Acute inflammation in the pathogenesis of hemolytic-uremic syndrome

Abstract

The patient, a 68-year-old white woman, presented to her primary physician with two to three days of bloody diarrhea; bilateral, crampy, lower abdominal pain, and fever to 101°F. Initially, she was treated with clear liquids as well as ciprofloxacin and loperamide. Over the next 24 hours, diarrhea, nausea, and vomiting increased, causing her to go to the emergency ward. Her family had noted progressive confusion over the previous 24 hours. There was no history of recent travel, nor was there any known contact with infected individuals. Her dietary history was significant for the ingestion of hamburger meat three days prior to the onset of symptoms. She had had type II diabetes mellitus for eight years, hypertension for 25 years, and hypothyroidism. Her medications on admission were hydrochlorothiazide, 25 mg/day; metoprolol, 25 mg twice daily; and thyroxine in addition to the ciprofloxacin and loperamide. There was no family history of renal or hematologic disease. A retired secretary who lived alone, she was too confused to give a review of systems, although her family stated that prior to this acute illness she had been doing well. Physical examination in the emergency ward revealed a markedly confused woman unable to state her name or the date. Her temperature was 38.6°C, her blood pressure was 140/80 mm Hg, and her heart rate was 86 beats/min. The head and neck examination were significant only for mildly icteric sclera. The lungs were clear to auscultation and percussion. The jugular veins were not distended, and no murmurs, rubs, or gallops were heard. Initial abdominal examination was notable for hypoactive bowel sounds, although the abdomen was soft and non-tender to palpation. Rectal examination revealed brown stool that was 4+ positive for occult blood and later found to be positive for fecal leukocytes. The neurologic examination was limited due to the confused state of the patient, but it did not reveal any focal defects. Laboratory testing revealed: serum sodium, 135 mEq/L; potassium, 3.4 mEq/L; chloride, 102 mEq/L; and bicarbonate, 19 mmol/L. The serum creatinine was 3.7 mg/dL; blood urea nitrogen, 110 mg/dL; and total bilirubin, 4.2 mg/dL with normal hepatic transaminases. Hematocrit was 25% with a hemoglobin of 8.1 g/dL. The leukocyte count was 29,700/mm3 with 86% polymorphonuclear cells, 3% bands, 8% lymphocytes, and 3% mononuclear cells. The platelet count was 49,000/mm3. Urinalysis revealed a specific gravity of 1.011; pH 5; 2+ protein, 2+ blood, and 5 to 7 red blood cells/high-power field in the sediment. No cellular casts were present. A chest radiograph was unremarkable, and a KUB radiograph revealed an ileus without evidence of free air. Over the following 12 hours, the patient's abdominal examination changed, with the development of overt peritoneal signs leading to an exploratory laparotomy. Extensive edema of the distal ileum and colon with evidence of infarction was found. A partial colectomy, partial ileal resection, and ileostomy were performed. Pathology of the colon revealed extensive bowel wall edema with regions of infarction, sloughing of mucosa, and local microangiopathy. The bowel had marked infiltration of polymorphonuclear cells with crypt abscesses. Her postoperative course was complicated by oliguria and rapidly worsening renal function. Hemodialysis was initiated. She was treated with broad-spectrum antibiotics and underwent a total of six plasma exchange treatments using fresh frozen plasma as the replacement fluid. A stool culture from her initial visit with