Immunopathogenesis of chronic pyelonephritis

Historical Incidence of Spontaneous Lesions in Kidneys from Naïve Swine Utilized In Interventional Renal Denervation Studies

The use of preclinical animal models is integral to the safety assessment, pathogenesis research, and testing of diagnostic technologies and therapeutic interventions. With inherent similarity to human anatomy and physiology, various porcine models have been the preferred preclinical model in some research areas such as medical devices, wound healing, and skin therapies. The porcine model has been the cornerstone for interventional cardiology for the evaluation and development of this catheter-based renal denervation (RDN) therapy. The porcine model provides similar vascular access and renal neurovascular anatomy to humans. In these preclinical studies, the downstream kidneys from treated arteries are assessed for possible histopathological changes in the vessel dependent territories. In assessing renal safety following RDN, it becomes critical to distinguish treatment-related changes from pre-existing background pathologies. The incidence of background pathological changes in porcine kidneys has not been previously established in normal clinically healthy. Samples from the cranial, middle, and caudal portion of 331 naïve kidneys from 181 swine were processed histologically to slides and evaluated microscopically. The most commonly encountered spontaneous changes were chronic pyelonephritis found in nearly half of the evaluated naïve kidneys (∼40 %; score 1 = 91 %, score 2 = 8.4 %, score 3 = 0.76 %) followed by chronic interstitial inflammation in 9.7 % of the kidneys (score 1 = 90.6 %, score 2 = 9.4 %). Interestingly, there were a few rare spontaneous vascular changes that could potentially affect data interpretation in interventional and toxicology studies: arteritis and arteriolar dissection. The presence of pelvic cysts was a common occurrence (6.3 %) in the kidney. The domestic swine is a widely used preclinical species in interventional research, namely in the emerging field of transcatheter renal denervation. This retrospective study presents the historical incidence of spontaneous lesions recorded in the kidneys from naive pigs enrolled in renal denervation studies. There were commonly encountered changes of little pathological consequence such as pyelonephritis or pelvic cysts and rare vascular changes such as arteritis and arteriolar dissection that were of greater potential impact on study data interpretation. These results offer a benchmark by which to gage the potential effect of a procedure or treatment on renal histopathology in swine and assist in data interpretation.

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis

Urinary tract infections (UTIs), including pyelonephritis, are among the most common and serious infections encountered in nephrology practice. UTI risk is increased in selected patient populations with renal and urinary tract disorders. As the prevalence of antibiotic-resistant uropathogens increases, novel and alternative treatment options will be needed to reduce UTI-associated morbidity. Discoveries over the past decade demonstrate a fundamental role for the innate immune system in protecting the urothelium from bacterial challenge. Antimicrobial peptides, an integral component of this urothelial innate immune system, demonstrate potent bactericidal activity toward uropathogens and might represent a novel class of UTI therapeutics. The urothelium of the bladder and the renal epithelium secrete antimicrobial peptides into the urinary stream. In the kidney, intercalated cells--a cell-type involved in acid-base homeostasis--have been shown to be an important source of antimicrobial peptides. Intercalated cells have therefore become the focus of new investigations to explore their function during pyelonephritis and their role in maintaining urinary tract sterility. This Review provides an overview of UTI pathogenesis in the upper and lower urinary tract. We describe the role of intercalated cells and the innate immune response in preventing UTI, specifically highlighting the role of antimicrobial peptides in maintaining urinary tract sterility.

Pyelonephritis in slaughter pigs and sows: morphological characterization and aspects of pathogenesis and aetiology

Background

Pyelonephritis is a serious disease in pig production that needs to be further studied. The purpose of this study was to describe the morphology, investigate the pathogenesis, and evaluate the aetiological role of Escherichia coli in pyelonephritis in slaughtered pigs by concurrent bacteriological, gross and histopathological examinations.

Methods

From Danish abattoirs, kidneys and corresponding lymph nodes from 22 slaughtered finishing pigs and 26 slaughtered sows with pyelonephritis were collected and evaluated by bacteriology and pathology. Based on gross lesions, each kidney (lesion) was grouped as acute, chronic, chronic active, or normal and their histological inflammatory stage was determined as normal (0), acute (1), sub-acute (2), chronic active (3), or chronic (4). Immunohistochemical identification of neutrophils, macrophages, T-lymphocytes, B-lymphocytes, plasma cells, E. coli and Tamm-Horsfall protein (THP) in renal sections was performed. The number of E. coli and the proportion of immunohistochemically visualized leukocytes out of the total number of infiltrating leukocytes were scored semi-quantitatively.

