Local and systemic antibody responses accompany spontaneous resolution of experimental cystitis in cynomolgus monkeys

Bladder-draining lymph nodes support germinal center B cell responses during urinary tract infection in mice

Bacterial urinary tract infections (UTIs) are both common and exhibit high recurrence rates in women. UTI healthcare costs are increasing due to the rise of multidrug-resistant (MDR) bacteria, necessitating alternative approaches for infection control. Here, we directly observed host adaptive immune responses in acute UTI. We employed a mouse model in which wild-type C57BL/6J mice were transurethrally inoculated with a clinically relevant MDR UTI strain of uropathogenic Escherichia coli (UPEC). Firstly, we noted that rag1-/- C57BL/6J mice harbored larger bacterial burdens than wild-type counterparts, consistent with a role for adaptive immunity in UTI control. Consistent with this, UTI triggered in the bladders of wild-type mice early increases of myeloid cells, including CD11chi conventional dendritic cells, suggesting possible involvement of these professional antigen-presenting cells. Importantly, germinal center B cell responses developed by 4 weeks post-infection in bladder-draining lymph nodes of wild-type mice and, although modest in magnitude and transient in nature, could not be boosted with a second UTI. Thus, our data reveal for the first time in a mouse model that UPEC UTI induces local B cell immune responses in bladder-draining lymph nodes, which could potentially serve to control infection.

The clinical implications of bacterial pathogenesis and mucosal immunity in chronic urinary tract infection

Urinary tract infections (UTIs) exert a significant health and economic cost globally. Approximately one in four people with a previous history of UTI continue to develop recurrent or chronic infections. Research on UTI has primarily concentrated on pathogen behavior, with the focus gradually shifting to encompass the host immune response. However, these are centered on mouse models of Escherichia coli infection, which may not fully recapitulate the infective etiology and immune responses seen in humans. The emerging field of the urobiome also inadvertently confounds the discrimination of true UTI-causing pathogens from commensals. This review aims to present a novel perspective on chronic UTI by linking microbiology with immunology, which is commonly divergent in this field of research. It also describes the challenges in understanding chronic UTI pathogenesis and the human bladder immune response, largely conjectured from murine studies. Lastly, it outlines the shortcomings of current diagnostic methods in identifying individuals with chronic UTI and consequently treating them, potentially aggravating their disease due to mismanagement of prior episodes. This discourse highlights the need to consider these knowledge gaps and encourages more relevant studies of UTIs in humans.

A sublingual nanofiber vaccine to prevent urinary tract infections

Urinary tract infections (UTIs) are a major public health problem affecting millions of individuals each year. Recurrent UTIs are managed by long-term antibiotic use, making the alarming rise of antibiotic resistance a substantial threat to future UTI treatment. Extended antibiotic regimens may also have adverse effects on the microbiome. Here, we report the use of a supramolecular vaccine to provide long-term protection against uropathogenic Escherichia coli, which cause 80% of uncomplicated UTIs. We designed mucus-penetrating peptide-polymer nanofibers to enable sublingual (under the tongue) vaccine delivery and elicit antibody responses systemically and in the urogenital tract. In a mouse model of UTI, we demonstrate equivalent efficacy to high-dose oral antibiotics but with significantly less perturbation of the gut microbiome. We also formulate our vaccine as a rapid-dissolving sublingual tablet that raises response in mice and rabbits. Our approach represents a promising alternative to antibiotics for the treatment and prevention of UTIs.