her primary physician grew Escherichia coli O157:H7. Her hospital course was prolonged (4 months total) and complicated by adult respiratory distress syndrome (ARDS), pancreatitis, seizures, Clostridium difficile colitis, and Staphylococcus aureus bacteremia. She never regained renal function, but her mental status returned to normal. DR. ANDREW J. KING (Division Head, Division of Nephrology, Scripps Clinic and Green Hospital, La Jolla, California, USA): This unfortunate woman provides a dramatic illustration of the devastating nature of adult hemolytic-uremic syndrome (HUS) induced by enterohemorrhagic Escherichia coli (EHEC). She had multi-organ involvement, including the gut, central nervous system, and kidney, a presentation not too divergent from the patient with thrombotic microangiopathy first described by Eli Moschowitz in 19241.Moschowitz E. Hyaline thrombosis of the terminal arterioles and capillaries: A hitherto undescribed disease.Proc NY Pathol Soc. 1924; 29: 21-24Google Scholar. Thrombotic microangiopathy (TMA) is a term applied to a group of disorders that present with thrombocytopenia, evidence of red blood cell destruction, and a characteristic pathologic appearance in the microvasculature, including endothelial cell injury and platelet deposition. Thrombotic microangiopathy is associated with a wide range of infections, drugs, tumors, and other disorders. The focus of this report, however, is HUS triggered by EHEC. First described by Gasser et al in 19552.Gasser C. Gautier E. Steck A. et al.Hamolytisch-uramische Syndrome: bilaterale Nierenrindennekrosen bei akuten erwobenen hamolytischen anamien.Schweiz Med Wochenshr. 1955; 85: 905-909PubMed Google Scholar, HUS is a term applied to a TMA with predominant renal involvement. Although there had been speculation that HUS and thrombotic thrombocytopenic purpura (TTP) were differing manifestations of the same disease, it recently has become clear that for the majority of adults with TTP, the key pathologic feature is an immunoglobulin that inactivates circulating von Willebrand factor (vWF)-cleaving protease3.Furlan M. Robles R. Galbusera M. et al.von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome.N Engl J Med. 1998; 339: 1578-1584Crossref PubMed Scopus (1437) Google Scholar,4.Tsai H.M. Lian E.C. Antibodies to von Willebrand factor-cleaving protease in acute thrombotic thrombocytopenic purpura.N Engl J Med. 1998; 339: 1585-1594Crossref PubMed Scopus (1432) Google Scholar. Failure to properly metabolize naturally occurring ultralarge multimers of vWF leads to increased binding to platelet glycoproteins under conditions of high shear stress, that is, that which exists in the microvasculature. These features of TTP explain the remarkable efficacy of plasma exchange in this disorder5.Rock G.A. Shumak K.H. Buskard N.A. et al.Comparison of plasma exchange with plasma infusion in the treatment of thrombotic thrombocytopenic purpura.N Engl J Med. 1991; 325: 393-397Crossref PubMed Scopus (1464) Google Scholar. By contrast, vWF-cleaving protease activity is normal in patients with HUS, and the efficacy of plasma exchange is much less clear. Unlike TTP, patients with diarrhea-induced HUS have abundant evidence of an acute inflammatory response, the magnitude of which predicts clinical outcome. In this Forum, I will review evidence suggesting that inflammatory cells and their byproducts play a major role in (1) loss of intestinal barrier function, thereby promoting movement of endotoxin and Shiga toxins into the circulation; (2) delivery of Shiga toxins to target organs; (3) sensitization of target organs to Shiga