Portal de Periódicos da CAPES

Extracellular Vesicles and Renal Endothelial Cells

2021; Elsevier BV; Volume: 191; Issue: 5 Linguagem: Inglês

10.1016/j.ajpath.2021.02.011

1525-2191

Elisa Varrone, Domenica Carnicelli, Maurizio Brigotti,

Energy and Environment Impacts

This review focuses on typical hemolytic uremic syndrome (HUS), a life-threatening sequela of human infections caused, particularly in children, by Shiga toxin–producing Escherichia coli strains. Thrombotic microangiopathy of the brain and the kidney is the end point of toxin action, resulting in the hallmarks of HUS (ie, thrombocytopenia, anemia, and acute renal failure). A growing body of evidence points to the role of extracellular vesicles released in the blood of patients by toxin-challenged circulating cells (monocytes, neutrophils, and erythrocytes) and platelets, as a key factor in the pathogenesis of HUS. This review provides i) an updated description of the pathogenesis of Shiga toxin–producing E. coli infections; ii) an analysis of blood cell–derived extracellular vesicles, and of their parent cells, as triggering factors in HUS; and iii) a model explaining why Shiga toxin–containing vesicles dock preferentially to the endothelia of target organs. This review focuses on typical hemolytic uremic syndrome (HUS), a life-threatening sequela of human infections caused, particularly in children, by Shiga toxin–producing Escherichia coli strains. Thrombotic microangiopathy of the brain and the kidney is the end point of toxin action, resulting in the hallmarks of HUS (ie, thrombocytopenia, anemia, and acute renal failure). A growing body of evidence points to the role of extracellular vesicles released in the blood of patients by toxin-challenged circulating cells (monocytes, neutrophils, and erythrocytes) and platelets, as a key factor in the pathogenesis of HUS. This review provides i) an updated description of the pathogenesis of Shiga toxin–producing E. coli infections; ii) an analysis of blood cell–derived extracellular vesicles, and of their parent cells, as triggering factors in HUS; and iii) a model explaining why Shiga toxin–containing vesicles dock preferentially to the endothelia of target organs. The study of the pathogenesis of a given disease outlines the triggering factors and describes the chain of events involved in the development of the pathologic condition. In the case of infectious diseases, the identification of the microbial pathogenic factors and of the resulting host-pathogen interactions clarifies the mechanisms underlying the pathogenetic process. In many cases, however, a particular disease is the consequence of the complex interactions of several virulence factors, whereby the illness may not occur if one of these factors is removed or if their interplay is impaired. This review focuses on typical hemolytic uremic syndrome (HUS), a life-threatening condition caused by pathogenic bacteria known as Shiga toxin–producing Escherichia coli (STEC), which release potent exotoxin, named Shiga toxins (Stx).1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar The syndrome is the leading cause of acute renal failure in children aged <3 years, being characterized also by microangiopathic anemia and thrombocytopenia.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar HUS can occur in sporadic form, as microepidemics, or as community-wide foodborne outbreaks, as dramatically exemplified in recent years worldwide.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar HUS is a severe sequela of STEC infections occurring after a prodromal intestinal phase, characterized by watery and bloody diarrhea.2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar STEC are complex pathogens capable of tight and intimate interactions with the gut mucosa, culminating in the derangement of the absorption properties of the enterocytes (watery diarrhea).3Stevens M.P. Frankel G.M. The locus of enterocyte effacement and associated virulence factors of enterohemorrhagic Escherichia coli.Microbiol Spectr. 