Macrophages Subvert Adaptive Immunity to Urinary Tract Infection

Urinary tract infection (UTI) is one of the most common bacterial infections with frequent recurrence being a major medical challenge. Development of effective therapies has been impeded by the lack of knowledge of events leading to adaptive immunity. Here, we establish conclusive evidence that an adaptive immune response is generated during UTI, yet this response does not establish sterilizing immunity. To investigate the underlying deficiency, we delineated the naïve bladder immune cell compartment, identifying resident macrophages as the most populous immune cell. To evaluate their impact on the establishment of adaptive immune responses following infection, we measured bacterial clearance in mice depleted of either circulating monocytes, which give rise to macrophages, or bladder resident macrophages. Surprisingly, mice depleted of resident macrophages, prior to primary infection, exhibited a nearly 2-log reduction in bacterial burden following secondary challenge compared to untreated animals. This increased bacterial clearance, in the context of a challenge infection, was dependent on lymphocytes. Macrophages were the predominant antigen presenting cell to acquire bacteria post-infection and in their absence, bacterial uptake by dendritic cells was increased almost 2-fold. These data suggest that bacterial uptake by tissue macrophages impedes development of adaptive immune responses during UTI, revealing a novel target for enhancing host responses to bacterial infection of the bladder.

Urinary tract infection is a common infection with a high propensity for recurrence. The majority of infections are caused by uropathogenic E. coli, a growing public health concern with increasing prevalence of antibiotic resistant strains. Finding therapeutic options that circumvent the need for antibiotics, while boosting patients’ immune response to infection is desirable to counteract further increases in antibiotic resistance and to provide long-lasting resistance to infection. Currently, little is known about how adaptive immune responses, which typically prevent recurrent infection in other organs, arise from the bladder during urinary tract infection. Here, we investigated the initial interactions between immune cell populations of the bladder and uropathogenic E. coli, finding that macrophages are the principal cell population to engulf bacteria. Interestingly, these same cells appear to inhibit the development of adaptive immunity to the bacteria, as their depletion, prior to primary infection, results in a stronger immune response during bacterial challenge. We found that in the absence of macrophages, dendritic cells, which are the most potent initiators of adaptive immunity, are able to take up more bacteria for presentation. Our study has revealed a mechanism in which specific immune cells may act in a manner detrimental to host immunity.

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 innate immune response during urinary tract infection and pyelonephritis

Despite its proximity to the fecal flora, the urinary tract is considered sterile. The precise mechanisms by which the urinary tract maintains sterility are not well understood. Host immune responses are critically important in the antimicrobial defense of the urinary tract. During recent years, considerable advances have been made in our understanding of the mechanisms underlying immune homeostasis of the kidney and urinary tract. Dysfunctions in these immune mechanisms may result in acute disease, tissue destruction and overwhelming infection. The objective of this review is to provide an overview of the innate immune response in the urinary tract in response to microbial assault. In doing so, we focus on the role of antimicrobial peptides-a ubiquitous component of the innate immune response.

Establishment of a Mouse Model of Cystitis and Roles of Type 1 FimbriatedEscherichia coliin Its Pathogenesis

The role of type 1 fimbriae in promoting bladder colonization and the course of Escherichia coli cystitis were examined with type 1 fimbriated strains of clinically isolated E. coli. In the experiments of mice in vivo, intact bladder epithelium showed natural resistance to the adherence of type 1 fimbriated and non-fimbriated E. coli. However, the exfoliation of bladder superficial cells by trypsinization before the bacterial inoculation promoted the adhesion and colonization of type 1 fimbriated E. coli onto bladder epithelium. After colonization of E. coli, maximum numbers of E. coli and leukocytes were observed 3 days after inoculation. Nine days after inoculation, both of E. coli and leukocytes disappeared and the regeneration of superficial cells was observed. On the other hand, superficial cells in mice injected with phosphate-buffered saline or non-fimbriated E. coli regenerated 5 days after trypsinization. The present study demonstrated that the removal of superficial cells is essential for the adhesion and colonization of type 1 fimbriated E. coli onto bladder epithelium in vivo and a new model of E. coli cystitis in mice was established. The model which we established is valuable for histopathological, immunological, and therapeutic studies.

