Neutrophil elastases and haemolytic uraemic syndrome

Tissue-resident macrophages mediate neutrophil recruitment and kidney injury in shiga toxin-induced hemolytic uremic syndrome

Enterohaemorrhagic E. coli cause major epidemics worldwide with significant organ damage and very high percentages of death. Due to the ability of enterohaemorrhagic E. coli to produce shiga toxin these bacteria damage the kidney leading to the hemolytic uremic syndrome. A therapy against this serious kidney disease has not been developed yet and the impact and mechanism of leukocyte activation and recruitment are unclear. Tissue-resident macrophages represent the main leukocyte population in the healthy kidney, but the role of this important cell population in shiga toxin-producing E. coli-hemolytic uremic syndrome is incompletely understood. Using state of the art microscopy and mass spectrometry imaging, our preclinical study demonstrated a phenotypic and functional switch of tissue-resident macrophages after disease induction in mice. Kidney macrophages produced the inflammatory molecule TNFα and depletion of tissue-resident macrophages via the CSF1 receptor abolished TNFα levels in the kidney and significantly diminished disease severity. Furthermore, macrophage depletion did not only attenuate endothelial damage and thrombocytopenia, but also activation of thrombocytes and neutrophils. Moreover, we observed that neutrophils infiltrated the kidney cortex and depletion of macrophages significantly reduced the recruitment of neutrophils and expression of the neutrophil-attracting chemokines CXCL1 and CXCL2. Intravital microscopy revealed that inhibition of CXCR2, the receptor for CXCL1 and CXCL2, significantly reduced the infiltration of neutrophils and reduced kidney injury. Thus, our study shows activation of tissue-resident macrophages during shiga toxin-producing E. coli-hemolytic uremic syndrome leading to the production of disease-promoting TNFα and CXCR2-dependent recruitment of neutrophils.

Enterohemorrhagic Escherichia coli Pathogenesis and the Host Response

Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain capable of causing watery or bloody diarrhea, the latter termed hemorrhagic colitis, and hemolytic-uremic syndrome (HUS). HUS is defined as the simultaneous development of non-immune hemolytic anemia, thrombocytopenia, and acute renal failure. The mechanism by which EHEC bacteria colonize and cause severe colitis, followed by renal failure with activated blood cells, as well as neurological symptoms, involves the interaction of bacterial virulence factors and specific pathogen-associated molecular patterns with host cells as well as the host response. The innate immune host response comprises the release of antimicrobial peptides as well as cytokines and chemokines in addition to activation and/or injury to leukocytes, platelets, and erythrocytes and activation of the complement system. Some of the bacterial interactions with the host may be protective in nature, but, when excessive, contribute to extensive tissue injury, inflammation, and thrombosis, effects that may worsen the clinical outcome of EHEC infection. This article describes aspects of the host response occurring during EHEC infection and their effects on specific organs.

Promoter sequence of Shiga toxin 2 (Stx2) is recognized in vivo, leading to production of biologically active Stx2

Shiga toxins (Stx) are the main agent responsible for the development of hemolytic-uremic syndrome (HUS), the most severe and life-threatening systemic complication of infection with enterohemorrhagic Escherichia coli (EHEC) strains. We previously described Stx2 expression by eukaryotic cells after they were transfected in vitro with the stx₂ gene cloned into a prokaryotic plasmid (pStx2). The aim of this study was to evaluate whether mammalian cells were also able to express Stx2 in vivo after pStx2 injection. Mice were inoculated by hydrodynamics-based transfection (HBT) with pStx2. We studied the survival, percentage of polymorphonuclear leukocytes in plasma, plasma urea levels, and histology of the kidneys and the brains of mice. Mice displayed a lethal dose-related response to pStx2. Stx2 mRNA was recovered from the liver, and Stx2 cytotoxic activity was observed in plasma of mice injected with pStx2. Stx2 was detected by immunofluorescence in the brains of mice inoculated with pStx2, and markers of central nervous system (CNS) damage were observed, including increased expression of glial fibrillary acidic protein (GFAP) and fragmentation of NeuN in neurons. Moreover, anti-Stx2B-immunized mice were protected against pStx2 inoculation. Our results show that Stx2 is expressed in vivo from the wild stx₂ gene, reproducing pathogenic damage induced by purified Stx2 or secondary to EHEC infection.

