Hemolytic uremic syndrome (HUS) is commonly associated with Shiga toxin (Stx)-producing Escherichia coli O157:H7 infection. This study examined patient samples for complement activation on leukocyte-platelet complexes and microparticles as well as donor samples for Stx and lipopolysaccharide (O157LPS)-induced complement activation on platelet-leukocyte complexes and microparticles. Results, analyzed by flow cytometry, showed that whole blood from a child with HUS had surface-bound C3 on 30% of platelet-monocyte complexes compared to 14% after recovery and 12% in pediatric controls. Plasma samples from 12 HUS patients were analyzed for the presence of microparticles derived from platelets, monocytes and neutrophils. Acute phase samples exhibited high levels of platelet microparticles and, to a lesser extent, monocyte microparticles, both bearing C3 and C9. Levels decreased significantly at recovery. Stx or O157LPS incubated with donor whole blood increased the population of platelet-monocyte and platelet-neutrophil complexes with surface-bound C3 and C9, an effect enhanced by co-stimulation with Stx and O157LPS together. Both Stx and O157LPS induced the release of C3 and C9-bearing microparticles from platelets and monocytes. Released microparticles were phagocytosed by neutrophils. The presence of complement on platelet-leukocyte complexes, and microparticles derived from these cells, suggests a role in the inflammatory and thrombogenic events occurring during HUS.
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