toxins by increasing glycolipid receptor expression; and (4) direct injury of target organ endothelium. Although definitive evidence for a role of inflammatory cells and their mediators is lacking in humans, on circumstantial evidence, the case is compelling. Patients with HUS due to Shiga toxin-producing Escherichia coli (STEC) rarely present in the first 24 to 48 hours and thus, as with other forms of acute renal failure (ARF), we are left looking for the “smoking gun,” the mediators that cause the ARF. Shiga toxin (Stx)-producing Escherichia coli has been designated by the U.S. Centers for Disease Control and Prevention as an “emerging pathogen”6.Feng P. Escherichia coli serotype O157:H7 infection in humans.Emerg Infect Dis. 1995; 1: 47-52Crossref PubMed Scopus (131) Google Scholar. As many as 90% of children with HUS have antecedent STEC, typically of the serotype O157:H77.Siegler R.L. Pavia A.T. Christofferson R.D. Milligan M.K. A 20-year population-based study of postdiarrheal hemolytic uremic syndrome in Utah.Pediatrics. 1994; 94: 35-40PubMed Google Scholar. The association of Shiga toxin-producing Shigella dysenteriae with HUS was first made by Koster et al in 19788.Koster F. Levin J. Walker L. et al.Hemolytic-uremic syndrome after shigellosis. Relation to endotoxemia and circulating immune complexes.N Engl J Med. 1978; 298: 927-933Crossref PubMed Scopus (240) Google Scholar, followed by observations indicating an association of E. coli cytotoxins with the syndrome by Karmali et al in 19859.Karmali M.A. Petric M. Lim C. et al.The association between idiopathic hemolytic uremic syndrome and infection by verotoxin-producing Escherichia coli.J Infect Dis. 1985; 151: 775-782Crossref PubMed Scopus (1075) Google Scholar. The implicated E. coli cytotoxins, Stx1 and Stx2, belong to a family of bacterial protein toxins related to the parent Shiga toxin, which share the same enzymatic action and recognize related host-neutral glycolipid receptors. Interest in this disease has been fostered by considerable media attention stemming from several notable outbreaks, including one in 1993 related to undercooked hamburgers at “Jack in the Box” restaurants in the northwest United States and one more recently in Japan. Depending on the outbreak, patients with documented STEC have a risk of developing HUS of approximately 5% to 10%7.Siegler R.L. Pavia A.T. Christofferson R.D. Milligan M.K. A 20-year population-based study of postdiarrheal hemolytic uremic syndrome in Utah.Pediatrics. 1994; 94: 35-40PubMed Google Scholar. Details regarding the genetics, regulation, structure, enzymatic specificity, and physiology of the Stx family are found in several reviews10.Acheson D.W.K. Donohue-Rolfe A. Keusch G.T. The family of Shiga and Shiga-like toxins.Sourcebook of Bacterial Protein Toxins. edited by Alouf JE, Freer JH. Academic Press, London1991: 415-433Google Scholar, 11.Takeda T. Dohi S. 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Lopez E.L. et al.Susceptibility of hemolytic-uremic syndrome relates to erythrocyte glycosphingolipid patterns.J Infect Dis. 1993; 168: 476-479Crossref PubMed Scopus (37) Google Scholar. Upon binding, internalization and activation of the A subunit lead to depurination of a specific adenosine in 28S ribosomal RNA; the end result is irreversible inhibition of protein elongation14.Endo Y. Tsurugi K. Yutsudo T. Site of action of a Verotoxin (VT2) from Escherichia coli O157:H7 and of Shiga toxin on eukaryotic ribosomes.Eur J Biochem. 