Shiga toxin triggers endothelial and podocyte injury: the role of complement activation

A large outbreak of the hemolytic-uremic syndrome caused by Shiga-toxin-producing Escherichia coli O104:H4 occurred in Germany in May 2011. The source of infection was undetermined. We conducted a matched case-control study and a recipe-based restaurant cohort study, along with environmental, trace-back, and trace-forward investigations, to determine the source of infection. The case-control study included 26 case subjects with the hemolytic-uremic syndrome and 81 control subjects. The outbreak of illness was associated with sprout consumption in univariable analysis (matched odds ratio, 5.8; 95% confidence interval [CI], 1.2 to 29) and with sprout and cucumber consumption in multivariable analysis. Among case subjects, 25% reported having eaten sprouts, and 88% reported having eaten cucumbers. The recipe-based study among 10 groups of visitors to restaurant K included 152 persons, among whom bloody diarrhea or diarrhea confirmed to be associated with Shiga-toxin-producing E. coli developed in 31 (20%). Visitors who were served sprouts were significantly more likely to become ill (relative risk, 14.2; 95% CI, 2.6 to ∞). Sprout consumption explained 100% of cases. Trace-back investigation of sprouts from the distributor that supplied restaurant K led to producer A. All 41 case clusters with known trading connections could be explained by producer A. The outbreak strain could not be identified on seeds from the implicated lot. Our investigations identified sprouts as the most likely outbreak vehicle, underlining the need to take into account food items that may be overlooked during subjects' recall of consumption.

Haemolytic uraemic syndrome is a form of thrombotic microangiopathy affecting predominantly the kidney and characterised by a triad of thrombocytopenia, mechanical haemolytic anaemia, and acute kidney injury. The term encompasses several disorders: shiga toxin-induced and pneumococcus-induced haemolytic uraemic syndrome, haemolytic uraemic syndrome associated with complement dysregulation or mutation of diacylglycerol kinase ɛ, haemolytic uraemic syndrome related to cobalamin C defect, and haemolytic uraemic syndrome secondary to a heterogeneous group of causes (infections, drugs, cancer, and systemic diseases). In the past two decades, experimental, genetic, and clinical studies have helped to decipher the pathophysiology of these various forms of haemolytic uraemic syndrome and undoubtedly improved diagnostic approaches. Moreover, a specific mechanism-based treatment has been made available for patients affected by atypical haemolytic uraemic syndrome due to complement dysregulation. Such treatment is, however, still absent for several other disease types, including shiga toxin-induced haemolytic uraemic syndrome.

The hemolytic-uremic syndrome consists of the triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. The common form of the syndrome is triggered by infection with Shiga toxin-producing bacteria and has a favorable outcome. The less common form of the syndrome, called atypical hemolytic-uremic syndrome, accounts for about 10% of cases, and patients with this form of the syndrome have a poor prognosis. Approximately half of the patients with atypical hemolytic-uremic syndrome have mutations in genes that regulate the complement system. Genetic factors in the remaining cases are unknown. We studied the role of thrombomodulin, an endothelial glycoprotein with anticoagulant, antiinflammatory, and cytoprotective properties, in atypical hemolytic-uremic syndrome. We sequenced the entire thrombomodulin gene (THBD) in 152 patients with atypical hemolytic-uremic syndrome and in 380 controls. Using purified proteins and cell-expression systems, we investigated whether thrombomodulin regulates the complement system, and we characterized the mechanisms. We evaluated the effects of thrombomodulin missense mutations associated with atypical hemolytic-uremic syndrome on complement activation by expressing thrombomodulin variants in cultured cells. Of 152 patients with atypical hemolytic-uremic syndrome, 7 unrelated patients had six different heterozygous missense THBD mutations. In vitro, thrombomodulin binds to C3b and factor H (CFH) and negatively regulates complement by accelerating factor I-mediated inactivation of C3b in the presence of cofactors, CFH or C4b binding protein. By promoting activation of the plasma procarboxypeptidase B, thrombomodulin also accelerates the inactivation of anaphylatoxins C3a and C5a. Cultured cells expressing thrombomodulin variants associated with atypical hemolytic-uremic syndrome had diminished capacity to inactivate C3b and to activate procarboxypeptidase B and were thus less protected from activated complement. Mutations that impair the function of thrombomodulin occur in about 5% of patients with atypical hemolytic-uremic syndrome. 2009 Massachusetts Medical Society