Enterohemorrhagic Shiga toxin (Stx)-producing Escherichia coli (EHEC) infections are a serious public health problem, and Stx is the main pathogenic agent associated with typical hemolytic-uremic syndrome (HUS). In contrast to the detailed information describing the molecular basis for EHEC adherence to epithelial cells, very little is known about how Stx is released from bacteria in the gut, reaching its target tissues, mainly the kidney and central nervous system (CNS). In order to develop an efficient treatment for EHEC infections, it is necessary to understand the mechanisms involved in Stx expression. In this regard, the present study demonstrates that mammals can synthesize biologically active Stx using the natural promoter associated with the Stx-converting bacteriophage genome. These results could impact the comprehension of EHEC HUS, since local eukaryotic cells transduced and/or infected by bacteriophage encoding Stx2 could be an alternative source of Stx production.

The functional state of neutrophils correlates with the severity of renal dysfunction in children with hemolytic uremic syndrome

Hemolytic Uremic Syndrome (HUS) is the main cause of acute renal failure in children. The high percentage of patients who develop long-term sequelae constitutes an important medical concern. The identification of parameters that correlate with the degree of renal failure may be useful to plan the best treatment soon after hospitalization. Here, we investigated the functional state of neutrophils (PMN) from HUS patients on admission, before dialysis and/or transfusion, in relation to the severity of renal impairment reached during the acute period (AP). We found that all PMN activation parameters measured in severe cases of HUS (HUS AP3) were statistically lower comparing to children with mild cases of HUS (HUS AP1). As HUS PMN phenotype and dysfunction is compatible with that of cells undergoing cell death, we also studied spontaneous apoptosis. Not only were HUS PMN not apoptotic, but HUS AP3 PMN showed an increased survival. Almost all phenotypic and functional parameters measured on PMN correlated with severity. Our results revealed a marked deactivation of PMN in severe cases of HUS, and suggest that studying the functional state of PMN could be of prognostic value.

Relevance of neutrophils in the murine model of haemolytic uraemic syndrome: mechanisms involved in Shiga toxin type 2-induced neutrophilia

It has been demonstrated that infections due to Shiga toxins (Stx) producing Escherichia coli are the main cause of the haemolytic uraemic syndrome (HUS). However, the contribution of the inflammatory response in the pathogenesis of the disease has also been well established. Neutrophils (PMN) represent a central component of inflammation during infections, and patients with high peripheral PMN counts at presentation have a poor prognosis. The mouse model of HUS, by intravenous injection of pure Stx type 2 (Stx2), reproduces human neutrophilia and allows the study of early events in the course of Stx2-induced pathophysiological mechanisms. The aim of this study was to address the contribution of PMN on Stx2 toxicity in a murine model of HUS, by evaluating the survival and renal damage in mice in which the granulocytic population was depleted. We found that the absence of PMN reduced Stx2-induced lethal effects and renal damage. We also investigated the mechanisms underlying Stx2-induced neutrophilia, studying the influence of Stx2 on myelopoyesis, on the emergence of cells from the bone marrow and on the in vivo migration into tissues. Stx2 administration led to an accelerated release of bone marrow cells, which egress at an earlier stage of maturation, together with an increase in the proliferation of myeloid progenitors. Moreover, Stx2-treated mice exhibited a lower migratory capacity to a local inflammatory site. In conclusion, PMN are essential in the pathogenesis of HUS and neutrophilia is not merely an epiphenomenon, but contributes to Stx2-damaging mechanism by potentiating Stx2 toxicity.

Impaired neutrophils in children with the typical form of hemolytic uremic syndrome

Experimental and clinical evidence suggest that activated neutrophils (PMN) could contribute to endothelial damage in Hemolytic Uremic Syndrome (D+HUS). Additionally, while PMN-activating cytokines and PMN-derived products have been found in D+HUS sera, we have demonstrated phenotypic alterations in D+HUS PMN compatible with a deactivation state. Here, we investigated whether D+HUS PMN were actually hyporesponsive, and explored some of the mechanisms probably involved in their derangement. Twenty-two D+HUS children were bled in the acute period, and blood samples from healthy, acute uremic and neutrophilic children were obtained as controls. We evaluated degranulation markers in response to cytokines, intracellular granule content, and reactive oxygen species (ROS) generation in circulating D+HUS and control PMN. The influence of D+HUS-derived plasma and the direct effects of Stx in vitro were evaluated on healthy donors' PMN. We found that D+HUS PMN presented reduced degranulatory capacity in response to cytokines and intracellular granule content, and decreased ROS generation. D+HUS plasma or Stx did not affect the phenotype and function of healthy donors' PMN. These results suggest that upon hospitalization D+HUS PMN are functionally impaired and show features of previous degranulation, indicating a preceding process of activation with release of ROS and proteases involved in endothelial damage.