1988; 171: 45-50Crossref PubMed Scopus (602) Google Scholar. Glomerular endothelial cells and, to a greater extent, renal tubular epithelial cells, express Gb3, thereby contributing to the propensity of patients infected with STEC to develop acute renal failure. The woman presented today had high fever and marked leukocytosis, common findings in patients presenting with STEC. Leukocytosis can be extreme, as in leukemoid reactions, and it is a positive predictor of acute mortality and residual nephropathy15.Walters M.D. Matthel U. Jay R. et al.The polymorphonuclear count in childhood hemolytic uremic syndrome.Pediatr Nephrol. 1989; 3: 130-134Crossref PubMed Scopus (132) Google Scholar, 16.Coad N.A.G. Marshall T. Rowe B. Taylor C.M. Changes in the postenteropathic form of the hemolytic uremic syndrome in children.Clin Nephrol. 1991; 35: 10-16PubMed Google Scholar, 17.Milford D.V. Taylor C.M. Guttridge B. et al.Haemolytic uremic syndromes in the British Isles, 1985–8: Association with Verocytotoxin-producing Escherichia coli. Part 1: clinical and epidemiological aspects.Arch Dis Child. 1990; 65: 716-721Crossref PubMed Scopus (152) Google Scholar, 18.Fitzpatrick M.M. Shah V. Trompeter R.S. et al.Interleukin-8 and polymorphonuclear leukocyte activation in hemolytic uremic syndrome.Kidney Int. 1992; 42: 951-956Abstract Full Text PDF PubMed Scopus (127) Google Scholar. Children with “diarrhea-positive” HUS (D+HUS) have significantly higher leukocyte counts on presentation than do children with atypical “diarrhea-negative” HUS (D-HUS); this finding suggests that the intestinal disease is an important factor in generating the leukocytosis15.Walters M.D. Matthel U. Jay R. et al.The polymorphonuclear count in childhood hemolytic uremic syndrome.Pediatr Nephrol. 1989; 3: 130-134Crossref PubMed Scopus (132) Google Scholar. In the Osaka outbreak of 1996, both leukocyte count and C-reactive protein were higher in the group of children with STEC who developed HUS compared to infected children who did not19.Ikeda K. Ida O. Kimoto K. et al.Predictors for the development of haemolytic uraemic syndrome with Escherichia coli O157:H7 infections: With focus on the day of illness.Epidemiol Infect. 2000; 124: 343-349Crossref PubMed Scopus (26) Google Scholar. Severe gastrointestinal disease also portends a poor prognosis in children with STEC. The gastrointestinal disease in patients with STEC varies from watery diarrhea to the most severe form, hemorrhagic colitis. Colonic inflammation might play a role in local intestinal microangiopathy, the transfer of Stx from the bowel lumen through the lamina propria and into the circulation, and the generation of a systemic inflammatory response Figure 1. Although STEC was not previously thought to provoke marked intestinal inflammation, Slutsker et al noted that patients with STEC frequently have fecal leukocytes20.Slutsker L. Ries A.A. Greene K.D. et al.Escherichia coli O157:H7 diarrhea in the United States: clinical and epidemiologic factors.Ann Intern Med. 1997; 126: 505-513Crossref PubMed Scopus (234) Google Scholar. Indeed, colonic biopsy specimens from patients with STEC often have crypt abscesses and infiltrates of monocytes and polymorphonuclear cells (PMNs)21.Remis R. MacDonald K.L. Riley L.W. et al.Sporadic cases of hemorrhagic colitis associated with Escherichia coli O157:H7.Ann Intern Med. 1984; 101: 624-626Crossref PubMed Scopus (114) Google Scholar, 22.Kelly J. Oryshak A. Wenetsek M. The colonic pathological variability of infection by O157:H7 infection.Am J Surg Pathol. 1990; 14: 87-92Crossref PubMed Scopus (73) Google Scholar, 23.Hunt C.M. Harvey J.A. Youngs E.R. Reid T.M. Clinical and pathological variability of infection by enterohaemorrhagic (Verocytotoxin producing) Escherichia coli.J Clin Pathol. 