Waging war against uropathogenic Escherichia coli: winning back the urinary tract

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a substantial economic and societal burden-a formidable public health issue. Symptomatic UTI causes significant discomfort in infected patients, results in lost productivity, predisposes individuals to more serious infections, and usually necessitates antibiotic therapy. There is no licensed vaccine available for prevention of UTI in humans in the United States, likely due to the challenge of targeting a relatively heterogeneous group of pathogenic strains in a unique physiological niche. Despite significant advances in the understanding of UPEC biology, mechanistic details regarding the host response to UTI and full comprehension of genetic loci that influence susceptibility require additional work. Currently, there is an appreciation for the role of classic innate immune responses-from pattern receptor recognition to recruitment of phagocytic cells-that occur during UPEC-mediated UTI. There is, however, a clear disconnect regarding how factors involved in the innate immune response to UPEC stimulate acquired immunity that facilitates enhanced clearance upon reinfection. Unraveling the molecular details of this process is vital in the development of a successful vaccine for prevention of human UTI. Here, we survey the current understanding of host responses to UPEC-mediated UTI with an eye on molecular and cellular factors whose activity may be harnessed by a vaccine that stimulates lasting and sterilizing immunity.

Current concepts of molecular defence mechanisms operative during urinary tract infection

Mucosal tissues such as the gastrointestinal tract are typically exposed to a tremendous number of microorganisms and many of them are potentially dangerous to the host. In contrast, the urogenital tract is rather infrequently colonized with bacterial organisms and also devoid of physical barriers as a multi-layered mucus or ciliated epithelia, thereby necessitating separate host defence mechanisms. Recurrent urinary tract infection (UTI) represents the successful case of microbial host evasion and poses a major medical and economic health problem. During recent years considerable advances have been made in our understanding of the mechanisms underlying the immune homeostasis of the urogenital tract. Hence, the system of pathogen-recognition receptors including the Toll-like receptors (TLRs) is able to sense danger signalling and thus activate the host immune system of the genitourinary tract. Additionally, various soluble antimicrobial molecules including iron-sequestering proteins, defensins, cathelicidin and Tamm-Horsfall protein (THP), as well as their role for the prevention of UTI by modulating innate and adaptive immunity, have been more clearly defined. Furthermore, signalling mediators like cyclic adenosine monophosphate (cAMP) or the circulatory hormone vasopressin were shown to be involved in the defence of uropathogenic microbes and maintenance of mucosal integrity. Beyond this, specific receptors e.g. CD46 or beta1/beta 3-integrins, have been elucidated that are hijacked by uropathogenic E. coli to enable invasion and survival within the urogenital system paving the way for chronic forms of urinary tract infection. Collectively, the majority of these findings offer novel avenues for basic and translational research implying effective therapies against the diverse forms of acute and chronic UTI.

Local immune response to upper urinary tract infections in children

Vaccines are needed against urinary tract infections (UTIs) in children, as episodes of pyelonephritis (PN) may cause renal scarring. Local immune mechanisms are regarded to confer protection, yet they have been poorly characterized for children. This study explores the local immune response in children by looking for newly activated pathogen-specific antibody-secreting cells (ASC), expected to appear transiently in the circulation as a response to UTI. Urinary tract-originating ASC specific to each patient's own pathogen or P fimbria were studied in 37 children with PN. The children were examined for recidivism and renal scarring in a 6-month follow-up study. Pathogen-specific ASC were found in 33/37 children, with the magnitude increasing with age. In contrast to the case for adults, with immunoglobulin A (IgA) dominance, in 18/33 cases IgM dominated the response, and this occurred more frequently in infants (63%) than in older children (30%). The most vigorous response was found to whole Escherichia coli bacteria (geometric mean, 63 +/- 2,135 ASC/10(6) peripheral blood mononuclear cells [PBMC]), yet responses were found to P fimbriae (13 +/- 33 ASC/10(6) PBMC), too. The response peaked at 1 to 2 weeks and was low/negligible 3 to 7 weeks after the beginning of symptoms. Recidivism was seen in seven patients, and renal scarring was seen in nine patients. In conclusion, a response of circulating ASC was found in children with UTIs, with the magnitude increasing with age. Since IgM is not present in urine, the IgM dominance of the response suggests that systemic immune mechanisms are more important in the immune defense in children than in adults. In 81% of patients, no recidivism was seen, suggesting a successful immune defense.

