An antibody targeting type III secretion system induces broad protection against Salmonella and Shigella infections

Abstract

Salmonella and Shigella bacteria are food- and waterborne pathogens that are responsible for enteric infections in humans and are still the major cause of morbidity and mortality in the emerging countries. The existence of multiple Salmonella and Shigella serotypes as well as the emergence of strains resistant to antibiotics requires the development of broadly protective therapies. Recently, the needle tip proteins of the type III secretion system of these bacteria were successfully utilized (SipD for Salmonella and IpaD for Shigella) as vaccine immunogens to provide good prophylactic cross-protection in murine models of infections. From these experiments, we have isolated a cross-protective monoclonal antibody directed against a conserved region of both proteins. Its conformational epitope determined by Deep Mutational Scanning is conserved among needle tip proteins of all pathogenic Shigella species and Salmonella serovars, and are well recognized by this antibody. Our study provides the first in vivo experimental evidence of the importance of this common region in the mechanism of virulence of Salmonella and Shigella and opens the way to the development of cross-protective therapeutic agents.

Deciphering cross-species reactivity of LAMP-1 antibodies using deep mutational epitope mapping and AlphaFold

“…Had the study been performed with antibodies targeting the same luminal domain, it is possible that mutations affecting the hydrophobic core would have influenced the binding of both molecules, as reported in other studies. 16 …”

“… 12 More specifically, several studies have allowed the identification of the epitope of monoclonal antibodies (mAbs) against prion protein, 13 S. aureus alpha toxin, 14 nerve growth factor 15 and Salmonella antigens. 16 DMS identifies the functional epitope as the key interacting amino acids that cannot be replaced without causing a major loss in binding activity. By extension, DMS has recently proved useful in predicting antigen mutations that allow escape from the action of therapeutic mAbs.…”

Functional assays to evaluate antibody-mediated responses against Shigella: a review

“…Animal anti-sera and monoclonal antibodies against IpaD ( Sierocki et al., 2021 ), IpaB ( Mills et al., 1988 ; Shen et al., 2010 ; Li et al., 2022 ) and IpaC ( Mills et al., 1988 ) were demonstrated to reduce the ability of virulent bacteria to infect in in vitro cell models. These works are in line with studies in animal models in which mice immunized with IpaB and IpaD developed a protective immune response (both IgG and IgA) upon challenge ( Martinez-Becerra et al., 2012 ), therefore demonstrating in vivo the relevance of anti-Ipa antibodies.…”

“…To this date, only Sieroki et al. used contact haemolysis as a functional assay to demonstrate the ability of cross-reactive anti-IpaD ( Shigella ) -SipD ( Salmonella ) monoclonal antibodies to inhibit membrane lysis ( Sierocki et al., 2021 ). Interestingly, the tested antibody (mAb IpaD-318) was found to enhance the haemolysis of erythrocytes, but not HeLa cell invasion.…”

“…Interestingly, the tested antibody (mAb IpaD-318) was found to enhance the haemolysis of erythrocytes, but not HeLa cell invasion. The authors hypothesized that mAb IpaD-318 stabilized polymerized IpaD in an intermediate conformation that lost the capacity to control correct IpaB and IpaC translocation ( Sierocki et al., 2021 ). Antibody fragments against IpaD were also reported to significantly reduce erythrocytes haemolysis by wild-type S. flexneri ( Barta et al., 2017 ).…”