1989; 42: 847-852Crossref PubMed Scopus (19) Google Scholar. In rabbits, infection with E. coli O157:H7 leads to severe inflammatory colitis with PMN infiltrates24.Zhe L. Bell C. Buret A. et al.The effect of enterohemorrhagic Escherichia coli O157:H7 on intestinal structure and solute transport in rabbits.Gastroenterology. 1993; 104: 467-474PubMed Google Scholar. In this model, infusion of monoclonal antibodies directed toward the PMN adhesion molecule CD-18 prevented intestinal infiltration of PMN and rendered histologic and functional protection25.Elliott E. Li Z. Bell C. et al.Modulation of host response to Escherichia coli O157:H7 infection by anti-CD18 antibody in rabbits.Gastroenterology. 1994; 106: 1554-1561PubMed Google Scholar. Shiga toxin traverses polarized intestinal human epithelial cells grown in tissue culture and retains biologic activity26.Hurley B.P. Jacewicz M. Thorpe C.M. et al.Shiga toxins 1 and 2 translocate differently across polarized intestinal epithelial cells.Infect Immun. 1999; 67: 6670-6677PubMed Google Scholar. Recent evidence suggests that Stx induces a chemokine response from human intestinal epithelial cells27.Thorpe C.M. Hurley B.P. Lincicome L.L. et al.Shiga toxins stimulate secretion of interleukin-8 from intestinal epithelial cells.Infect Immun. 1999; 67: 5985-5993PubMed Google Scholar. Using a human colonic epithelial cell line, Stx treatment led to “superinduction” of interleukin-8 (IL-8) with increase in both IL-8 mRNA and protein, the latter occurring despite the known inhibitory effects of Stx on protein elongation27.Thorpe C.M. Hurley B.P. Lincicome L.L. et al.Shiga toxins stimulate secretion of interleukin-8 from intestinal epithelial cells.Infect Immun. 1999; 67: 5985-5993PubMed Google Scholar. Secretion of IL-8 into the lamina propria might create a chemokine gradient sufficient to recruit circulating PMNs. Both IL-8 and tumor necrosis factor-α (TNF-α) are more elevated in stools of patients with Stx-producing S. dysenteriae compared to patients infected with non-Stx-producing S. flexneri28.Raqib R. Wretlind B. Anderson J. Lindberg A.A. Cytokine secretion in acute shigellosis is correlated to disease activity and directed more to stool than to plasma.J Infect Dis. 1995; 171: 376-384Crossref PubMed Scopus (92) Google Scholar. Several investigators have found that patients with STEC-induced HUS have elevated circulating levels and urinary excretion of IL-8 Table 1. The magnitude of IL-8 elevation correlates with markers of PMN degranulation and with patient outcome18.Fitzpatrick M.M. Shah V. Trompeter R.S. et al.Interleukin-8 and polymorphonuclear leukocyte activation in hemolytic uremic syndrome.Kidney Int. 1992; 42: 951-956Abstract Full Text PDF PubMed Scopus (127) Google Scholar. Other potential intestinal sources of chemokine production are the resident and influxing leukocytes in the lamina propria. Murine macrophages exposed to Stx increase production of both TNF-α and IL-639.Tesh V.L. Ramegowda B. Samuel J.E. Purified Shiga-toxins induce expression of proinflammatory cytokines from murine peritoneal macrophages.Infect Immun. 1994; 62: 5085-5094PubMed Google Scholar. Van Setten et al have shown in human monocytes that Stx increases production of IL-1β, TNF-α, IL-6, and IL-8 and does not inhibit protein synthesis40.Van Setten P.A. Monnens L.A. Verstraten R.G. et al.Effects of verocytotoxin-1 on nonadherent human monocytes: Binding characteristics, protein synthesis, and induction of cytokine release.Blood. 