Vaginal mucosal vaccine for recurrent urinary tract infections in women: results of a phase 2 clinical trial

PURPOSE

We assessed the clinical efficacy of vaginal mucosal immunization with a multivalent bacterial vaccine in women with recurrent urinary tract infections.

MATERIALS AND METHODS

A total of 75 patients in a double-blind study were randomly assigned to receive placebo only, primary immunization without boosters, or primary immunization plus boosters using vaginal suppositories containing placebo or vaccine. Vaccine suppositories contained 10 strains of heat-killed uropathogenic bacteria and placebo suppositories had no vaccine organisms. All women were monitored for 6 months to record the number of infections and adverse events.

RESULTS

Analysis of data on urinary tract infections caused by any bacteria showed the greatest difference in infection rates between patients in the vaccine plus boosters protocol compared to those receiving placebo only (p = 0.100). When only E. coli urinary tract infections were considered in the analysis, urinary tract infection recurrence rates were significantly less in women given booster immunizations compared to placebo (p = 0.0015). Furthermore, women who received vaccine with boosters and who were sexually active, less than 52 years old, or had not undergone hysterectomy had E. coli urinary tract infections at a much lower rate than women given placebo only (p = 0.0002, 0.002 and 0.003, respectively). No significant adverse events were associated with vaccine treatment.

CONCLUSIONS

This study demonstrated the efficacy of vaginal mucosal immunization with a multivalent vaccine in reducing recurrence of E. coli urinary tract infections. The results suggest that the vaccine may provide the most benefit to sexually active women in the 20 to 50-year-old age group.

Phase 2 clinical trial of a vaginal mucosal vaccine for urinary tract infections

PURPOSE

Recurrent urinary tract infections (UTIs) in susceptible women remain a common urological condition. With an increasing number of UTIs being caused by antibiotic resistant bacteria there is a need for alternatives to antibiotics. We determined whether multiple doses of a vaginal mucosal vaccine are effective for increasing long-term resistance to recurrent UTIs.

MATERIALS AND METHODS

A total of 54 women were entered into a double-blind, placebo controlled, phase 2 clinical trial using a vaginal vaccine containing 10 heat killed uropathogenic bacteria. Patients were withdrawn from prophylactic antibiotics and randomly assigned to 1 of 3 treatment groups, namely placebo only, primary immunization or primary plus booster immunizations. Subjects received treatments at 0, 1, 2, 6, 10 and 14 weeks. Placebo treated patients received suppositories without bacteria. The primary immunization group received vaccine suppositories, followed by 3 doses of placebo. Patients receiving booster immunizations were given 6 vaccine suppositories. All women were followed for 6 months to determine the time until first recurrence, number of infections and adverse reactions.

RESULTS

Women receiving 6 vaccine doses remained free of infections for a significantly longer period than those receiving placebo or primary immunizations. Of patients receiving 6 immunizations 55% did not experience an infection, whereas 89% of placebo treated women had UTIs. No women had significant adverse effects.

CONCLUSIONS

This study demonstrates that vaginal mucosal vaccine given for a 14-week period increased the time to re-infection in UTI susceptible women. The infrequent, minimal adverse reactions confirm previous observations on the safety of this vaginal mucosal immunization regimen.