Results

Lesions in finishing pigs and sows were similar. Macroscopically, multiple unevenly distributed foci of inflammation mostly affecting the renal poles were observed. Histologically, tubulointerstitial infiltration with neutrophils and mononuclear cells and tubular destruction was the main findings. The significant highest scores of L1 antigen⁺ neutrophils were in inflammatory stage 1 while the significant highest scores of CD79αcy⁺ B-lymphocytes, IgG⁺ and IgA⁺ plasma cells were in stage 3 or 4. Neutrophils were the dominant leukocytes in stage 1 while CD3ε⁺ T-lymphocytes dominated in stage 2, 3 and 4. Interstitially THP was seen in 82% and 98% of kidneys with pyelonephritis from finishing pigs and sows, respectively. E. coli was demonstrated in monoculture and/or identified by immunohistochemistry in relation to inflammation in four kidneys from finishing pigs and in 34 kidneys from sows.

Conclusions

E. coli played a significant role in the aetiology of pyelonephritis. Neutrophils were involved in the first line of defence. CD3ε⁺ T-lymphocytes were involved in both the acute and chronic inflammatory response while a humoral immune response was most pronounced in later inflammatory stages. The observed renal lesions correspond with an ascending bacterial infection with presence of intra-renal reflux.

Autoimmune Responses to Tamm-Horsfall Protein in the Pathogenesis of Chronic Pyelonephritis

Although the role of bacterial infection as the major determinant in the development of acute pyelonephritis has been well documented for years, the nature of the renal scarring typical of chronic "atrophic" pyelonephritis has been a matter of controversy for at least three decades. In the past, recurrent bacterial infection of the kidney was thought to be responsible for the pathologic entity of "chronic pyelonephritis." However, more recent studies suggest that recurrent bacteriuria, in the absence of some form of obstructive uropathy, rarely produces chronic pyelonephritis. The close association between vesicoureteral reflex and chronic pyelonephritis has also been firmly established and has been observed to occur frequently in the absence of urinary tract infection. However, the mechanism by which vesicoureteral reflux injures the kidney has not been firmly established. A number of observations have suggested that some normal component of urine, particularly Tamm-Horsfall protein, might serve as an antigenic determinant involved in the immunopathogenesis of renal scarring in vesicoureteral reflux. The present studies were designed to investigate the immunopathogenic role of Tamm-Horsfall protein in a rabbit model of tubulointerstitial nephritis, and in a swine model of reflux nephropathy. The immune responses to Tamm-Horsfall protein in patients with recurrent nephrolithiasis were also examined, as were the antigenic similarities between Tamm-Horsfall protein and protein-containing components of uropathic bacteria. The results of these studies indicate that autoimmune responses to Tamm-Horsfall protein may occur after exposure to Tamm-Horsfall protein by intravenous challenge in rabbits, and by urinary reflux in pigs, as well as in recurrent nephrolithiasis in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Tamm-Horsfall protein: a multilayered defence molecule against urinary tract infection

Urinary tract infection (UTI) is the most common nonepidemic bacterial infection in humans, representing a constant danger for the host. Both innate and adaptive components of the immune system as well as stromal cells including bladder epithelium are involved in the prevention and clearance of UTI. However, the particular properties of the urogenital tract, which does not comprise typical physical barriers like a mucus or ciliated epithelium, necessitate soluble mediators with potent immunomodulatory capabilities. One candidate molecule capable of both mediating direct antimicrobial activity and alerting immune cells is the evolutionary conserved Tamm-Horsfall protein (THP). Tamm-Horsfall protein is exclusively produced by the kidney in the distal loop of Henle; however, its definite physiological function remains elusive. Mounting evidence indicates that beyond a mere direct antimicrobial activity, THP exerts potent immunoregulatory activity. Furthermore, the genetic ablation of the THP gene leads to severe infection and lethal pyelonephritis in an experimental model of UTI. Recent data are provided demonstrating that THP links the innate immune response with specific THP-directed cell-mediated immunity. In light of these novel findings we discuss the particular role of THP as a specialized defence molecule. We propose an integrated model of protective mechanisms against UTI where THP acts by two principle nonmutually exclusive mechanisms involving the capture of potentially dangerous microbes and the ability of this peculiar glycoprotein to induce robust protective immune responses against uropathogenic bacteria.