2014; 2 (EHEC-0007-2013)Crossref PubMed Scopus (68) Google Scholar These Stx-independent injuries, known as attaching and effacing lesions, are critical for the subsequent pathogenetic steps, such as the synthesis and release of Stx, which cross the intestinal mucosa to reach the lamina propria.2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar,3Stevens M.P. Frankel G.M. The locus of enterocyte effacement and associated virulence factors of enterohemorrhagic Escherichia coli.Microbiol Spectr. 2014; 2 (EHEC-0007-2013)Crossref PubMed Scopus (68) Google Scholar Bloody diarrhea is the consequence of toxin actions on the endothelial lining of the intestine, culminating in typical histopathologic changes, such as mucosal and submucosal edema, hemorrhage, focal necrosis, and thrombotic microangiopathy.4Bielaszewska M. Karch H. Consequences of enterohaemorrhagic Escherichia coli infection for the vascular endothelium.Thromb Haemost. 2005; 94: 312-318PubMed Google Scholar,5Richardson S.E. Karmali M.A. Becker L.E. Smith C.R. The histopathology of the hemolytic uremic syndrome associated with verocytotoxin-producing Escherichia coli infections.Hum Pathol. 1988; 19: 1102-1108Crossref PubMed Scopus (267) Google Scholar Lesions to the microvasculature of the gut trigger bloody diarrhea during precocious toxemia, whereas HUS develops 5 to 7 days later when the endothelial cells of the kidney and brain are targeted by the toxin.2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar Endothelial damage/dysfunction related to Stx action causing thrombotic microangiopathic lesions in target organs is considered the major pathogenetic event in HUS and occurs when Stx cross the epithelial lining of the large bowel and are transported in circulation. These injuries narrow renal glomerular capillaries, thereby damaging passing erythrocytes, and consume platelets; therefore, acute renal failure, thrombocytopenia, and anemia ensue.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar The latter condition is exacerbated by the specific targeting of red cell precursor by Stx1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar and by complement-mediated Stx-triggered hemolysis of mature erythrocytes.6Arvidsson I. Stahl A.L. Hedstrom M.M. Kristoffersson A.C. Rylander C. Westman J.S. Storry J.R. Olsson M.L. Karpman D. Shiga toxin-induced complement-mediated hemolysis and release of complement-coated red blood cell-derived microvesicles in hemolytic uremic syndrome.J Immunol. 2015; 194: 2309-2318Crossref PubMed Scopus (58) Google Scholar Stx are a family of AB5 bacterial toxins consisting of two main types (Stx1 and Stx2) and many different subtypes (4 for Stx1 and 12 for Stx2).1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,7Menge C. Molecular biology of Escherichia coli Shiga toxins' effects on mammalian cells.Toxins (Basel). 2020; 12: 345Crossref Scopus (23) Google Scholar,8Koutsoumanis K. Allende A. Alvarez-Ordonez A. Bover-Cid S. Chemaly M. Davies R. De Cesare A. Herman L. Hilbert F. Lindqvist R. Nauta M. Peixe L. Ru G. Simmons M. Skandamis P. Suffredini E. Jenkins C. Pires S.M. Morabito S. Niskanen T. Scheutz F. da Silva Felıcio M.T. Messens W. Bolton D. Pathogenicity assessment of Shiga toxin-producing Escherichia coli (STEC) and the public health risk posed by contamination of food with STEC.EFSA J. 2020; 18: e05967Google Scholar Only a few of these have been found in STEC isolates associated with severe human illness [eg, Stx1a (bloody diarrhea and rarely HUS) or Stx2a, mucus-activatable Stx2d, and the controversial Stx2c (bloody diarrhea and HUS)].8Koutsoumanis