Time course and host responses to Escherichia coli urinary tract infection in genetically distinct mouse strains

Recurrent urinary tract infections (UTIs) are a significant clinical problem for many women; however, host susceptibility factors have not been completely defined. The mouse model of induced UTI provides an experimental environment in which to identify specific host characteristics that are important in initial bacterial colonization of the urinary tract and in resolution of an infection. This study examined initial susceptibility, bacterial clearance, and host defense mechanisms during induction and resolution of Escherichia coli UTIs in genetically distinct strains of mice. Of the ten inbred strains tested, six (BALB/c, C3H/HeN, C57BL/6, DBA.1, DBA.2, and AKR) showed progressive resolution of bladder infections over a 14-day period. A constant, low-level bladder infection was observed in SWR and SJL mice. High bladder infection levels persisted over the 14-day study period in C3H/HeJ and C3H/OuJ mice. Kidney infection levels generally correlated with bladder infection levels, especially in C3H/HeJ and C3H/OuJ mice, the two most susceptible strains, in which infections became more severe with time after challenge. The degree of inflammation in bladder and kidneys, as well as antibody-forming cell responses, positively correlated with infection intensity in all strains except C3H/HeJ, which had minimal inflammation despite high infection levels. These results demonstrate two important aspects of host defense against UTI. First, the innate immune response to an infection in the bladder or kidneys consists primarily of local inflammation, which is followed by an adaptive response characterized in part by an antibody response to the infecting bacteria. Second, a UTI will be spontaneously resolved in most cases; however, in mice with specific genetic backgrounds, a UTI can persist for an extended length of time. The latter result strongly suggests that the presence or absence of specific host genes will determine how effectively an E. coli UTI will be resolved.

Induction of protective immunity after escherichia coli bladder infection in primates. Dependence of the globoside-specific P-fimbrial tip adhesin and its cognate receptor

Clinical observations suggest that immune mechanisms affect etiology and course of recurrent cystitis. A primate infection model was used to show that primary bladder infection with a uropathogenic P-fimbriated strain (binding to globoside present in the bladder wall) protects against rechallenge with homologous as well as heterologous Escherichia coli strains for up to 5-6 mo. In contrast, mutant derivatives producing P-fimbriae either lacking the tip adhesin protein or carrying an adhesin for which no bladder receptor was present, were unable to induce protection, even though they generated bladder infections of similar duration as the wild type. Therefore, the protective effect mediated by the adhesin seemed to depend upon the presence of its cognate receptor. Since the wild strain also mediated protection against mutants that lacked the adhesin, our data suggest that the globoside-binding PapG adhesin acts as an adjuvant during infection to enhance a specific response against other bacterial antigens. In fact, the globoside-binding strain DS17, but not the mutant DS17-1, unable to bind to membrane-bound globoside, elicited a secretory IgA response to LPS in urine. These in vivo findings suggest that bacterial adhesin-ligand interactions may have signaling functions of importance for the immune response.

Lipopolysaccharide-responder and nonresponder C3H mouse strains are equally susceptible to an induced Escherichia coli urinary tract infection

Host defense against bacterial urinary tract infections (UTI) includes both inflammatory and immune responses to infecting bacteria. The cellular events leading up to local inflammation are thought to be under genetic control and initiated by lipopolysaccharides (LPS) of gram-negative bacteria such as Escherichia coli. It has been previously reported that mice which lack functional Lps genes are more susceptible to induced E. coli UTI than mice with normal mitogenic responses to LPS. In contrast to these findings, data in this report demonstrate that LPS-responder and nonresponder C3H mouse strains are equally susceptible to E. coli UTI. When C3H/OuJ (Lps(n)/Lps(n)) and C3H/HeJ (Lps(d)/Lps(d)) were intravesically inoculated with equal numbers of uropathogenic E. coli organisms, neither strain was able to effectively resolve the induced UTI. The inability of C3H/OuJ mice to combat the infection was not due to an impaired response to LPS, nor could defect in the local inflammatory response be identified. The results indicate that factors other than LPS responsiveness are also important in determining hose resistance to UTI.