Protective role of nitric oxide in mice with Shiga toxin-induced hemolytic uremic syndrome

BACKGROUND

Nitric oxide (NO) is an endogenous vasodilator and platelet inhibitor. An enhanced NO production has been detected in patients with hemolytic uremic syndrome (HUS), although its implication in HUS pathogenesis has not been clarified.

METHODS

A mouse model of Shiga toxin 2 (Stx2)-induced HUS was used to study the role of NO in the development of the disease. Modulation of l-arginine-NO pathway was achieved by oral administration of NO synthase (NOS) substrate or inhibitors, and renal damage, mortality and platelet activity were evaluated. The involvement of platelets was studied by means of a specific anti-platelet antibody.

RESULTS

Inhibition of NO generation by the NOS inhibitor L-NAME enhanced Stx2-mediated renal damage and lethality; this effect was prevented by the addition of l-arginine. The worsening effect of L-NAME involved enhanced Stx2-mediated platelet activation, and it was completely prevented by platelet depletion.

CONCLUSIONS

NO exerts a protective role in the early pathogenesis of HUS, and its inhibition potentiates renal damage and mortality through a mechanism involving enhanced platelet activation.

Pathogenesis of Shiga toxin-associated hemolytic uremic syndrome

The aim of this review is to examine recent advances in experimental and clinical research relevant to the pathogenesis of diarrhea-associated hemolytic uremic syndrome with special reference to histopathologic findings, virulence factors of Shiga toxin-producing Escherichia coli, the host response, and the prothrombotic state. Despite significant advances during the past decade, the exact mechanism by which Shiga toxin-producing E. coli leads to hemolytic uremic syndrome remains unclear. Factors such as Shiga toxin, lipopolysaccharide, the adhesins intimin and E. coli-secreted proteins A, B, and D, the 60-MD plasmid, and enterohemolysin likely contribute to the pathogenesis. Data on the inflammatory response of the host, including leukocytes and inflammatory mediators, are updated. The pathogenesis of the prothrombotic state leading to thrombocytopenia secondary to endothelial cell damage and platelet activation is also discussed. A hypothetical sequence of events from ingestion of the bacteria to the development of full-blown hemolytic uremic syndrome is proposed.

Soluble Fas and soluble Fas-ligand in children with Escherichia coli O157:H7-associated hemolytic uremic syndrome

We measured soluble Fas-ligand (sFas-L) and soluble Fas (sFas) levels by sandwich enzyme-linked immunosorbeny assay and compared them among (1) healthy controls (n = 11), (2) children with hemorrhagic colitis (HC) caused by a non-verotoxin-producing pathogen (n = 23), (3) patients with uncomplicated Escherichia coli O157:H7 HC (n = 14), and (4) children with O157:H7-associated hemolytic uremic syndrome (HUS) (n = 24). Children with uncomplicated E coli O157:H7 HC and HUS were matched for duration of enteric prodrome before blood sample collection. We also compared sFas-L and sFas levels among patients with HUS according to severity of renal dysfunction; abnormally increased sFas-L levels were noted in only 4% of the children (n = 3). Abnormally high concentrations of sFas were noted in 9% of the children with HC caused by a non-verotoxin-producing pathogen, 29% of the patients with uncomplicated E coli O157:H7 HC, and 69% of the children with O157:H7-associated HUS. Compared with healthy controls, patients with HUS had twofold greater concentrations of sFas (P: < 0.0001). Levels of sFas were not statistically different between 14 patients with uncomplicated O157:H7 HC and 14 children with HUS (8.2 +/- 4.7 versus 11.0 +/- 4.6 U/mL, respectively; P: < 0.07) when matched for time after onset of enteritis (7.0 +/- 3.7 versus 7.3 +/- 3.8 days, respectively). Greater concentrations of sFas were noted in patients with HUS who developed oligoanuria (n = 10; P: < 0.007), required peritoneal dialysis (n = 10; P: < 0.007), or had a decreased glomerular filtration rate (n = 5; P: < 0.002) 1 year later. Our data show that plasma concentrations of sFas but not sFas-L are abnormally increased in children with O157:H7 infections. Levels of sFas are associated with severity of renal dysfunction during HUS. Further studies are needed to clearly determine the role and origin of circulating sFas among children with infections caused by E coli O157:H7.