K. Allende A. Alvarez-Ordonez A. Bover-Cid S. Chemaly M. Davies R. De Cesare A. Herman L. Hilbert F. Lindqvist R. Nauta M. Peixe L. Ru G. Simmons M. Skandamis P. Suffredini E. Jenkins C. Pires S.M. Morabito S. Niskanen T. Scheutz F. da Silva Felıcio M.T. Messens W. Bolton D. Pathogenicity assessment of Shiga toxin-producing Escherichia coli (STEC) and the public health risk posed by contamination of food with STEC.EFSA J. 2020; 18: e05967Google Scholar Stx2a is mainly involved in HUS because the STEC strains that produce and release this subtype are epidemiologically associated with HUS.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,9Friedrich A.W. Bielaszewska M. Zhang W.L. Pulz M. Kuczius T. Ammon A. Karch H. Escherichia coli harboring Shiga toxin 2 gene variants: frequency and association with clinical symptoms.J Infect Dis. 2002; 185: 74-84Crossref PubMed Scopus (606) Google Scholar Stx are rarely found free in the bloodstream of patients during HUS10Brigotti M. Caprioli A. Tozzi A.E. Tazzari P.L. Ricci F. Conte R. Carnicelli D. Procaccino M.A. Minelli F. Ferretti A.V. Paglialonga F. Edefonti A. Rizzoni G. Shiga toxins present in the gut and in the polymorphonuclear leukocytes circulating in the blood of children with hemolytic-uremic syndrome.J Clin Microbiol. 2006; 44: 313-317Crossref PubMed Scopus (46) Google Scholar, 11Brigotti M. Tazzari P.L. Ravanelli E. Carnicelli D. Rocchi L. Arfilli V. Scavia G. Minelli F. Ricci F. Pagliaro P. Ferretti A.V. Pecoraro C. Paglialonga F. Edefonti A. Procaccino M.A. Tozzi A.E. Caprioli A. 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Serum Shiga toxin 2 values in patients during acute phase of diarrhoea-associated haemolytic uraemic syndrome.Acta Paediatr. 2015; 104: e564-e568Crossref PubMed Scopus (16) Google Scholar; rather, they are found free in blood during late toxemia and before the onset of HUS, as well as associated with circulating cells (neutrophils, monocytes, and erythrocytes) and platelets.10Brigotti M. Caprioli A. Tozzi A.E. Tazzari P.L. Ricci F. Conte R. Carnicelli D. Procaccino M.A. Minelli F. Ferretti A.V. Paglialonga F. Edefonti A. Rizzoni G. Shiga toxins present in the gut and in the polymorphonuclear leukocytes circulating in the blood of children with hemolytic-uremic syndrome.J Clin Microbiol. 2006; 44: 313-317Crossref PubMed Scopus (46) Google Scholar,11Brigotti M. Tazzari P.L. Ravanelli E. Carnicelli D. Rocchi L. Arfilli V. Scavia G. Minelli F. Ricci F. Pagliaro P. Ferretti A.V. Pecoraro C. Paglialonga F. Edefonti A. Procaccino M.A. Tozzi A.E. Caprioli A. Clinical relevance of Shiga toxin concentrations in the blood of patients with hemolytic uremic syndrome.Pediatr Infect Dis J. 2011; 30: 486-490Crossref PubMed Scopus (58) Google Scholar,15Arfilli V. Carnicelli D. Ardissino G. Torresani E. Scavia G. Brigotti M. A rapid and sensitive method to measure the functional activity of Shiga toxins in human serum.Toxins (Basel). 2015; 7: 4564-4576Crossref PubMed Scopus (11) Google Scholar, 16Stahl A.L. Sartz L. Nelsson A. Bekassy Z.D. Karpman D. Shiga toxin and lipopolysaccharide induce platelet-leukocyte aggregates and tissue factor release, a thrombotic mechanism in hemolytic uremic syndrome.PLoS One. 2009; 4: e6990Crossref PubMed Scopus (100) Google Scholar, 17Te Loo D.M. van Hinsbergh V.W. van den 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: 800-806Crossref PubMed Google Scholar, 18Brigotti M. He X. Carnicelli D. 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Platelet activation by Shiga toxin and circulatory factors as a pathogenetic mechanism in the hemolytic uremic syndrome.Blood. 2001; 97: 3100-3108Crossref PubMed Scopus (114) Google Scholar, 22van Setten P.A. Monnens L.A. Verstraten R.G. van den Heuvel L.P. van Hinsbergh V.W. Effects of verocytotoxin-1 on nonadherent human monocytes: binding characteristics, protein synthesis, and induction of cytokine release.Blood. 