The protective role of enteral IgA supplementation in neonatal gut origin sepsis

Preterm infants and infants unable to breast feed are particularly susceptible to gut origin sepsis. Many studies have shown the benefits of breast milk in decreasing the incidence of bacterial infections in neonates. Little in vivo work has focused on prevention of neonatal gut origin sepsis with breast milk components. The aim of this study was to determine whether supplementation of a standard neonatal formula with exogenous, luminally administered, human secretory IgA protects against gut origin sepsis in a newborn rabbit model. Sixty New Zealand white rabbit pups were delivered by cesarean section 1 day preterm and divided into two groups--the IgA group (n = 26) and the non-IgA group (n = 34). Animals were gavage-fed a standard artificial formula (KMR) twice daily. The IgA group was supplemented on days 3 and 4 with 6.25 mg/kg of human secretory IgA. The non-IgA group received an equal volume of saline. On the evening of day 3, the animals were orally challenged with Escherichia coli K100. The quantity of bacteria that colonized the cecum was similar in the two groups. The quantity of bacteria that translocated to the mesenteric lymph node, liver, and spleen was significantly lower in the IgA group (P < .05). The incidence of translocation to the organs was also significantly lower in the IgA group (P < .05). The exogenous secretory IgA showed specificity to E coli K100 by ELISA. These data show that neonatal formula supplemented with human secretory IgA decreases the incidence and quantity of bacterial translocation of E coli K100 in a neonatal rabbit model.(ABSTRACT TRUNCATED AT 250 WORDS)

Resolution time of Escherichia coli cystitis is correlated with levels of preinfection antibody to the infecting Escherichia coli strain

OBJECTIVES

A number of studies in animals have demonstrated that immunization against uropathogenic bacteria can lessen the severity or duration of induced urinary tract infections (UTI). This study examined whether preinfection levels of serum or urinary anti-Escherichia coli antibodies were correlated with length of time needed to resolve an induced E coli cystitis.

METHODS

Serum and urine anti-E coli antibody levels in 36 control and 42 vaginally immunized cynomolgus monkeys were measured by enzyme-linked immunosorbent assay. Regression analyses were used to determine correlations between resolution time and preinfection antibody level, and to estimate antibody levels that might be associated with effective resolution of an E coli UTI.

RESULTS

Linear regression analysis showed significant correlations between short resolution time and high levels of serum immunoglobulin M (IgM), urinary secretory IgA, and urinary IgG specific for the infecting E coli strain. Serum IgM and urinary IgG anti-E coli levels in monkeys that cleared infections early were significantly higher than in animals with protracted infections. Logistic regression estimated the serum IgM and urinary IgG anti-E coli levels associated with a 50% probability of accelerated clearance to be 3.3 micrograms/mL and 2.7 micrograms/24 hours, respectively.

CONCLUSIONS

For this primate model, the observed correlations between short resolution time and pre-existing serum and urinary antibody suggest that antibody-mediated immunity is an important component of host defense against UTI.

Phase I clinical trial of vaginal mucosal immunization for recurrent urinary tract infection

In a phase I clinical trial to test safety and patient acceptance 25 women with a history of recurrent urinary tract infections but no identifiable anatomic abnormality received a multivalent vaccine instilled into the vagina. The vaccine contained 6 heat-killed Escherichia coli strains and 4 nonE. coli uropathogens. Only minimal adverse reactions were observed in the 5-month period following immunization. Total vaginal and urinary IgG and IgA increased significantly (p < 0.01 by repeated measures analysis of variance). Serum antibodies to some of the nonE. coli strains but not to the E. coli strains increased after vaginal immunization. While efficacy is yet to be shown, this study indicates that this vaginally applied urinary tract infection vaccine is well tolerated, and capable of increasing vaginal and urinary antibody.

Glycosaminoglycans and struvite calculi

Glycosaminoglycans (GAGs) are suspended in urine and are present on tissue surfaces in the urinary tract. Consequently, they have the potential to influence any pathological disorder in this environment, including urinary tract infections by Proteus mirabilis and struvite (NH4MgPO4.6H2(0)) urolithiasis. Although GAGs, suspended in urine, may inhibit the formation of other types of calculus minerals, no such effect has been reported in struvite calculi. Nevertheless, GAGs are a major component of the organic matrix of all types of urinary calculi. In contrast, there is evidence that the GAG layer on the bladder surface may act as a defence mechanism against infection by inhibiting bacterial adhesion. More studies are needed to elucidate fully the role of GAGs in urinary infections and struvite urolithiasis.