Leukocytosis in children with Escherichia coli O157:H7 enteritis developing the hemolytic-uremic syndrome

BACKGROUND

Fewer than 10% of children with Escherichia coli O157:H7 enteritis develop hemolytic-uremic syndrome (HUS).

OBJECTIVE

To determine whether circulating leukocytes are independent risk markers of developing HUS during E. coli O157:H7 enteritis.

METHODS

We reviewed the charts of all children with culture-proved E. coli O157:H7 infections seen at Sainte-Justine Hospital between 1987 and 1997. Epidemiologic data, laboratory indices and circulating leukocytes counts were noted. HUS diagnosis was validated with independent HUS patient lists from the pediatric nephrology services of tertiary care hospitals in the Montreal metropolitan area. The date of onset of enteritis was determined by two independent observers. Leukocyte counts were compared among the following independent groups: (1) uncomplicated O157:H7 enteritis (Group 1); (2) O157:H7 enteritis with the subsequent development of HUS (Group 2); (3) HUS already present at the time of medical consultation (Group 3).

RESULTS

There were 369 children with E. coli O157:H7 infection. A complete blood count was not performed in 114 (31%) patients. Observers disagreed on the date of onset of gastroenteritis in 34 (9%) children only (kappa 0.92). The study population thus included 221 patients: Group 1, n = 161; Group 2, n = 27; and Group 3, n = 33. Patients developing HUS (Group 2) presented greater total leukocyte (P < 0.008), polymorphonuclear (P < 0.008) and monocyte (P < 0.07) counts than those with an uncomplicated course (Group 1). Logistic regression analysis showed that young age [odds ratio (OR), 0.98; 95% confidence interval (CI), 0.96 to 0.99], duration of enteric prodrome < or =3 days (OR 4.8, 95% CI 1.13 to 20.7) and initial leukocytosis (OR 1.22, 95% CI, 1.11 to 1.35) were independent predictors of HUS.

CONCLUSIONS

Based on the variables identified above, further studies are needed to determine whether the inflammatory response of the host represents only a marker of the severity of gastrointestinal infection or whether, alternatively, it is a pathophysiologic factor that leads to HUS.

Shiga toxin-2 induces neutrophilia and neutrophil activation in a murine model of hemolytic uremic syndrome

It has been demonstrated that infections due to Shiga toxins (Stx) producing Escherichia coli are the main cause of the hemolytic uremic syndrome (HUS). Although it is recognized that Stx damage the glomerular endothelium, clinical and experimental evidence suggests that the inflammatory response is able to potentiate Stx toxicity. Lipopolysaccharides (LPS) and neutrophils (PMN) represent two central components of inflammation during a gram-negative infection. In this regard, patients with high peripheral PMN counts at presentation have a poor prognosis. Since the murine model has been used to study LPS-Stx interactions, we analyzed the effects of Stx alone or in combination with LPS on the kinetics of neutrophil production and activation and their participation in renal damage. We observed a sustained neutrophilia after Stx2 injection. Moreover, these neutrophils showed increased expression of CD11b, enhanced cytotoxic capacity, and greater adhesive properties. Regarding the cooperative effects of LPS on Stx2 action, we demonstrated potentiation of neutrophilia and CD11b induction at early times by pretreatment with LPS. Finally, a positive correlation between neutrophil percentage and renal damage (assayed as plasmatic urea) firmly suggests a role for PMN in the pathogenesis of HUS.

Increased Fragmentation of von Willebrand Factor, Due to Abnormal Cleavage of the Subunit, Parallels Disease Activity in Recurrent Hemolytic Uremic Syndrome and Thrombotic Thrombocytopenic Purpura and Discloses Predisposition in Families

