Search

Author(s): Dineke Westra[sup.1] , Elena B. Volokhina[sup.1] , Renate G. van der Molen[sup.2] , Thea J. A. M. van der Velden[sup.1] , Annelies Jeronimus-Klaasen[sup.1] , Joop Goertz[sup.2] , Valentina Gracchi[sup.3] [...], Background The role of complement in the atypical form of hemolytic uremic syndrome (aHUS) has been investigated extensively in recent years. As the HUS-associated bacteria Shiga-toxin-producing Escherichia coli (STEC) can evade the complement system, we hypothesized that complement dysregulation is also important in infection-induced HUS. Methods Serological profiles (C3, FH, FI, AP activity, C3d, C3bBbP, C3b/c, TCC, [alpha]FH) and genetic profiles (CFH, CFI, CD46, CFB, C3) of the alternative complement pathway were prospectively determined in the acute and convalescent phase of disease in children newly diagnosed with STEC-HUS or aHUS. Serological profiles were compared with those of 90 age-matched controls. Results Thirty-seven patients were studied (26 STEC-HUS, 11 aHUS). In 39 % of them, including 28 % of STEC-HUS patients, we identified a genetic and/or acquired complement abnormality. In all patient groups, the levels of investigated alternative pathway (AP) activation markers were elevated in the acute phase and normalized in remission. The levels were significantly higher in aHUS than in STEC-HUS patients. Conclusions In both infection-induced HUS and aHUS patients, complement is activated in the acute phase of the disease but not during remission. The C3d/C3 ratio displayed the best discrepancy between acute and convalescent phase and between STEC-HUS and aHUS and might therefore be used as a biomarker in disease diagnosis and monitoring. The presence of aberrations in the alternative complement pathway in STEC-HUS patients was remarkable, as well.

Author(s): Kioa L. Wijnsma[sup.1] , Sheila A. M. van Bommel[sup.1] , Thea van der Velden[sup.2] , Elena Volokhina[sup.2] , Michiel F. Schreuder[sup.1] , Lambertus P. van den Heuvel[sup.1] [sup.2] [sup.3] [...], Background In the majority of pediatric patients, the hemolytic-uremic syndrome (HUS) is caused by an infection with Shiga toxin-producing Escherichia coli (STEC), mostly serotype O157. It is important to discriminate between HUS caused by STEC and complement-mediated HUS (atypical HUS) due to differences in treatment and outcome. As STEC and its toxins can only be detected in the patient&apos;s stool for a short period of time after disease onset, the infectious agent may go undetected using only fecal diagnostic tests. Serum antibodies to lipopolysaccharide (LPS) of STEC persist for several weeks and may therefore be of added value in the diagnosis of STEC. Methods All patients with clinical STEC-HUS who were treated at Radboud University Medical Center between 1990 and 2014 were included in this retrospective single-center study. Clinical and diagnostic microbiological data were collected. Immunoglobulin M (IgM) antibodies against LPS of STEC serotype O157 were detected by a serological assay (ELISA). Results Data from 65 patients weres available for analysis. Fecal diagnostic testing found evidence of an STEC infection in 34/63 patients (54 %). Serological evidence of STEC O157 was obtained in an additional 16 patients. This is an added value of 23 % (p < 0.0001) when the serological antibody assay is used in addition to standard fecal diagnostic tests to confirm the diagnosis STEC-HUS. This added value becomes especially apparent when the tests are performed more than 7 days after the initial manifestation of the gastrointestinal symptoms. Conclusions The serological anti-O157 LPS assay clearly makes a positive contribution when used in combination with standard fecal diagnostic tests to diagnose STEC-HUS and should be incorporated in clinical practice.

Acute renal failure hallmarks the pathogenesis of the epidemic form of hemolytic uremic syndrome (D+HUS), which is caused by E. coli strains that produce Shiga-like toxin (Stx). In this study, we investigated the influence of Stx-1 on nitric oxide (NO) production by human glomerular microvascular endothelial cells (GMVEC) and human mesangial cells. NO synthesis by human mesangial cells is in the micromolar range and that of GMVEC in the picomolar range. Stx-1 reduced NO production in non-stimulated GMVEC (5 nmol/l Stx-1 required) without inhibition of protein synthesis. In non-stimulated and TNFα-pretreated mesangial cells, NO production was reduced with a maximal reduction at 10 fmol/l shiga toxin. The cellular iNOS antigen content in mesangial cells was reduced in a concentration-dependent way (10 fmol/l-100 pmol/l), while partial inhibition of protein synthesis required 10 nmol/l Stx-1 in these cells. Our in vitro data suggest that Stx may reduce NO synthesis during the course of HUS development, contributing to the aggravation of the thrombotic microangiopathy and renal failure as observed in HUS. [ABSTRACT FROM AUTHOR]

The complement system is an important part of innate immunity. Complement activation leads to formation of convertase enzymes, switch of their specificity from C3 to C5 cleavage, and generation of lytic membrane attack complexes (C5b-9) on surfaces of pathogens. Most C5 cleavage occurs via the complement alternative pathway (AP). The regulator properdin promotes generation and stabilization of AP convertases. However, its role in C5 activation is not yet understood. In this work, we showed that serum properdin is essential for LPS- and zymosan-induced C5b-9 generation and C5b-9-mediated lysis of rabbit erythrocytes. Furthermore, we demonstrated its essential role in C5 cleavage by AP convertases. To this end, we developed a hemolytic assay in which AP convertases were generated on rabbit erythrocytes by using properdin-depleted serum in the presence of C5 inhibitor (step 1), followed by washing and addition of purified C5-C9 components to allow C5b-9 formation (step 2). In this assay, addition of purified properdin to properdin-depleted serum during convertase formation (step 1) was required to restore C5 cleavage and C5b-9-mediated hemolysis. Importantly, C5 convertase activity was also fully restored when properdin was added together with C5b-9 components (step 2), thus after convertase formation. Moreover, with C3-depleted serum, not capable of forming new convertases but containing properdin, in step 2 of the assay, again full C5b-9 formation was observed and blocked by addition of properdin inhibitor Salp20. Thus, properdin is essential for the convertase specificity switch toward C5, and this function is independent of properdin's role in new convertase formation., (Copyright © 2021 by The American Association of Immunologists, Inc.)