1997; 88: 174-183Google Scholar. Binding sites for Stx on the monocytes were increased with lipopolysaccharide exposure. By contrast, Ramegowda and Tesh found that human monocytes and monocytic cell lines were quite resistant to Stx unless the cells were pretreated with phorbol esters41.Ramegowda B. Tesh V. Differentiation-associated toxin receptor modulation, cytokine production and sensitivity to Shiga-like toxins in human monocytes and monocytic cell lines.Infect Immun. 1996; 64: 1173-1180Crossref PubMed Google Scholar.Table 1Blood and urinary cytokines in HUSCytokineLevelsReferencesIL-8BloodIncreased18.Fitzpatrick M.M. Shah V. Trompeter R.S. et al.Interleukin-8 and polymorphonuclear leukocyte activation in hemolytic uremic syndrome.Kidney Int. 1992; 42: 951-956Abstract Full Text PDF PubMed Scopus (127) Google Scholar, 29.Westerholt S. Hartung T. Tollens M. et al.Inflammatory and immunological parameters in children with haemolytic uremic syndrome (HUS) and gastroenteritis–pathophysiological and diagnostic clues.Cytokine. 2000; 12: 822-827https://doi.org/10.1006/cyto.1999.0624Crossref PubMed Scopus (30) Google Scholar, 30.Yamamoto T. Nagayama K. Satomura K. et al.Increased serum IL-10 and endothelin levels in hemolytic uremic syndrome caused by Escherichia coli O157.Nephron. 2000; 84: 326-332Crossref PubMed Scopus (29) Google Scholar, 31.Litalien C. Proulx F. Mariscalco M.M. et al.Circulating inflammatory cytokine levels in hemolytic uremic syndrome.Pediatr Nephrol. 1999; 13: 840-845https://doi.org/10.1007/s004670050712Crossref PubMed Scopus (52) Google Scholar, 32.Proulx F. Turgeon J.P. Litalien C. et al.Inflammatory mediators in Escherichia coli O157:H7 hemorrhagic colitis and hemolytic-uremic syndrome.Pediatr Infect Dis J. 1998; 17: 899-904https://doi.org/10.1097/00006454-199810000-00010Crossref PubMed Scopus (52) Google Scholar, 33.Van Setten P.A. van Hinsbergh V.W. van den Heuvel L.P. et al.Monocyte chemoattractant protein-1 and interleukin-8 levels in urine and serum of patients with hemolytic uremic syndrome.Pediatr Res. 1998; 43: 759-767Crossref PubMed Scopus (89) Google Scholar, 35.Inward C.D. Varagunam M. Adu D. et al.Cytokines in haemolytic uraemic syndrome associated with verocytotoxin-producing Escherichia coli infection.Arch Dis Child. 1997; 77: 145-147Crossref PubMed Scopus (66) Google ScholarUrineIncreased33.Van Setten P.A. van Hinsbergh V.W. van den Heuvel L.P. et al.Monocyte chemoattractant protein-1 and interleukin-8 levels in urine and serum of patients with hemolytic uremic syndrome.Pediatr Res. 1998; 43: 759-767Crossref PubMed Scopus (89) Google ScholarTNF-αBloodIncreased36.Lopez E.L. Contrini M.M. Devotos S. et al.Tumor necrosis factor concentrations in hemolytic uremic syndrome patients and children with bloody diarrhea in Argentina.Pediatr Infect Dis J. 1995; 14: 594-598Crossref PubMed Scopus (60) Google ScholarUnchanged or infrequent18.Fitzpatrick M.M. Shah V. Trompeter R.S. et al.Interleukin-8 and polymorphonuclear leukocyte activation in hemolytic uremic syndrome.Kidney Int. 1992; 42: 951-956Abstract Full Text PDF PubMed Scopus (127) Google Scholar, 34.Karpman D. Andreasson A. Thysell H. et al.Cytokines in childhood hemolytic uremic syndrome and thrombotic thrombocytopenic purpura.Pediatr Nephrol. 1995; 9: 694-699Crossref PubMed Scopus (110) Google Scholar, 35.Inward C.D. Varagunam M. Adu D. et al.Cytokines in haemolytic uraemic syndrome associated with verocytotoxin-producing Escherichia coli infection.Arch Dis Child. 1997; 77: 145-147Crossref PubMed Scopus (66) Google Scholar, 37.Van de Kar N.C. Sauerwein R.W. Demacker P.N. et al.Plasma cytokine levels in hemolytic uremic syndrome.Nephron. 