We investigated here the changes in von Willebrand factor (vWF) multimers in recurrent, sporadic and familial forms of hemolytic uremic syndrome (HUS)/thrombotic thrombocytopenic purpura (TTP) to see whether they are actually proteolyzed in vivo in these patients. Molecular determinants of fragments in vWF were also characterized to identify possible sites of cleavage of the subunit. Unusually large vWF multimers were found in blood of 8 of 10 patients with recurrent HUS/TTP, both in the acute phase and in remission, but never in familial and sporadic cases. Instead, all of the groups showed evidence of enhanced fragmentation of vWF multimers during the acute phase. Increased fragmentation was also shown by decrease in native 225-kD vWF subunit. In recurrent and sporadic HUS/TTP, enhanced fragmentation normalized at remission, but the abnormality persisted in familial HUS/TTP patients. The latter findings suggest that patients with familial HUS/TTP may have a congenital abnormality in vWF processing. Analysis with specific monoclonal antibodies showed the presence of the normal vWF fragments with apparent molecular mass of 189, 176, and 140 kD in all patients; however, in 6 recurrent and in 5 familial cases, novel fragments that differed in size from normal ones were found. The size of these abnormal fragments differed from one patient to another and none of them was ever found in normal plasma. These results documented, for the first time in HUS/TTP, an abnormal cleavage of the vWF subunit that might account for the increased fragmentation observed in these patients.

Increased Fragmentation of von Willebrand Factor, Due to Abnormal Cleavage of the Subunit, Parallels Disease Activity in Recurrent Hemolytic Uremic Syndrome and Thrombotic Thrombocytopenic Purpura and Discloses Predisposition in Families

We investigated here the changes in von Willebrand factor (vWF) multimers in recurrent, sporadic and familial forms of hemolytic uremic syndrome (HUS)/thrombotic thrombocytopenic purpura (TTP) to see whether they are actually proteolyzed in vivo in these patients. Molecular determinants of fragments in vWF were also characterized to identify possible sites of cleavage of the subunit. Unusually large vWF multimers were found in blood of 8 of 10 patients with recurrent HUS/TTP, both in the acute phase and in remission, but never in familial and sporadic cases. Instead, all of the groups showed evidence of enhanced fragmentation of vWF multimers during the acute phase. Increased fragmentation was also shown by decrease in native 225-kD vWF subunit. In recurrent and sporadic HUS/TTP, enhanced fragmentation normalized at remission, but the abnormality persisted in familial HUS/TTP patients. The latter findings suggest that patients with familial HUS/TTP may have a congenital abnormality in vWF processing. Analysis with specific monoclonal antibodies showed the presence of the normal vWF fragments with apparent molecular mass of 189, 176, and 140 kD in all patients; however, in 6 recurrent and in 5 familial cases, novel fragments that differed in size from normal ones were found. The size of these abnormal fragments differed from one patient to another and none of them was ever found in normal plasma. These results documented, for the first time in HUS/TTP, an abnormal cleavage of the vWF subunit that might account for the increased fragmentation observed in these patients.

Inflammatory mediators in Escherichia coli O157:H7 hemorrhagic colitis and hemolytic-uremic syndrome

BACKGROUND

Recent experimental data suggest that the inflammatory response of the host to verotoxin and/or lipopolysaccharides of Escherichia coli is involved in the pathophysiology of verotoxin-producing E. coli (VTEC) infections.

METHODS

We measured the circulating concentrations of cytokines [TNF-alpha, interleukin (IL)-1-beta, IL-1 receptor antagonist (Ra), IL-6, IL-8, IL-10] and soluble leukocyte adhesion molecules (L-selectin, P-selectin, E-selectin, intracellular cell adhesion molecule-1, vascular cell adhesion molecule-1) by sandwich enzyme-linked immunosorbent assay among (1) normal controls (n = 12), (2) disease controls with hemorrhagic colitis (HC) not associated with VTEC infections (n = 57), (3) patients with uncomplicated HC caused by E. coli O157:H7 (n = 30), and (4) children with hemolytic-uremic syndrome (HUS) (n = 28). Patients with HUS were matched with children who presented an uncomplicated HC caused by E. coli O157:H7 for the time interval elapsed between the onset of HC and that of blood sample collection.

RESULTS

Concentrations of TNF-alpha and IL-1-beta were undetectable. Children with HUS were characterized by increased amounts of IL-6 and IL-8, lower values of soluble L-selectin as well as increased levels of IL-10 and IL-1Ra. The circulating concentrations of IL-1Ra were higher among children with O157:H7 HC who subsequently developed HUS.

CONCLUSIONS

Increased pro- and antiinflammatory cytokine responses are produced by the host during the development of HUS among children with VTEC infections. Further studies are needed to determine their relative contribution to the pathophysiology of classic HUS.