Tamm-Horsfall glycoprotein links innate immune cell activation with adaptive immunity via a Toll-like receptor-4-dependent mechanism

Tamm-Horsfall glycoprotein (THP) is expressed exclusively in the kidney and constitutes the most abundant protein in mammalian urine. A critical role for THP in antibacterial host defense and inflammatory disorders of the urogenital tract has been suggested. We demonstrate that THP activates myeloid DCs via Toll-like receptor-4 (TLR4) to acquire a fully mature DC phenotype. THP triggers typical TLR signaling, culminating in activation of NF-kappaB. Bone marrow-derived macrophages from TLR4- and MyD88-deficient mice were nonresponsive to THP in contrast to those from TLR2- and TLR9-deficient mice. In vivo THP-driven TNF-alpha production was evident in WT but not in Tlr4-/- mice. Importantly, generation of THP-specific Abs consistently detectable in urinary tract inflammation was completely blunted in Tlr4-/- mice. These data show that THP is a regulatory factor of innate and adaptive immunity and therefore could have significant impact on host immunity in the urinary tract.

Urinary excretion of brush border antigens and other proteins in children with vesico-ureteric reflux

This study was designed to evaluate the occurrence and the type of proteinuria in 82 children with vesico-ureteric reflux (VUR) with or without renal scars. The urinary excretion of the high molecular weight protein albumin was taken as an index of glomerular alterations and the excretion of retinol-binding protein (RBP), beta 2-microglobulin and brush border antigens (BBA) (measured by monoclonal antibody-based enzyme-linked immunosorbent assay) was taken as an index of tubular alterations. All such markers were increased in children with VUR and were related to the degree of renal function. Patients showing reduced creatinine clearance had very high levels of albuminuria, microproteinuria and BBA, with all these variables reciprocally correlated. In children with normal renal function however, only microproteins (not albumin or BBA) were slightly increased, thus indicating an isolated tubular defect without involvement of the proximal segment of the tubule. However, microprotein excretion did not correlate with the grade of scarring (99mtechnetium-dimercaptosuccinic acid scan), both RBP and beta 2-microglobulin excretion being normal in 75% of children with radioisotopic signs of renal lesions but increased in 17% of children without scars. Therefore, tubular proteinuria identifies different groups of children with VUR but is not related to renal scarring. Prospective studies will define the usefulness of proteinuria as a reliable indicator of renal outcome.

Natural history of "lower" urinary tract infections

Our current knowledge of the long-term outcome of uncomplicated urinary tract infections in women is based on a re-evaluation of the criteria for defining pyelonephritis at autopsy, careful description of the causes of renal disease among patients entering dialysis and transplant programs, long term observation of patients, and epidemiologic studies which have attempted to determine the association of bacteriuria with mortality. The weight of the evidence favors the conclusion that although urinary tract infections can produce severe impairment of renal function, this is rare in the absence of a major predisposing factor such as obstruction, calculus, reflux, abnormalities of the voiding mechanism or diabetes. The predisposing lesions, however, may go undetected until heralded by episodes of acute pyelonephritis or by renal failure. Unfortunately, urinary tract infections are so common that it is difficult to distinguish the population at greatest risk. The possible role of renal damage produced by autoimmune mechanisms following infection needs continued study.

Extratubular Tamm-Horsfall protein deposits induced by ureteral obstruction in mice

The effects of unilateral ureteral obstruction were studied in mice. Obstruction for 24 hr led to the formation of extratubular Tamm-Horsfall protein (TH) aggregates within the renal interstitium and at the base of distal convoluted tubular (DCT) cells. These DCT deposits were shown by ultrastructural analysis to be entirely extracellular. They had the fibrillar substructure characteristic of TH and had not been seen after urinary obstruction in other species. As a consequence of retrograde flow of urine to glomeruli, obstruction also caused TH aggregates to form within Bowman's spaces. These glomerular casts of TH were detected throughout the 3-week period of study after the release of unilateral obstruction. High serum titers of IgG antibodies to TH developed in mice intradermally immunized with TH but were not observed after obstruction alone. Circulating anti-TH antibodies combined with TH present on the basal surfaces of the thick ascending limb of the loop of Henle cells and DCT cells to form immune complexes in situ. Interstitial inflammation in the areas surrounding subepithelial tubular immune deposits was not present in the kidneys of immunized mice and was not selectively induced by temporary obstruction. However, foci of inflammation were seen in all obstructed kidneys. At later times, inflammatory foci in previously obstructed kidneys were associated with progressive scarring, primarily in polar regions. The location and severity of these changes within kidneys produced by obstruction in immunized mice did not differ from those in unimmunized mice. The titers of anti-TH antibodies in immunized mice were not enhanced or depressed as a consequence of unilateral ureteral obstruction. These studies demonstrate that complete obstruction of urinary flow in the mouse for periods as short as 24 hr may lead to progressive segmental renal scarring. These studies further indicate that increasing the quantities of extracellular TH by obstruction does not facilitate inflammatory responses to TH immune complexes formed in situ. While exposure of renal tissue to highly toxic components of extravasated urine may play a crucial role in inflammatory responses, autoimmunity to TH was not implicated as a contributing factor by the present studies in mice.