1995; 71: 309-313Crossref PubMed Scopus (66) Google ScholarUrineNo or scant dataIL-βBloodIncreased35.Inward C.D. Varagunam M. Adu D. et al.Cytokines in haemolytic uraemic syndrome associated with verocytotoxin-producing Escherichia coli infection.Arch Dis Child. 1997; 77: 145-147Crossref PubMed Scopus (66) Google ScholarUnchanged or infrequent37.Van de Kar N.C. Sauerwein R.W. Demacker P.N. et al.Plasma cytokine levels in hemolytic uremic syndrome.Nephron. 1995; 71: 309-313Crossref PubMed Scopus (66) Google ScholarUrineNo or scant dataIL-6BloodIncreased30.Yamamoto T. Nagayama K. Satomura K. et al.Increased serum IL-10 and endothelin levels in hemolytic uremic syndrome caused by Escherichia coli O157.Nephron. 2000; 84: 326-332Crossref PubMed Scopus (29) Google Scholar, 31.Litalien C. Proulx F. Mariscalco M.M. et al.Circulating inflammatory cytokine levels in hemolytic uremic syndrome.Pediatr Nephrol. 1999; 13: 840-845https://doi.org/10.1007/s004670050712Crossref PubMed Scopus (52) Google Scholar, 32.Proulx F. Turgeon J.P. Litalien C. et al.Inflammatory mediators in Escherichia coli O157:H7 hemorrhagic colitis and hemolytic-uremic syndrome.Pediatr Infect Dis J. 1998; 17: 899-904https://doi.org/10.1097/00006454-199810000-00010Crossref PubMed Scopus (52) Google Scholar, 34.Karpman D. Andreasson A. Thysell H. et al.Cytokines in childhood hemolytic uremic syndrome and thrombotic thrombocytopenic purpura.Pediatr Nephrol. 1995; 9: 694-699Crossref PubMed Scopus (110) Google Scholar, 37.Van de Kar N.C. Sauerwein R.W. Demacker P.N. et al.Plasma cytokine levels in hemolytic uremic syndrome.Nephron. 1995; 71: 309-313Crossref PubMed Scopus (66) Google Scholar, 38.Martin A.A. Woolven B.L. Harris S.J. et al.Plasminogen activator inhibitor type-1 and interleukin-6 in haemolytic uraemic syndrome.J Paediatr Child Health. 2000; 36: 327-331https://doi.org/10.1046/j.1440-1754.2000.00532.xCrossref PubMed Scopus (9) Google ScholarUnchanged or infrequent35.Inward C.D. Varagunam M. Adu D. et al.Cytokines in haemolytic uraemic syndrome associated with verocytotoxin-producing Escherichia coli infection.Arch Dis Child. 1997; 77: 145-147Crossref PubMed Scopus (66) Google ScholarUrineIncreased34.Karpman D. Andreasson A. Thysell H. et al.Cytokines in childhood hemolytic uremic syndrome and thrombotic thrombocytopenic purpura.Pediatr Nephrol. 1995; 9: 694-699Crossref PubMed Scopus (110) Google ScholarIL-10BloodIncreased30.Yamamoto T. Nagayama K. Satomura K. et al.Increased serum IL-10 and endothelin levels in hemolytic uremic syndrome caused by Escherichia coli O157.Nephron. 2000; 84: 326-332Crossref PubMed Scopus (29) Google Scholar, 31.Litalien C. Proulx F. Mariscalco M.M. et al.Circulating inflammatory cytokine levels in hemolytic uremic syndrome.Pediatr Nephrol. 1999; 13: 840-845https://doi.org/10.1007/s004670050712Crossref PubMed Scopus (52) Google Scholar, 32.Proulx F. Turgeon J.P. Litalien C. et al.Inflammatory mediators in Escherichia coli O157:H7 hemorrhagic colitis and hemolytic-uremic syndrome.Pediatr Infect Dis J. 1998; 17: 899-904https://doi.org/10.1097/00006454-199810000-00010Crossref PubMed Scopus (52) Google ScholarDecreased29.Westerholt S. Hartung T. Tollens M. et al.Inflammatory and immunological parameters in children with haemolytic uremic syndrome (HUS) and gastroenteritis–pathophysiological and diagnostic clues.Cytokine. 2000; 12: 822-827https://doi.org/10.1006/cyto.1999.0624Crossref PubMed Scopus (30) Google ScholarUrineNo or scant data Open table in a new tab Several potential consequences of a local inflammatory response in the lamina propria exist. Transepithelial migration of PMNs can lead to transient loss of colonic barrier function and cause the passage of luminal contents into the circulation42.Nash S. Stafford J. Madara J.L. Effects of polymorphonuclear leukocyte transmigration on the barrier function of the cultured intestinal epithelial monolayers.J Clin Invest. 