Monocyte chemoattractant protein-1 and interleukin-8 levels in urine and serum of patents with hemolytic uremic syndrome

The epidemic form of the hemolytic uremic syndrome (HUS) in children is hallmarked by endothelial cell damage, most predominantly displayed by the glomerular capillaries. The influx of mononuclear (MO) and polymorphonuclear cells (PMNs) into the glomeruli may be an important event in the initiation, prolongation, and progression of glomerular endothelial cell damage in HUS patients. The molecular mechanisms for the recruitment of these leukocytes into the kidney are unclear, but monocyte chemoattractant protein-1 (MCP-1) and IL-8 are suggested to be prime candidates. In this study, we analyzed the presence of both chemokines in 24-h urinary (n = 15) and serum (n = 14) samples of HUS children by specific ELISAs. Furthermore, kidney biopsies of three different HUS children were examined for MO and PMN cell infiltration by histochemical techniques and electron microscopy. Whereas the chemokines MCP-1 and IL-8 were present in only very limited amounts in urine of 17 normal control subjects, serial samples of HUS patients demonstrated significantly elevated levels of both chemokines. HUS children with anuria showed higher initial and maximum chemokine levels than their counterparts without anuria. A strong positive correlation was observed between urinary MCP-1 and IL-8 levels. Whereas initial serum IL-8 levels were significantly increased in HUS children, serum MCP-1 levels were only slightly elevated compared with serum MCP-1 in control children. No correlation was found between urinary and serum chemokine concentrations. Histologic and EM studies of HUS biopsy specimens clearly showed the presence of MOs and to a lesser extent of PMNs in the glomeruli. The present data suggest an important local role for MOs and PMNs in the process of glomerular endothelial-cell damage. The chemokines MCP-1 and IL-8 may possibly be implicated in the pathogenesis of HUS through the recruitment and activation of MOs and PMNs, respectively.

Peripheral blood neutrophil responses in children with shigellosis

Alterations in peripheral blood neutrophil function are known to occur in patients with colitis and may have a role in precipitating nonspecific tissue injury. It is not known whether neutrophil function is altered in patients with Shigella dysenteriae type 1 infection, during which there is extensive colitis and which may be associated with life-threatening complications in young children. Three aspects of peripheral blood neutrophil function, polarization, attachment to yeast particles, and locomotion, were therefore studied in 111 children with S. dysenteriae type 1 infection and 57 children without any infection. All children were aged 12 to 60 months. Of the children with S. dysenteriae type 1 infection, 42 had leukemoid reaction, hemolytic-uremic syndrome, or septicemia (complicated shigellosis), while the others did not (uncomplicated shigellosis). Polarization and locomotion in the absence of chemoattractants and in response to N-formylmethionyl-leucylphenylalanine (FMLP) and the lipopolysaccharide (LPS) of S. dysenteriae type 1 were determined. Attachment to unopsonized and opsonized yeast particles was also determined. Children with shigellosis (uncomplicated or complicated) had more polarized neutrophils with and without chemoattractants than uninfected children (P < 0.05). Children with complicated shigellosis had more polarized neutrophils with FMLP at 10(-7) and 10(-6) M (P < 0.05) and with LPS than children with uncomplicated shigellosis (P < 0.05). At 3 to 5 days after enrollment, the numbers of polarized neutrophils with 10(-8), 10(-6), and 10(-5) M FMLP declined in children with uncomplicated shigellosis but not in those with complicated shigellosis. Attachment to yeast particles was similar in all three groups of children. Locomotion was inhibited by LPS in children with shigellosis (P < 0.05), whether it was uncomplicated or complicated, compared with locomotion in uninfected children. Finally, neutrophil polarization in uninfected children was negatively influenced by nutritional status. Thus, poorly nourished uninfected children had more polarized neutrophils with FMLP at 10(-9) M (P < = 0.02) and 10(-5) M (P = 0.043) than their better-nourished counterparts. In summary, altered neutrophil responses are associated with both uncomplicated and complicated shigellosis.

