we demonstrated that HCO(3)(-) absorption by the medullary thick ascending limb (MTAL) is inhibited by gram-negative bacterial LPS through activation of Toll-like receptor 4 (TLR4). Here, we examined whether MTAL transport is altered by activation of TLR2, the receptor predominantly responsible for recognizing gram-positive bacteria. Confocal immunofluorescence showed expression of TLR2 in the basolateral membrane domain of rat and mouse MTALs. The functional role of TLR2 was examined in perfused MTALs using Pam(3)CSK(4), a bacterial lipoprotein analog that specifically activates TLR2. Adding Pam(3)CSK(4) to the bath decreased HCO(3)(-) absorption by 25%. The inhibition by Pam(3)CSK(4) was eliminated in MTALs from TLR2(-/-) mice. HCO(3)(-) absorption was also inhibited by the TLR2 agonists lipoteichoic acid and peptidoglycan, two cell wall components of gram-positive bacteria. The MEK/ERK inhibitor U0126 eliminated inhibition of HCO(3)(-) absorption by bath LPS but had no effect on inhibition by Pam(3)CSK(4). The inhibition by Pam(3)CSK(4) was eliminated by the protein kinase C inhibitors chelerythrine Cl and bisindolylmaleimide. Moreover, the inhibition by Pam(3)CSK(4), lipoteichoic acid, and peptidoglycan was additive to inhibition by LPS. Thus, agonists of basolateral TLR2 and TLR4 inhibit HCO(3)(-) absorption independently through distinct signaling pathways. We conclude that bacterial components act directly through TLRs to modify the transport function of renal tubules. During polymicrobial sepsis, gram-positive bacterial molecules acting through TLR2 and gram-negative LPS acting through TLR4 can function through parallel signaling pathways to impair MTAL transport. The inhibition of luminal acidification may impair the ability of the kidneys to correct systemic acidosis that contributes to sepsis pathogenesis.

Update on childhood urinary tract infection and vesicoureteral reflux

Urinary tract infection (UTI) is a leading cause of serious bacterial infection in young children. Vesicoureteral reflux (VUR), a common pediatric urologic disorder, is believed to predispose to UTI, and both are associated with renal scarring. The complex interaction of bacterial virulence factors and host defense mechanisms influence renal damage. However, some renal parenchymal abnormalities associated with VUR are noninfectious in origin. Long-term, renal parenchymal injury may be associated with hypertension, pregnancy complications, proteinuria, and renal insufficiency. Optimal management of VUR and UTI is controversial because of the paucity of appropriate randomized controlled trials; there is a need for well-designed studies. The recently launched Randomized Intervention for children with VesicoUreteral Reflux (RIVUR) study hopefully will provide insight into the role of antimicrobial prophylaxis of UTI in children with VUR.

Lipopolysaccharide directly alters renal tubule transport through distinct TLR4-dependent pathways in basolateral and apical membranes

Bacterial infection of the kidney is associated with renal tubule dysfunction and dysregulation of systemic electrolyte balance. Whether bacterial molecules directly affect renal tubule transport is unknown. We examined the effects of LPS on HCO3(-) absorption in the isolated rat and mouse medullary thick ascending limb (MTAL). LPS decreased HCO3(-) absorption when added to bath or lumen. The MEK/ERK inhibitor U0126 eliminated inhibition by bath LPS but had no effect on inhibition by lumen LPS. Conversely, the mammalian target of rapamycin (mTOR) inhibitor rapamycin eliminated inhibition by lumen LPS but had no effect on inhibition by bath LPS. Inhibiting basolateral Na(+)/H(+) exchange with amiloride eliminated inhibition of HCO3(-) absorption by lumen but not bath LPS. Confocal immunofluorescence showed expression of TLR4 in basolateral and apical membrane domains. Inhibition of HCO3(-) absorption by bath and lumen LPS was eliminated in MTALs from TLR4(-/-) mice. Thus LPS inhibits HCO3(-) absorption through distinct TLR4-dependent pathways in basolateral and apical membranes. These results establish that bacterial molecules can directly impair the transport function of renal tubules, identifying a new mechanism contributing to tubule dysfunction during bacterial infection. The LPS-induced reduction in luminal acidification may contribute to Gram-negative pathogenicity by promoting bacterial adherence and growth and impairing correction of infection-induced systemic acid-base disorders.

