The Antibiotic Polymyxin B Impairs the Interactions between Shiga Toxins and Human Neutrophils.

Hemolytic uremic syndrome (HUS) is the life-threatenig sequela of intestinal infections by Shiga toxin (Stx)-producing Escherichia coli (STEC) in children. Human neutrophils specifically bind Stx through TLR4, the receptor of LPS. The binding could be considered protective (Stx sequestration) or harmful (toxin delivery to target organs). The amount of Stx on neutrophils is in equilibrium with the amount of Stx present in the gut, and it is also related to renal and neurologic symptoms. The TLR4-mediated interaction of LPS with innate immune cells is hampered by the well-known antibiotic polymyxin B. In this study, we show that the same antibiotic impairs the binding of Stx to neutrophils, also blocking their functional effects (release of CXCL8, formation of neutrophil/platelet aggregates) involved in HUS pathogenesis. Controls for contaminating LPS in Stx-induced neutrophil responses inhibited by polymyxin B were performed. Stx interact with human neutrophils through their A chain, since these leukocytes do not express globotriaosylceramide, the specific receptor for Stx B chains. Consistently, polymyxin B blocked the enzymatic activity of Stx1, Stx2, Stx1 A chain, and the analogous plant protein gelonin, whereas the antibiotic did not show any protective effect on Stx-induced cytotoxicity in globotriaosylceramide-expressing Raji cells. Antibiotic administration is not recommended in human STEC infections during the prodromal intestinal phase, and the toxicity of polymyxin B could further discourage its therapeutic use. However, nontoxic, nonbactericidal polymyxin derivatives have been developed and might be used in animal models of STEC infection to study their efficacy in preventing the onset of HUS during the systemic blood phase of Stx.