Oxidative damage of red blood cells in haemolytic uraemic syndrome

Changes in red blood cell (RBC) lipid peroxidation [measured by malonyl dialdehyde (MDA) concentration], glutathione (GSH) metabolism, antioxidant enzyme activities (catalase, superoxide dismutase, glutathione peroxidase) and haemoglobin (Hb) metabolites (metHb, carboxy Hb) were studied in six children with post-enteropathic (D+) haemolytic uraemic syndrome (HUS) and ten controls. The in vitro effect of hydrogen peroxide [acetylphenylhydrazine (APH) test] on GSH and Hb metabolism was also investigated. MDA levels were significantly higher and the antioxidant enzyme activities were lower in HUS patients than in the controls (P < 0.01). The oxidised glutathione concentration was significantly higher in the patients than in the control children (26.3 +/- 12.6 vs. 10.9 +/- 1.8 nmol/g Hb. Percentage values of carboxy Hb and metHb were also higher in HUS (P < 0.01). Incubation of RBC with APH induced a more pronounced decrease in the concentration of GSH (P < 0.001) and a significant increase (P < 0.01) in the level of metHb and carboxy Hb in the HUS patients. This suggests that there is reduced RBC GSH stability in HUS. Utilisation of GSH and antioxidant enzymes leads to increased Hb oxidation and haemolysis. The oxidative damage may have an important role in the pathogenesis of haemolytic anaemia in HUS.

Interleukin-8 and polymorphoneutrophil leucocyte activation in hemolytic uremic syndrome of childhood

Polymorphoneutrophil leucocytes (PMNLs) are implicated in the pathogenesis of diarrhea-associated hemolytic uremic syndrome (D+ HUS). We investigated mechanisms of PMNL involvement by measuring tumor necrosis factor alpha (TNF alpha) and the novel cytokine, interleukin-8 (IL-8), a potent activator of neutrophils, together with alpha 1- antitrypsin-complexed elastase (alpha 1-AT-E) as a marker of neutrophil degranulation, and anti-neutrophil cytoplasmic antibodies (ANCA). IL-8 was not detected in the 17 normal children, but was significantly elevated in 20 of 25 D+ HUS children (P less than 0.005), and in three of nine children with non-diarrhea-associated (D-) HUS. Sequential data showed that IL-8 peaked transiently in the circulation, reaching a maximum just before a more protracted burst of alpha 1-AT-E. The IL-8 levels correlated significantly with circulating alpha 1-AT-E concentrations (r = 0.50, P less than 0.05). In D+ HUS IL-8 levels also correlated with the PMNL count (r = 0.63, P less than 0.005), and the highest values were seen in those children who died in the acute phase of the disease. TNF alpha was raised in only 1 of 16 D+ HUS children and in no patients were ANCA detected. The data suggest that PMNLs in HUS are recruited by IL-8, that this cytokine plays a key role in the PMNL activation which occurs, and that agents which suppress this recruitment and activation might play a therapeutic role in this disorder.

Neutrophil activation in the haemolytic uraemic syndrome: free and complexed elastase in plasma

There is evidence of neutrophil involvement in the pathogenesis of the haemolytic uraemic syndrome (HUS), and neutrophil release products are thought to cause endothelial cell damage. Elastase is the major lysosomal proteinase liberated by activated neutrophils. In this study we measured both free and complexed elastase. No free elastase activity could be detected in the plasma of patients with diarrhoea-associated (D+) HUS using a specific substrate. However, there was a marked increase in alpha 1-antitrypsin (alpha 1-AT) complexed elastase as measured by a newly developed enzyme-linked immunosorbent assay not only in D+ HUS, but also in non-diarrhoea-associated (D-) HUS. This finding is independent of either a high polymorphonuclear leucocyte count or renal failure. This increase in bound elastase together with our sequential data which demonstrate raised alpha 1-AT complexed elastase levels early in the disease process further support the theory that neutrophil activation is one of the key events in the pathophysiology of this disorder.

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.

Further evidence of lipid peroxidation in post-enteropathic haemolytic-uraemic syndrome

Lipid peroxidation may play a role in the pathogenesis of the haemolytic-uraemic syndrome (HUS). Thirteen children with the post-enteropathic form of HUS were studied using conjugated diene lipids as markers of in vivo lipid peroxidation. Levels of total conjugated diene lipids and 9,11-linoleic acid, the principal conjugated diene in human plasma, were greater in the acute phase of this disorder than in controls. The ratio of plasma vitamin E to lipid was lower than that in children with other renal diseases, and the expected positive correlation between vitamin E and lipids did not hold for HUS patients. These data provide further evidence of lipid peroxidation in HUS and a disturbance in the metabolism of the principal lipid-bound anti-oxidant vitamin E.