The innate immune response in ischemic acute kidney injury

Kidney ischemia reperfusion injury is a major cause of morbidity in both allograft and native kidneys. Ischemia reperfusion-induced acute kidney injury is characterized by early, alloantigen-independent inflammation. Major components of the innate immune system are activated and participate in the pathogenesis of acute kidney injury, plus prime the allograft kidney for rejection. Soluble members of innate immunity implicated in acute kidney injury include the complement system, cytokines, and chemokines. Toll-like receptors (TLRs) are also important contributors. Effector cells that participate in acute kidney injury include the classic innate immune cells, neutrophils and macrophages. Recent data has unexpectedly identified lymphocytes as participants of early acute kidney injury responses. In this review, we will focus on immune mediators that participate in the pathogenesis of ischemic acute kidney injury.

Pathways of renal injury in systemic gram-negative sepsis

Acute renal failure is a grave complication of systemic gram-negative sepsis. The pathophysiological mechanisms of sepsis leading to kidney injury result in part from systemic inflammatory and haemodynamic alterations. These are triggered by the interaction of endotoxin with Toll-like receptor 4 (TLR4) on cells of the immune system. Recently, TLR4 and other co-effector molecules were identified on renal tubular and vascular cells. Furthermore, it was demonstrated that systemic endotoxin has direct access to renal sites where these receptors are expressed. Therefore, we review data in support of this novel pathway of renal injury in sepsis, whereby systemic endotoxin causes direct injury through interactions with local epithelial and endothelial TLR4.

The nuclear factor kappa-B pathway in airway epithelium regulates neutrophil recruitment and host defence following Pseudomonas aeruginosa infection

Pseudomonas aeruginosa pneumonia usually results from a deficit of the innate immune system. To investigate whether inflammatory signalling by airway epithelial cells provides a pivotal line of defence against P. aeruginosa infection, we utilized two separate lines of inducible transgenic mice that express a constitutive activator of the nuclear factor kappa-B (NF-kappaB) pathway (IKTA) or a dominant inhibitor of NF-kappaB (DNTA) in airway epithelial cells. Compared with control mice, IKTA mice showed an enhanced host response to P. aeruginosa infection with greater neutrophil influx into the lungs, increased expression of Glu-Leu-Arg-positive (ELR(+)) CXC chemokines macrophage inflammatory protein-2 and keratinocyte chemoattractant (KC), superior bacterial clearance and improved survival at 24 h after infection. Neutrophil depletion abrogated the improvement in host defence identified in IKTA mice. In contrast, DNTA mice showed impaired responses to P. aeruginosa infection with higher bacterial colony counts in the lungs, decreased neutrophilic lung inflammation and lower levels of KC in lung lavage fluid. DNTA mice given recombinant KC at the time of P. aeruginosa infection demonstrated improved neutrophil recruitment to the lungs and enhanced bacterial clearance. Our data indicate that the NF-kappaB pathway in airway epithelial cells plays an essential role in defence against P. aeruginosa through generation of CXC chemokines and recruitment of neutrophils.

Antimicrobial mechanisms of the urinary tract

The urinary tract is a key system to maintain the homeostasis of the human body. It is relatively open to the outside environment, the perineum, a region highly colonized by bacteria. Bacteria can even be found in urine of healthy individuals. Still, urinary tract infections are far less frequent than it could be expected under these conditions. The high resistance against such infections has been observed already more than 100 years ago. Since then, many antimicrobial mechanisms of the urinary tract have been elucidated. Some questions, however, remain challenges for patients, scientists and health care professionals. In this review, we try to summarize the achieved knowledge about mechanisms, maintaining the urinary tract free of infection. In addition, we discuss their relevance and possible clinical application.

