T-Cell Cytokine Response in Salmonella Typhimurium-Vaccinated versus Infected Pigs

Development of Live Attenuated Salmonella Typhimurium Vaccine Strain Using Radiation Mutation Enhancement Technology (R-MET)

Salmonella enterica is a leading cause of food-borne diseases in humans worldwide, resulting in severe morbidity and mortality. They are carried asymptomatically in the intestine or gallbladder of livestock, and are transmitted predominantly from animals to humans via the fecal-oral route. Thus, the best preventive strategy is to preemptively prevent transmission to humans by vaccinating livestock. Live attenuated vaccines have been mostly favored because they elicit both cellular and humoral immunity and provide long-term protective immunity. However, developing these vaccines is a laborious and time-consuming process. Therefore, most live attenuated vaccines have been mainly used for phenotypic screening using the auxotrophic replica plate method, and new types of vaccines have not been sufficiently explored. In this study, we used Radiation-Mutation Enhancement Technology (R-MET) to introduce a wide variety of mutations and attenuate the virulence of Salmonella spp. to develop live vaccine strains. The Salmonella Typhimurium, ST454 strain (ST WT) was irradiated with Cobalt60 gamma-irradiator at 1.5 kGy for 1 h to maximize the mutation rate, and attenuated daughter colonies were screened using in vitro macrophage replication capacity and in vivo mouse infection assays. Among 30 candidates, ATOMSal-L6, with 9,961-fold lower virulence than the parent strain (ST454) in the mouse LD50 model, was chosen. This vaccine candidate was mutated at 71 sites, and in particular, lost one bacteriophage. As a vaccine, ATOMSal-L6 induced a Salmonella-specific IgG response to provide effective protective immunity upon intramuscular vaccination of mice. Furthermore, when mice and sows were orally immunized with ATOMSal-L6, we found a strong protective immune response, including multifunctional cellular immunity. These results indicate that ATOMSal-L6 is the first live vaccine candidate to be developed using R-MET, to the best of our knowledge. R-MET can be used as a fast and effective live vaccine development technology that can be used to develop vaccine strains against emerging or serotype-shifting pathogens.

Local and Systemic T Cell Immunity in Fighting Pig Viral and Bacterial Infections

T cells are an essential component of the adaptive immune system. Over the last 15 years, a constantly growing toolbox with which to study T cell biology in pigs has allowed detailed investigations on these cells in various viral and bacterial infections. This review provides an overview on porcine CD4, CD8, and γδ T cells and the current knowledge on the differentiation of these cells following antigen encounter. Where available, the responses of these cells to viral infections like porcine reproductive and respiratory syndrome virus, classical swine fever virus, swine influenza A virus, and African swine fever virus are outlined. In addition, knowledge on the porcine T cell response to bacterial infections like Actinobacillus pleuropneumoniae and Salmonella Typhimurium is reviewed. For CD4 T cells, the response to the outlined infections is reflected toward the Th1/Th2/Th17/Tfh/Treg paradigm for functional differentiation. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.