1987; 80: 1104-1113Crossref PubMed Scopus (201) Google Scholar,43.Parsons P.E. Sugahara K. Cott G.R. et al.The effect of neutrophil migration and prolonged neutrophil contact on epithelial permeability.Am J Pathol. 1987; 129: 302-312PubMed Google Scholar. In one recent study, movement of PMNs from the basolateral to the apical side of a human intestinal epithelial cell line allows increasing translocation of both Stx1 and Stx2 in the opposite direction44.Hurley B.P. Thorpe C. Acheson D.W.K. Neutrophil translocation across intestinal epithelial cells is enhanced by neutrophil transmigration.Infect Immun. 2001; 69: 6148-6155Crossref PubMed Scopus (133) Google Scholar. Loss of barrier function could contribute to direct entry of Stx into the circulation, as well as endotoxemia that would promote a systemic cytokine response. To date, no one has been able to detect circulating Stx in patients with STEC. Recent studies, however, have revealed Stx bound to circulating PMNs in patients with D+HUS, thus confirming entry into the circulation45.Te Loo D.M. Hinsbergh V.W. Heuvel L.P. Monnens L.A. Detection of verocytotoxin bound to circulating polymorphonuclear leukocytes of patients with hemolytic uremic syndrome.J Am Soc Nephrol. 2001; 12: 800-806PubMed Google Scholar. Most cellular responses in vitro, however, are elicited at Stx doses well below the lower limits of detection in plasma. Sepsis syndrome is very uncommon in children with STEC, except in the setting of bowel infarction. In this regard, several investigators have found specific antibodies to the lipopolysaccharide of Stx-producing E. coli46.Chart H. Scotland S.M. Smith H.R. Rowe B. Antibodies to Escherichia coli O157 in patients with haemorrhagic colitis and haemolytic uraemic syndrome.J Clin Pathol. 1989; 42: 973-976Crossref PubMed Scopus (31) Google Scholar, 47.Bitzan M. Moebius E. Ludwig K. et al.High incidence of serum antibodies to Escherichia coli O157 lipopolysaccharide in children with hemolytic-uremic syndrome.J Pediatr. 1991; 119: 380-385Abstract Full Text PDF PubMed Scopus (119) Google Scholar, 48.Caprioli A. Luzzi I. Rosmini F. et al.Hemolytic-uremic syndrome and Vero cytotoxin-producing Escherichia coli infection in Italy. The HUS Italian Study Group.J Infect Dis. 1992; 166: 154-158Crossref PubMed Scopus (115) Google Scholar. Endotoxemia is much more prominent in patients with S. dysenteriae, an infection that is more likely to cause HUS and which is associated with high circulating levels of IL-1 and TNF-α. Increases in circulating inflammatory cytokines likely are triggered by the colonic infection and possibly by the low-grade endotoxemia Table 1. When assessing the degree of cytokine elevation, note that renal failure independently contributes to high levels49.Pereira B.J.G. Shapiro L. King A.J. et al.Plasma levels of IL-1α and TNFα and their specific inhibitors in undialyzed chronic renal failure, CAPD and hemodialysis patients.Kidney Int. 1994; 45: 8490-8896Abstract Full Text PDF Scopus (350) Google Scholar. Futhermore, patients with uncomplicated STEC also have increased levels. Despite these caveats, it appears that patients with HUS have elevated circulating inflammatory cytokines. I will discuss the role of these cytokines as possible “co-conspirators” in vascular injury in a few moments. However, local production of cytokines in the gut wall might be an importan