1996; 88: 174-183Crossref PubMed Google Scholar The release of extracellular vesicles containing Stx (and other virulence factors) by these stimulated cells is considered the trigger producing the transition from bloody diarrhea to life-threatening HUS.23Karpman D. Stahl A.L. Arvidsson I. Extracellular vesicles in renal disease.Nat Rev Nephrol. 2017; 13: 545-562Crossref PubMed Scopus (157) Google Scholar, 24Stahl A.L. Arvidsson I. Johansson K.E. Chromek M. Rebetz J. Loos S. Kristoffersson A.C. Bekassy Z.D. Morgelin M. Karpman D. A novel mechanism of bacterial toxin transfer within host blood cell-derived microvesicles.PLoS Pathog. 2015; 11: e1004619Crossref PubMed Scopus (76) Google Scholar, 25Stahl A.L. Sartz L. Karpman D. Complement activation on platelet-leukocyte complexes and microparticles in enterohemorrhagic Escherichia coli-induced hemolytic uremic syndrome.Blood. 2011; 117: 5503-5513Crossref PubMed Scopus (148) Google Scholar Stx activate the innate immune responses, resulting in immunopathologic changes related to inflammation and complement activation.26Lee M.S. Tesh V.L. Roles of Shiga toxins in immunopathology.Toxins (Basel). 2019; 11: 212Crossref Scopus (39) Google Scholar The multiple interactions of Stx with circulating cells, and with target epithelial and endothelial cells, induce the release of proinflammatory cytokines and chemokines capable of up-regulating the expression of specific toxin receptors (see the next paragraph), of exacerbating tissue damage in targeted organs, and of recruiting inflammatory cells in injured tissues.26Lee M.S. Tesh V.L. Roles of Shiga toxins in immunopathology.Toxins (Basel). 2019; 11: 212Crossref Scopus (39) Google Scholar Moreover, the activation of the alternative pathway of the complement system by Stx, as part of the innate immune response, is considered a crucial point in the development of renal injuries.26Lee M.S. Tesh V.L. Roles of Shiga toxins in immunopathology.Toxins (Basel). 2019; 11: 212Crossref Scopus (39) Google Scholar,27Orth D. Khan A.B. Naim A. Grif K. Brockmeyer J. Karch H. Joannidis M. Clark S.J. Day A.J. Fidanzi S. Stoiber H. Dierich M.P. Zimmerhackl L.B. Wurzner R. Shiga toxin activates complement and binds factor H: evidence for an active role of complement in hemolytic uremic syndrome.J Immunol. 2009; 182: 6394-6400Crossref PubMed Scopus (165) Google Scholar Stx are bipartite exotoxins composed of a single A chain, which is endowed with the enzymatic activity, noncovalently bound to five B chains forming a pentameric ring that surrounds the COOH-terminus of the A subunit.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,7Menge C. Molecular biology of Escherichia coli Shiga toxins' effects on mammalian cells.Toxins (Basel). 2020; 12: 345Crossref Scopus (23) Google Scholar The latter is a proenzyme that is enzymatically cleaved into two fragments (A1 and A2) linked by a disulfide bond that is reduced within cells, permitting the A1 fragment to express its deadenylating activity on 28S rRNA in ribosomes and on DNA in chromatin, leading to irreversible arrest of translation and to formation of nuclear apurinic sites, respectively.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,7Menge C. Molecular biology of Escherichia coli Shiga toxins' effects on mammalian cells.Toxins (Basel). 2020; 12: 345Crossref Scopus (23) Google Scholar Cleavage can occur during retrograde internalization in target cells by the protease furin or can be induced by extracellular or bacterial proteases.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,7Menge C. Molecular biology of Escherichia coli Shiga toxins' effects on mammalian cells.Toxins (Basel). 