The relative importance of local and systemic complement production in ischaemia, transplantation and other pathologies

Besides a critical role in innate host defence, complement activation contributes to inflammatory and immunological responses in a number of pathological conditions. Many tissues outside the liver (the primary source of complement) synthesise a variety of complement proteins, either constitutively or response to noxious stimuli. The significance of this local synthesis of complement has become clearer as a result of functional studies. It revealed that local production not only contributes to the systemic pool of complement but also influences local tissue injury and provides a link with the antigen-specific immune response. Extravascular production of complement seems particularly important at locations with poor access to circulating components and at sites of tissue stress responses, notably portals of entry of invasive microbes, such as interstitial spaces and renal tubular epithelial surfaces. Understanding the relative importance of local and systemic complement production at such locations could help to explain the differential involvement of complement in organ-specific pathology and inform the design of complement-based therapy. Here, we will describe the lessons we have learned over the last decade about the local synthesis of complement and its association with inflammatory and immunological diseases, placing emphasis on the role of local synthesis of complement in organ transplantation.

Heat shock protein 72 (HSPA1B) gene polymorphism and Toll-like receptor (TLR) 4 mutation are associated with increased risk of urinary tract infection in children

Innate immunity and urinary tract response play a central role in the development of urinary tract infection (UTI). Heat shock protein (HSP) 72 and Toll-like receptor (TLR) 4 are among the key elements of innate defence mechanisms. This study assesses the role of HSPA1B A(1267)G and TLR4 A(896)G polymorphisms using allele-specific polymerase chain reaction in 103 patients treated with recurrent UTI. Allelic prevalence was compared with reference values of 235 healthy controls. Clinical data were also statistically evaluated. TLR4 (896)AG genotype and TLR4 (896)G allele had also higher prevalence in UTI patients versus controls (p = 0.031 and 0.041, respectively). Our data indicates a relationship between the carrier status of HSPA1B (1267)G and TLR4 (896)G alleles and the development of recurrent UTI in childhood independently of other renal abnormalities, while raising further questions about the clinical and therapeutic relevance of these polymorphisms in everyday pediatric nephrology.

Urothelial CD44 FacilitatesEscherichia coliInfection of the Murine Urinary Tract

Escherichia coli is the most common pathogen found in urinary tract infections (UTIs), mainly affecting children and women. We report that CD44, a hyaluronic acid (HA) binding protein that mediates cell-cell and cell-matrix interactions, facilitates the interaction of E. coli with urothelial cells and thus the infection of the host. We found that CD44 is constitutively expressed on urothelial cells and that HA accumulates in E. coli-induced UTI. In CD44-deficient mice, the bacterial outgrowth was dramatically less compared with wild-type mice despite similar granulocyte influx in the bladder and in the kidney as well as comparable cytokines/chemokines levels in both genotypes. E. coli was able to bind HA, which adhered to CD44-positive tubular epithelial cells. Most importantly, the interaction of CD44 on tubular epithelial cells with HA facilitated the migration of E. coli through the epithelial monolayer. The results provide evidence that CD44 on urothelial cells facilitates E. coli UTI. Disruption of the interaction between CD44 and HA in the bladder may provide a new approach to prevent and to treat UTI.

Triggers of inflammation after renal ischemia/reperfusion

Renal ischemia/reperfusion (I/R) is a common cause of acute renal failure (ARF). Ischemic ARF is associated with tubulointerstitial inflammation, and studies using animal models have demonstrated that the inflammatory response to I/R exacerbates the resultant renal injury. Ischemic ARF involves complement activation, the generation of cytokines and chemokines within the kidney, and infiltration of the kidney by leukocytes. Recent work has revealed some of the events and signals that trigger the inflammatory response to aseptic, hypoxic injury of the kidney. In many ways, the inflammatory reaction to this injury resembles that seen during ascending urinary infection, and it may represent a general response of the tubular epithelial cells (TECs) to stress or injury. A greater understanding of the signals that trigger the inflammatory response may permit the development of effective therapies to ameliorate ischemic ARF.

Renal Toll-like receptors: recent advances and implications for disease

Toll-like receptors (TLRs) are proteins that recognize specific molecular patterns of pathogens. They can also interact with a variety of endogenous ligands. When stimulated, TLRs initiate a cascade of signaling events leading to the production of a myriad of cytokines and effector molecules. Early investigations extensively characterized TLRs on cells of the innate immune system. More recently, TLRs have been found to reside in organs such as the heart, lungs, intestines, liver and kidneys. The role of these TLRs is not fully understood and is the subject of intensive current research. The available information indicates that renal TLRs have the potential to interact with exogenous and endogenous ligands, thereby influencing kidney function in health and disease. Here, we present an overview of what is currently known about renal TLRs, and discuss the potential implications for further research and clinical practice.

