Shigella sonneiinfection of zebrafish reveals that O-antigen mediates neutrophil tolerance and dysentery incidence

Abstract

AbstractShigella flexneriis historically regarded as the primary agent of bacillary dysentery, yet the closely-relatedShigella sonneiis replacingS. flexneri, especially in developing countries. The underlying reasons for this dramatic shift are mostly unknown. Using a zebrafish (Danio rerio) model ofShigellainfection, we discover thatS. sonneiis more virulent thanS. flexneri in vivo. Whole animal dual-RNAseq and testing of bacterial mutants suggest thatS. sonneivirulence depends on its O-antigen oligosaccharide (which is unique amongShigellaspecies). We showin vivousing zebrafish andex vivousing human neutrophils thatS. sonneiO-antigen can mediate neutrophil tolerance. Consistent with this, we demonstrate that O-antigen enablesS. sonneito resist phagolysosome acidification and promotes neutrophil cell death. Chemical inhibition or promotion of phagolysosome maturation respectively decreases and increases neutrophil control ofS. sonneiand zebrafish survival. Strikingly, larvae primed with a sublethal dose ofS. sonneiare protected against a secondary lethal dose ofS. sonneiin an O-antigen-dependent manner, indicating that exposure to O-antigen can train the innate immune system againstS. sonnei. Collectively, these findings reveal O-antigen as an important therapeutic target against bacillary dysentery, and may explain the rapidly increasingS. sonneiburden in developing countries.Author SummaryShigella sonneiis predominantly responsible for dysentery in developed countries, and is replacingShigella flexneriin areas undergoing economic development and improvements in water quality. UsingShigellainfection of zebrafish (in vivo) and human neutrophils (in vitro), we discover thatS. sonneiis more virulent thanS. flexneribecause of neutrophil tolerance mediated by its O-antigen oligosaccharide acquired from the environmental bacteriaPlesiomonas shigelloides. To inspire new approaches forS. sonneicontrol, we show that increased phagolysosomal acidification or innate immune training can promoteS. sonneiclearance by neutrophilsin vivo. These findings have major implications for our evolutionary understanding ofShigella, and may explain why exposure toP. shigelloidesin low and middle-income countries (LMICs) can protect against dysentery incidence.