Abstract
Foodborne salmonellosis is one of the most important bacterial zoonotic diseases worldwide. Salmonella Typhimurium is the serovar most frequently isolated from persistently infected slaughter pigs in Europe. Circumvention of the host’s immune system by Salmonella might contribute to persistent infection of pigs. In the present study, we found that Salmonella Typhimurium strain 112910a specifically downregulated MHC II, but not MHC I, expression on porcine alveolar macrophages in a Salmonella pathogenicity island (SPI)-1 and SPI-2 dependent way. Salmonella induced downregulation of MHC II expression and intracellular proliferation of Salmonella in macrophages were significantly impaired after opsonization with Salmonella specific antibodies prior to inoculation. Furthermore, the capacity to downregulate MHC II expression on macrophages differed significantly among Salmonella strains, independently of strain specific differences in invasion capacity, Salmonella induced cytotoxicity and altered macrophage activation status. The fact that strain specific differences in MHC II downregulation did not correlate with the extent of in vitro SPI-1 or SPI-2 gene expression indicates that other factors are involved in MHC II downregulation as well. Since Salmonella strain dependent interference with the pig’s immune response through downregulation of MHC II expression might indicate that certain Salmonella strains are more likely to escape serological detection, our findings are of major interest for Salmonella monitoring programs primarily based on serology.
Highlights
Nontyphoidal salmonellosis is one of the most important bacterial zoonotic diseases, yearly resulting in an estimated 155 000 deaths worldwide [1]
We examined whether a Salmonella Typhimurium strain, which can persist in pigs, is able to downregulate MHC expression on porcine macrophages in a Salmonella pathogenicity island (SPI)-1 and/or SPI-2 dependent way, as a possible mechanism to circumvent antibody production by the pig’s immune system
We found that Salmonella Typhimurium strain 112910a downregulated MHC II expression on the surface of macrophages and that the MHC I level of macrophages remained unaffected 24 h post inoculation
Summary
Nontyphoidal salmonellosis is one of the most important bacterial zoonotic diseases, yearly resulting in an estimated 155 000 deaths worldwide [1]. After infection by a pathogen, the host’s immune system will respond through an innate and a subsequent adaptive immune response. The success of many persisting pathogens relies on their ability to resist, circumvent or counteract the host’s innate and/or adaptive immune responses. Salmonella exhibits host specific behaviour and no data are available yet on this phenomenon in pigs. It is not known whether different Salmonella strains might be able to interfere differentially with the MHC II expression pathway in porcine cells. By manipulating the porcine humoral immune response, certain Salmonella strains might be able to persist better than strains that do not interfere with the immune response in pigs
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