Sepsis induces changes in the expression and distribution of Toll-like receptor 4 in the rat kidney

Toll-like receptors (TLRs) are now recognized as the major receptors for microbial pathogens on cells of the innate immune system. Recently, TLRs were also identified in many organs including the kidney. However, the cellular distribution and role of these renal TLRs remain largely unknown. In this paper, we investigated the expression of TLR4 in a cecal ligation and puncture (CLP) model of sepsis in Sprague-Dawley rats utilizing fluorescence microscopy. In sham animals, TLR4 was expressed predominantly in Tamm-Horsfall protein (THP)-positive tubules. In CLP animals, TLR4 expression increased markedly in all tubules (proximal and distal), glomeruli, and the renal vasculature. The staining showed a strong apical distribution in all tubules. A moderately less intense cellular signal colocalized partially with the Golgi apparatus. In addition, kidneys from septic rats showed increased expression of CD14 and THP. They each colocalized strongly with TLR4, albeit in different tubular segments. We also imaged the kidneys of live septic animals with two-photon microscopy after fluorescent lipopolysaccharide (LPS) injection. Within 10 min, LPS was seen at the brush border of some proximal tubules. Within 60 min, LPS was fully cytoplasmic in proximal tubules. Conversely, distal tubules showed no LPS uptake. We conclude that TLR4, CD14, and THP have specific renal cellular and tubular expression patterns that are markedly affected by sepsis. Systemic endotoxin can freely access the tubular and cellular sites where these proteins are present. Therefore, locally expressed TLRs and other interacting proteins could potentially modulate the renal response to systemic sepsis.

Upregulation of chemokine CXCL1/KC by leptospiral membrane lipoprotein preparation in renal tubule epithelial cells

We have previously shown that leptospiral membrane lipoprotein preparation (LMLP) extracted from pathogenic Leptospira santarosai serovar Shermani stimulates the secretion of pro-inflammatory mediators in renal tubule epithelial cells, and implicated its role in the initiation of tubulointerstitial nephritis. Renal tubulointerstitial injury is characterized by inflammatory cell infiltrate; however, the stimuli for leukocyte recruitment are not fully understood. Initial studies by cytokine protein array analysis revealed significant upregulation of neutrophil-chemoattractant keratinocyte-derived chemokine (CXCL1/KC) at nanogram range of LMLP stimulation in cultured murine proximal tubule cells (PTCs). As PTCs express Toll-like receptors (TLRs), this study investigated the roles of TLR signaling pathways in PTCs stimulated by LMLP and its relation to CXCL1/KC secretion. The LMLP stimulated the early secretion of CXCL1/KC and enhanced the level of TLR2 mRNA expression in PTCs through time- and dose-dependent effect. The LMLP-stimulated secretion of human growth-related oncogene alpha, a functional homolog to murine KC, in TLR-defective human embryonic kidney 293 cells transiently transfected with TLR2-expressing plasmids and the response was augmented by coexpression of TLR1 and TLR2. Moreover, silencing of TLR2, myeloid differentiation factor 88, and TNF receptor-associated factor 6 with specific small interfering RNA significantly reduces the response caused by LMLP in PTCs. The LMLP-stimulated CXCL1/KC secretion was also significantly reduced by pre-incubating PTCs with a specific p38 inhibitor. These results indicate that LMLP stimulates the production of CXCL1/KC to recruit polymorphonuclear neutrophils at the site of inflammation through a TLR2-mediated pathway in renal tubule cells.

Pathogenesis of urinary tract infection: an update

PURPOSE OF REVIEW

Urinary tract infection is the second most common bacterial infection in children. It may cause renal scarring leading to secondary hypertension and chronic kidney disease. Recent information has greatly improved our understanding of the pathogenesis of urinary tract infection and renal scarring.

RECENT FINDINGS

Urothelium, an anatomical barrier for innate immune responses, expresses toll-like receptors with the capacity to recognize pathogen-associated molecular patterns. Engagement of toll-like receptors can lead to uroepithelial cell activation and production of inflammatory mediators. These include complement proteins, other bactericidal peptides, cytokines, chemokines, defensins and adhesion molecules. The resulting inflammatory infiltrate serves to aid bacterial clearance but can also lead to renal damage. Furthermore, interactions between urinary proteins, such as Tamm-Horsfall protein, and TLR-4 add to the complexity of this defense system. Interindividual variability in cellular response may in part be responsible for variable clinical outcomes. Polymorphisms in a number of candidate genes in this host defense mechanism may be involved in determining those patients who are susceptible to recurrent infections and renal scarring following urinary tract infection.