The inflammatory response and tissue damage. The example of renal scars following acute renal infection

Most clinical and experimental evidence suggests that renal scarring occurs following urinary tract infections in those patients with an abnormality of the urinary tract or kidney function. Experimentally, bacterial multiplication within the kidney occurs only in the presence of obstruction, leading rapidly to acute exudative pyelonephritis and invariably to kidney scars within weeks. Various manipulations of the bacterial load and/or of the inflammatory response during acute pyelonephritis have demonstrated that the inflammatory processes, not the bacterial component of pyelonephritis, are responsible for permanent renal tissue damage. Polymorphonuclear leucocytes (PMNLs) infiltrating the kidney tissue during acute pyelonephritis appear to release metabolites that are toxic to the parenchyma. Indeed, both the prevention of PMNL influx into renal tissue, by means of colchicine or cyclophosphamide, and the inactivation of some of their toxic metabolites, by means of dapsone, have led to the prevention of tissue damage and kidney scars. However, the most potent protective activity was observed with early antibiotic treatment, which stopped bacterial multiplication and prevented the early influx of PMNLs, thus preventing tissue damage and scar formation. Similar observations have been made in children with acute pyelonephritic episodes, in whom early and aggressive antibiotic treatment prevented subsequent kidney scars, while delayed treatment did not.

Serum antibody against Tamm-Horsfall protein in patients with renal cell carcinoma

We assayed sera from 24 patients with metastatic renal cell carcinoma for class specific antibody against urinary Tamm-Horsfall protein (THP) using indirect solid-phase radioimmunoassay techniques. Overall, 16 patients had elevated antibody levels (greater than 2 SD above the mean levels of control subjects). IgG against THP was elevated in eight of the patients, IgA in 12, and IgM in five. However, THP was not identifiable by immunohistochemical techniques in the sections of 15 of 24 tumors available for study. Nine of the 15 tumors were from patients with elevated antibody levels. Serum antibody against THP in patients with renal cell carcinoma appears to result from antigenic stimulation by THP derived from the urine rather than from the neoplasm.

Reflux nephropathy

This article reviews current concepts of reflux nephropathy, including the pathophysiology, diagnosis, relationship to infection, role in causing end-stage renal disease, and appropriate treatment and management. The condition is defined from a epidemiologic point of view herein, and attention also is given to possible progressions this condition can take.

Interaction of Tamm-horsfall protein with bacterial extracts

Crude extracts of uropathic Escherichia coli have been reported to inhibit the binding of human Tamm-Horsfall protein (THP) to homologous and heterologous anti-THP antibody in immunoassays. This phenomenon was believed to be due to immunologic cross reactivity between THP and the bacterial antigens for the same antibody. Our attempts to further purify and characterize these "cross reactive" antigens with ion exchange and molecular sieve chromatography were unsuccessful. When purified anti-THP antibody was conjugated to sepharose beads forming an immunoadsorption column capable of isolating THP and cross reactive antigens from solution, the bacterial extracts did not react with the affinity column. However, binding between THP and the bacterial extracts and between THP and whole bacteria were demonstrated. These findings suggest that the cross reactivity seen in the immunoassays is caused by the interaction between the bacterial extracts and THP, and is not representative of true immunologic cross reaction for a common antibody.

Characterization of monoclonal antibodies specific for human Tamm-Horsfall protein

Fifteen monoclonal antibodies have been produced to human Tamm-Horsfall protein (THP), identifying at least seven distinct epitopes. The antibodies have been used to isolate from serum an immunoreactive protein which comigrates with urinary THP. In addition, the antibodies may prove useful to set up an immunoenzymoassay for urinary THP as well as for immunoaffinity purification.

Effect of Tamm-Horsfall urinary glycoprotein on phagocytosis and killing of type I-fimbriated Escherichia coli