Vaginal immunization of monkeys against urinary tract infection with a multi-strain vaccine

Cynomolgus monkeys were treated with a vaccine containing 10 heat-killed uropathogenic bacteria including 6 Escherichia coli strains. The multi-strain vaccine was administered either as a vaginal surface immunogen or intramuscularly. Following an induced E. coli cystitis, bladder infections were significantly reduced compared with controls at 1 and 2 weeks (intramuscular route) or 1 week (vaginal route) after UTI. This vaccine has been shown to be efficacious against cystitis in humans when given parenterally and has now proved efficacious in nonhuman primates by the vaginal mucosal route.

Congenital immunodeficiencies in mice increase susceptibility to urinary tract infection

Severe combined immunodeficient (SCID), T cell deficient, and immunocompetent mice were challenged intravesically with viable uropathogenic Escherichia coli. In comparison to immunocompetent controls, SCID mice had significantly greater numbers of viable E. coli in their bladders and kidneys 7 days after inoculation. Splenic anti-E. coli antibody-forming cells (AFC) were virtually absent in SCID mice at 7.0 days after infection. Adoptive transfer of spleen cells from E. coli-immunized immunocompetent mice to SCID mice enhanced their resistance to urinary tract infection (UTI), as evidenced by lower bacterial counts in bladder and kidneys following an induced infection. Congenitally T cell deficient nude mice and immunocompetent heterozygous controls had equivalent bladder and kidney infection levels at 2 and 7 days after UTI. Immunocompetency thus appears to play a significant role in resistance to E. coli UTI in this animal model. Since mice deficient only in T cells did not show increased UTI susceptibility, T cell-independent antibody responses may be an important immunologic defense mechanism.

Attenuation of antibody response to acute pyelonephritis by treatment with antibiotics

While acute pyelonephritis is known to elicit an antibody response, it is also known that a patient who has had pyelonephritis once is susceptible to recurrent renal infection. Using our experimental model of pyelonephritis in the monkey, we tested whether antibiotic therapy of the acute disease would affect the antibody response. We found that it did, because antibiotic therapy beginning 72 h after bacterial inoculation attenuated the antibody response so that rechallenge 3 months later produced acute pyelonephritis and prolonged bacteriuria. The animals with untreated infection had an antibody response that lasted a sufficient period of time to prevent acute pyelonephritis after renal challenge. We have confirmed that antibody titers against P fimbriae are protective, and to a degree, this protective effect may be abrogated by antibiotic therapy.

Urinary tract infection in the impaired host

In general, defects in phagocytosis and in humoral or cellular immunity do not appear to predispose to the acquisition of UTI but do influence the clinical manifestations and the severity, microbiology, and complications of infection once it is established. The incidence of UTI in immunosuppressed patients other than diabetics or renal transplant recipients is not higher than the incidence in nonimmunosuppressed individuals. The higher frequencies of infection seen in diabetics and in renal transplant recipients correlate best with the duration of bladder instrumentation rather than with glycosuria or immunosuppressive regimen. Neutropenia blunts the clinical manifestations of UTI and predisposes to bacteremia. Use of broad spectrum antibiotics results in alterations in indigenous flora, promotes urinary infections with resistant nosocomial pathogens, and predisposes to fungemia with hematogenous seeding of the urinary tract. Routine screening for detection of asymptomatic bacteriuria and prompt institution of antimicrobial therapy is indicated only in renal transplant recipients within 3 months of their surgery and not in any of the other diseases discussed.