2020; 12: 345Crossref Scopus (23) Google Scholar It has been recently shown that cleaved unreduced Stx have changed their blood binding properties with respect to whole toxins.28Brigotti M. Orth-Holler D. Carnicelli D. Porcellini E. Galassi E. Tazzari P.L. Ricci F. Manoli F. Manet I. Talasz H. Lindner H.H. Speth C. Erbeznik T. Fuchs S. Posch W. Chatterjee S. Wurzner R. The structure of the Shiga toxin 2a A-subunit dictates the interactions of the toxin with blood components.Cell Microbiol. 2019; 21: e13000Crossref PubMed Scopus (10) Google Scholar Stx-intoxicated endothelial cells not only have impaired translation, but also activate a wide array of responses to injury, which have a great impact in the pathogenesis of HUS (eg, release of proinflammatory cytokines,29Jandhyala D.M. Thorpe C.M. Magun B. Ricin and Shiga toxins: effects on host cell signal transduction.Curr Top Microbiol Immunol. 2012; 357: 41-65PubMed Google Scholar up-regulation of adhesion molecules,30Zoja C. Buelli S. Morigi M. Shiga toxin-associated hemolytic uremic syndrome: pathophysiology of endothelial dysfunction.Pediatr Nephrol. 2010; 25: 2231-2240Crossref PubMed Scopus (145) Google Scholar and activation of the apoptotic program).31Tesh V.L. The induction of apoptosis by Shiga toxins and ricin.Curr Top Microbiol Immunol. 2012; 357: 137-178Crossref PubMed Scopus (75) Google Scholar Receptor-dependent toxicity is a key concept explaining why these powerful toxins cause damages to selected tissues in animals and humans. The B pentamers of the human subtypes Stx1a and Stx2a show a specific and preferential binding to globotriaosylceramide (Gb3Cer), a member of globoseries glycosphingolipids.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,32Muthing J. Schweppe C.H. Karch H. Friedrich A.W. Shiga toxins, glycosphingolipid diversity, and endothelial cell injury.Thromb Haemost. 2009; 101: 252-264Crossref PubMed Scopus (108) Google Scholar The same subtypes also interact, although weakly, with globotetraosylceramide.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,32Muthing J. Schweppe C.H. Karch H. Friedrich A.W. Shiga toxins, glycosphingolipid diversity, and endothelial cell injury.Thromb Haemost. 2009; 101: 252-264Crossref PubMed Scopus (108) Google Scholar On the other hand globotetraosylceramide is preferred by the Stx2e subtype associated with edema disease in pigs, that is capable of binding to Gb3Cer, globopentaosylceramide, and Forssman antigen.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar Therefore, the tissue expression of these glycolipids and their relative amounts might affect the sensitivity of cells to specific Stx subtypes. In humans, during HUS, several organs can be involved, with kidney and brain being predominantly targeted.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,2Tarr P.I. Gordon C.A. Chandler W.L. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome.Lancet. 2005; 365: 1073-1086Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar,4Bielaszewska M. Karch H. Consequences of enterohaemorrhagic Escherichia coli infection for the vascular endothelium.Thromb Haemost. 2005; 94: 312-318PubMed Google Scholar The focused expression of Gb3Cer by intestinal, renal, and cerebral endothelial cells and by other cells in the kidney (mesangial cells and tubular and glomerular epithelial cells) allows the toxin to target these organs preferentially by means of multivalent interactions of the glycolipid receptors with B subunits.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,32Muthing J. Schweppe C.H. Karch H. Friedrich A.W. Shiga toxins, glycosphingolipid diversity, and endothelial cell injury.Thromb Haemost. 2009; 101: 252-264Crossref PubMed Scopus (108) Google Scholar This is a crucial point to be considered because any hypothesis on the pathogenesis of HUS must explain the focused action of Stx on target cells expressing Gb3Cer.