SUMMARY

Further understanding of the basic molecular mechanisms of urinary tract infection and translating these bench data to the bedside holds the promise of improving diagnosis and therapeutic strategies of treating urinary tract infection and preventing recurrence and renal scarring.

[Treatment and prophylaxis of recurrent urinary tract infections]

Recurrent urinary tract infections are typical diseases of sexually active young women. Only elder women show significant rates of underlying, mostly urological diseases. Besides behavioral changes long-term antimicrobial therapy is still the mainstay of both prophylaxis and therapy. This report provides information on the etiology for recurrent urinary tract infections. Strategies for prevention are illustrated. The actual significances of organic remedies and antibiotics respectively are discussed; ineffective therapies are identified. Furthermore an outlook is given on promising novel therapeutics, i.e. vaccines which are already tested in clinical trials.

Chemokine response to febrile urinary tract infection

BACKGROUND

Mucosal CXC chemokines recruit inflammatory cells to the infected urinary tract. The chemokine response repertoire of the urinary tract and the relationship to disease severity have not been examined, however.

METHODS

This study quantified CXC (CXCL1, CXCL3, CXCL5, CXCL8, CXCL9, and CXCL10) and CC (CCL2, CCL4, and CCL5) chemokines in sequential urine samples obtained from 50 patients with febrile urinary tract infections during 24 hours after diagnosis.

RESULTS

All patients had elevated chemokine levels, but bacteremic infections caused higher CXCL1, CXCL3, CXCL5, CXCL8, and CCL2 responses. CCL2 and CXCL8 levels were higher in patients with acute pyelonephritis symptoms and CCL2, CXCL3, CCL4, CXCL5, and CXCL10 were significantly correlated to C-reactive protein (CRP) and temperature. Women and men showed different chemokine responses.

CONCLUSION

Febrile urinary tract infections are accompanied by a complex chemokine response. The response magnitude reflects disease severity, and the repertoire is influenced by gender and underlying disease.

Toll-like receptor 2-mediated expression of beta-defensin-2 in human corneal epithelial cells

We previously showed that human corneal epithelial cells (HCECs) express Toll-like receptors (TLRs), which recognize gram-positive bacteria and respond to Staphylococcus aureus infection by the expression and secretion of proinflammatory cytokines and beta-defensin-2 (hBD2). In this study, we further elucidated the underlying mechanisms regulating hBD-2 expression and its role in innate defense in HCECs in response to S. aureus challenge. Exposure of HUCL cells, a telomerase-immortalized HCEC line, to S. aureus, its exoproducts (1:10 dilution), or synthetic lipopeptide Pam3Cys (10 microg/ml) resulted in the up-regulation of hBD-2, but not hBD1 and hBD3. Similar to HUCL cells, primary HCECs responded to S. aureus-exoproducts and Pam3Cys challenge by expressing hBD2 mRNA and secreting hBD2 into the culture media. Furthermore, these stimuli induced the expression of TLR2 at both mRNA and protein levels. Consistently with its role as a major pattern-recognizing receptor, TLR2 was located at the cell surface by cell surface biotinylation. The treatment of HUCL cells with TLR2 neutralizing antibody resulted in a significant decrease in Pam3Cys-induced hBD2 production as well as IL-6, IL-8, and TNF-alpha secretion. The Pam3Cys-induced hBD2 expression was completely blocked by NF-kappaB inhibitors and partially inhibited by p38 MAP kinase and the JNK inhibitors. Conditioned media derived from HCECs challenged with S. aureus-exoproducts or Pam3Cys exhibited antibacterial activity against S. aureus, Pseudomonas aeruginosa and Escherichia coli. These findings suggest that S. aureus induces hBD2 production through TLR2-mediated pathways in HCECs and that pathogen-challenged, TLR-activated HCECs possess antimicrobial activity. Thus, the epithelium might play a role in innate defense against bacterial infection by directly killing bacteria in the cornea.