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

99mTechnetium-dimercaptosuccinic acid scan in the diagnosis of acute pyelonephritis in children: relation to clinical and radiological findings

Seventy-two children, 59 girls and 13 boys, 0.1-15.9 (median 1.1) years of age, with acute pyelonephritis (APN) were investigated with the aid of a dimercaptosuccinic acid (DMSA) scan, renal ultrasonography (US) and a desmopressin test within 5 days of admission. Sixty-two children were reinvestigated approximately 2 months later when intravenous urography (IVU) and micturition cysto-urethrography were also performed. During infection, 92% of the children showed changes in the DMSA scan with 69% by US, and the two investigations agreed in 58% of the kidneys. At follow-up, 68% showed changes in the DMSA scan, 47% by US and 48% by IVU. The DMSA scan and IVU agreed in 60% of the kidneys. Twenty-nine percent of the children had vesico-ureteric reflux (VUR). The presence of grade greater than or equal to 3 VUR was associated with greater defects on the DMSA scan during infection, and at follow-up with a higher frequency of persistent changes compared with no VUR (P less than 0.02 and 0.01, respectively). During infection the size of the defect on the DMSA scan correlated with renal volume and C-reactive protein and inversely with the glomerular filtration rate, and at follow-up it correlated inversely with the renal concentration capacity. The DMSA scan is a sensitive method for diagnosing and localizing APN in children, and findings on DMSA scan show a weak but significant correlation with routine clinical and radiological parameters. It is suggested that persistent renal damage after APN in children without VUR may be more common than previously assumed.

Reactive oxygen molecules, oxidant injury and renal disease

Oxidant injury has been implicated in the pathogenesis of inflammatory, metabolic and toxic insults, in ischemic-reperfusion injury, and in carcinogenesis, aging and atherosclerosis. Oxidant injury is initiated by free radicals and reactive oxygen molecules which are generated by activated neutrophils, monocytes, and mesangial cells, during normal and abnormal metabolic processes, and from the metabolism of exogenous drugs and toxins. When cells and organs are exposed to oxidant stress, several different antioxidant defense mechanisms operate to prevent or limit oxidant injury. When antioxidant defense mechanisms are decreased, or when the generation of reactive oxygen molecules is increased, oxidant injury results from the shift in the oxidant/antioxidant balance. Oxidant-induced alterations of proteins, membranes, DNA, and basement membranes leads to cell and organ dysfunction. Several renal diseases including glomerulonephritis, vasculitis, toxic nephropathies, pyelonephritis, acute renal failure, and others are likely to be mediated at least in part by oxidant injury. In the future, mechanisms to decrease the generation of reactive oxygen molecules and/or antioxidant therapy may develop into new avenues of therapeutic intervention.

Bacterial attachment as a predictor of renal abnormalities in boys with urinary tract infection

The development of renal scarring was analyzed prospectively in 241 boys with their first known episode of symptomatic urinary tract infection (140 acute pyelonephritis, 61 acute cystitis, and 40 nonspecific). Of 197 boys undergoing urography, 22 (11%) had scars; 20 were in the pyelonephritis group. Vesicoureteral reflux occurred in 81% of those with scarring, compared with 20% of those without scarring. The bacteria causing the first episode of urinary tract infection in each patient were saved, and Escherichia coli organisms were characterized for the expression of both galactose-alpha (1----4)galactose-beta (Gal-Gal)-specific adhesins and pap homologous DNA. Scarring occurred in 41% and other renal abnormalities in 11% of boys infected with bacteria that did not bind Gal-Gal (Gal-Gal negative), compared with 5% and 1%, respectively, in those infected with Gal-Gal-binding strains (Gal-Gal-positive) (relative risk 8.3; 95% confidence limits 3.3 to 20.4; p less than 0.001). That boys infected with Gal-Gal-negative strains more often had reflux did not explain the increased risk for renal scarring in this group. The possibility that the phenotypically negative strains could be induced to express Gal-Gal adhesions in vivo was excluded by dot blot analysis, which showed the absence of pap homologous DNA in all but one of the Gal-Gal-negative strains. The results suggest that the absence of Gal-Gal-specific adhesins in E. coli can be used as an indicator of risk for renal scarring and the need for radiologic examination.

Host parasite interaction in urinary tract infection

The last decade has provided new insight into the mechanisms of host-parasite interactions in the urinary tract. Reduction of host resistance appears to reduce the requirement for bacterial virulence, whereas the resistant host becomes infected with bacteria of high virulence. In the resistant host, bacterial virulence can be defined as the sum of properties required to colonize the urinary tract and induce tissue reactions. The ability to attach to uroepithelial cells is the single property most frequently associated with pyelonephritogenic clones. Attachment to the Gal alpha 1-4Gal beta-containing receptors promotes localization of bacteria to the kidney and the induction of lipopolysaccharide-mediated inflammation. Other virulence factors, defined by increased frequency in acute pyelonephritis compared with asymptomatic bacteriuria, include haemolysin and aerobactin production. Among the factors which influence the natural resistance to urinary tract infection are urinary flow and reactivity to endotoxin. The resistance induced by natural exposure to infection or immunization may be protective in experimental models, but the importance of this is not yet defined. The localization, severity and sequelae of urinary tract infection are determined by the balance between bacterial virulence and host resistance. Although disease is a result of the interaction between bacterial virulence and host resistance, these components are discussed separately for clarity.