Secretory immunoglobulin A and inhibitory activity of bacterial adherence to epithelial cells in urine from patients with urinary tract infections

To assess the role of local immune response against bacterial invasion of the urinary tract we studied 168 patients with bacteriuria. Urinary secretory immunoglobulins A (sIgA) were measured using radial immunodiffusion or enzyme-linked immunosorbent assay (ELISA). In particular, ELISA is a very suitable assay for measuring the low levels of sIgA in urine. Furthermore, we used a quantitative in vitro adherence assay to investigate the attachment of Escherichia coli to human uroepithelial cells after incubation in urine from patients with urinary tract infection. Urine from patients with ileocystoplasty was significantly more potent in inhibiting bacterial adherence than was urine from other groups of patients with urinary tract infection. The presence of high urinary sIgA may help explain the increased antiadherence activity of urine in patients with ileocystoplasty. Mean urinary sIgA in patients with upper urinary tract infection was higher than in patients with uncomplicated infection in the lower urinary tract. Alterations in mucosal immune functions may account for the propensity toward bacterial colonization in women prone to uncomplicated urinary tract infection.

Adherence of uropathogenic E. coli to differentiated human uroepithelial cells grown in vitro

A quantitative in vitro model to measure E. coli adherence to differentiated human uroepithelial cells has been developed. Primary cultures of uroepithelial cells were initiated from normal ureteral epithelium. Adherence of uropathogenic 3H-labelled Escherichia coli to postconfluent human uroepithelial cells was directly related to the bacteria:epithelial cell ratio during incubation. Bacterial attachment was inhibited either by mannose or by urine containing anti-E. coli antibodies. Transmission electron microscopy showed that epithelial cells differentiated in vitro to resemble normal uroepithelium in vivo. Furthermore, electron microscopy showed specific adherence of bacteria to the glycocalyx of microvilli of the superficial uroepithelial cells in vitro in a manner which closely mimics the in vivo interaction. This model of bacterial adherence permits in vitro analysis of adhesin-receptor interactions between uropathogenic E. coli and a layer of viable uroepithelial cells similar to those lining the bladder.

Decreased immunologic responsiveness following intensified vaginal immunization against urinary tract infection

In an attempt to further increase the protective effect of vaginal immunization against urinary tract infections in Cynomolgus monkeys, the immunogen of killed E. coli was given more times, in larger amounts, and with the adjuvant MDP. Instead of increasing the protective effect, no protective effect on induced cystitis was observed. In addition, rises in urinary and serum immunoglobulins previously observed after vaginal immunization and induced cystitis were lessened. These observations appear to correspond with the classical concepts of immunologic unresponsiveness.

Urinary interleukin-2 inhibition in patients with cystitis

An inhibitor of interleukin-2 activity (IL-2-IN) is present in the urine of most patients during the acute phase of untreated bacterial cystitis (UTI). We measured urinary IL-2-IN activity in 30 adults with uncomplicated UTIs and followed the patients for an additional 6 months. Urinary IL-2-IN activity ranged between 0 and 1.97 units/mg urine creatinine (U/mg u.c.). Relatively low levels of IL-2-IN (less than 0.5 U/mg u.c.) correlated with a prior history of recurrent UTIs (p less than 0.01), and also were predictive of a subsequent UTI during the 6 month follow-up, regardless of the prior medical history (p less than 0.01). Measurement of urinary IL-2-IN during the untreated phase of a UTI may prove helpful for directing antibiotic prophylaxis against subsequent UTIs.

Mucosal IgA elaboration

Secretory IgA is the main immunoglobulin present along mucosal surfaces. It is elicited best by oral rather than parenteral administration of specific antigens. The role of antigen form on the development of a secretory IgA response is still unclear. IgA protects by preventing attachment of microorganisms or their toxic products to the surface epithelium. A wide variety of regulatory T cells are now known to be of considerable importance in optimizing the secretory IgA response. This regulation is at least partly due to the elaboration of small polypeptide products (lymphokines). These lymphokines have been shown to be key signals during the maturation of IgA precursor B cells to IgA-secreting plasma cells. By studying models of the mucosal immune system which closely approximate the natural mucosal immune response, it should be possible to develop vaccines against many pathogenic microorganisms, their toxic products, and to toxicants and carcinogens within the environment.