Human polymorphonuclear leukocytes (PMN) ingest type I (mannose sensitive) fimbriated Escherichia coli even in the absence of antibody, complement, or other serum opsonins. Our studies suggest that the Tamm-Horsfall urinary glycoprotein (THP) interferes with serum-independent ingestion. Electron micrographs showed that dissolved THP adhered to type I fimbriae and formed a pseudocapsule around bacteria bearing type I fimbriae. Phase-variant bacteria grown on blood agar neither expressed fimbriae nor bound THP. Affinity column chromatography demonstrated mannose-sensitive binding between purified type I fimbriae and purified THP. The ability of human PMN to bind and ingest type I-fimbriated E. coli was diminished if the bacteria had been coated by exposure to THP at physiologic concentrations. At 1 h, PMN were associated with an average of 2.62 uncoated bacteria, but with only 0.18 coated bacteria (P less than 0.001). alpha-Methyl mannoside blocked the observed effect of THP on binding and phagocytosis in a dose-dependent fashion: increased mannoside led to increased blocking. PMN preincubated with THP were able to bind and phagocytose normally. There did not appear to be any significant clumping of bacteria in suspension to account for these effects. Bactericidal assays with leukocytes in suspension demonstrated protection of THP-coated bacteria. At 1 h, PMN killed 42% of noncoated E. coli (a decrease of 0.24 log), but the number of THP-coated bacteria increased by 75% (an increase of 0.24 log). These observations may partially explain the virulence of E. coli in the bladder and kidney, where serum activity is low and THP is abundant.

A system for accurate immunolocalization of Tamm-Horsfall protein in renal biopsies

The distribution of Tamm-Horsfall protein (THP) was studied in the human kidney using formalin-fixed, paraffin-embedded sections with a monoclonal antibody specific for human THP applied in conjunction with a modified dinitrophenyl hapten sandwich staining (DHSS) procedure. The method was found to be highly sensitive producing very strong specific staining at antibody dilutions up to 1 in 64 000. Counterstaining with Haematoxylin and Eosin was possible without significant masking of the specific staining. This provided excellent structural definition of the background tissue which proved especially important in the study of THP localization in randomly oriented biopsy material. THP was found in all segments of the thick ascending limbs of loops of Henle, most segments of distal convoluted tubules and occasionally in distended collecting ducts and in the glomerular capsular space. Maculae densae did not contain THP. The combination of the modified DHSS procedure and the human THP specific antibody represents a highly sensitive and reliable method for specific staining of the THP in kidney sections.

Vesicoureteral reflux and reflux nephropathy

Vesicoureteral reflux (VUR) is mainly a primary phenomenon due to incompetence of the ureterovesical junction, mostly affecting a pediatric population. During micturition cystourethrography (MCU) reflux into the kidney--intrarenal reflux (IRR)--is occasionally seen. In areas with IRR the kidney surface may subsequently be depressed and the papillae retracted (reflux nephropathy (RN]. VUR may lead to hypertension and/or end-stage renal failure. Most commonly, VUR is discovered during evaluation for urinary tract infection, but it may also be present in patients with hypertension, toxemia of pregnancy, chronic renal failure and proteinuria, and it may be found in siblings of patients with VUR. For the time being VUR is demonstrated at radiographic MCU, whereas RN is diagnosed by demonstration of focal scars and of abnormal parenchymal thickness at urography. In children with VUR and no abnormalities of calyces or parenchymal defects standardized measurement of the parenchymal thickness at three sites may identify kidneys which are likely to develop focal scars. Quantitation of focal scarring should be performed in connection with a measure of the overall kidney size. The occurrence of IRR is dependent of the papillary morphology, intrapelvic pressure and urine flow. There may be an important relationship between renal ischemia and IRR in producing a 'vicious circle of deleterious effects' which, combined with parenchymal extravasation, may lead to RN. Treatment of VUR includes medical and surgical management. Since renal scarring may occur in infancy, prevention should focus on infants and young children. Infants and young children with severe VUR may have normal urograms. Therefore a MCU should also be performed, preferably with the recommended standardized technique.

Host factors in the pathogenesis of urinary tract infections

Classic animal studies conducted two decades ago provided the basic understanding of the pathogenesis of urinary tract infections. Those studies emphasized the natural resistance of the urinary tract to colonization and infection. Urinary obstruction, stasis, and reflux remain of great importance in all age groups in predisposing to infection. Recent studies of the crucial role of bacterial adherence to epithelial cells lining the genitourinary tract have shed new light on the pathogenesis of urinary infection. Information from adherence studies may have considerable clinical relevance with regard to the development of vaccines that prevent bacterial invasion particularly in the upper urinary tract. The normal defense mechanisms present in the human urinary tract are discussed. Despite progress in our understanding of the pathogenesis of urinary infection, considerable controversy still exists particularly with regard to host susceptibility to recurrent lower urinary tract infections in women with anatomically normal urinary tracts. Recent studies also have emphasized the significance of the host's normal immunologic mechanisms in contributing to intrinsic renal damage after upper urinary tract invasion by bacteria.

Current concepts in the management of urinary tract infections in adults

This article discusses the pathogenesis, etiology, and diagnosis of bacterial urinary tract infections. Initial therapy is outlined, as is the treatment of recurrent infections.