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar Besides Gb3Cer-expressing target cells, circulating erythrocytes, monocytes, and platelets also express this receptor with similar lipoforms.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,33Brigotti M. The interactions of human neutrophils with Shiga toxins and related plant toxins: danger or safety?.Toxins (Basel). 2012; 4: 157-190Crossref PubMed Scopus (25) Google Scholar Human neutrophils are peculiar in this respect because they specifically bind Stx even though they lack the set of enzymes necessary for the synthesis of these neutral glycolipids.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,34Macher B.A. Klock J.C. Isolation and chemical characterization of neutral glycosphingolipids of human neutrophils.J Biol Chem. 1980; 255: 2092-2096Abstract Full Text PDF PubMed Google Scholar In fact, they are not targeted by Stx; rather, they recognize these bacterial toxins through toll-like receptor 4 (TLR4).35Brigotti M. Carnicelli D. Arfilli V. Tamassia N. Borsetti F. Fabbri E. Tazzari P.L. Ricci F. Pagliaro P. Spisni E. Cassatella M.A. Identification of TLR4 as the receptor that recognizes Shiga toxins in human neutrophils.J Immunol. 2013; 191: 4748-4758Crossref PubMed Scopus (67) Google Scholar Interestingly, TLR4 interacts with Stx A chain rather than with the B chains.36Arfilli V. Carnicelli D. Rocchi L. Ricci F. Pagliaro P. Tazzari P.L. Brigotti M. Shiga toxin 1 and ricin A chain bind to human polymorphonuclear leucocytes through a common receptor.Biochem J. 2010; 432: 173-180Crossref PubMed Scopus (29) Google Scholar Moreover, in humans, the receptor pattern of circulating cells is complicated by the simultaneous expression of Gb3Cer and TLR4 by monocytes and platelets.1Detzner J. Pohlentz G. Muthing J. Valid presumption of Shiga toxin-mediated damage of developing erythrocytes in EHEC-associated hemolytic uremic syndrome.Toxins (Basel). 2020; 12: 373Crossref Scopus (5) Google Scholar,33Brigotti M. The interactions of human neutrophils with Shiga toxins and related plant toxins: danger or safety?.Toxins (Basel). 2012; 4: 157-190Crossref PubMed Scopus (25) Google Scholar A negative modulator of Stx2, known as human serum amyloid P (HuSAP) component, present in humans,37Armstrong G.D. Mulvey G.L. Marcato P. Griener T.P. Kahan M.C. Tennent G.A. Sabin C.A. Chart H. Pepys M.B. Human serum amyloid P component protects against Escherichia coli O157:H7 Shiga toxin 2 in vivo: therapeutic implications for hemolytic-uremic syndrome.J Infect Dis. 2006; 193: 1120-1124Crossref PubMed Scopus (37) Google Scholar,38Kimura T. Tani S. Matsumoto Yi Y. Takeda T. Serum amyloid P component is the Shiga toxin 2-neutralizing factor in human blood.J Biol Chem. 2001; 276: 41576-41579Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar binds tightly to this toxin type38Kimura T. Tani S. Matsumoto Yi Y. Takeda T. Serum amyloid P component is the Shiga toxin 2-neutralizing factor in human blood.J Biol Chem. 2001; 276: 41576-41579Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar,39Marcato P. Vander Helm K. Mulvey G.L. Armstrong G.D. Serum amyloid P component binding to Shiga toxin 2 requires both a subunit and B pentamer.Infect Immun. 2003; 71: 6075-6078Crossref PubMed Scopus (22) Google Scholar and impairs the Gb3Cer-related cytotoxic activity.39Marcato P. Vander Helm K. Mulvey G.L. Armstrong G.D. Serum amyloid P component binding to Shiga toxin 2 requires both a subunit and B pentamer.Infect Immun. 2003; 71: 6075-6078Crossref PubMed Scopus (22) Google Scholar On the other hand, HuSAP fails to inhibit and rather stimulates Stx2 binding to TLR4-expressing human polymorphonuclear leukocytes.40Griener T.P. Mulvey G.L. Marcato P. Armstrong G.D. 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