Cytokine response of porcine cell lines to Salmonella enterica serovar typhimurium and its hilA and ssrA mutants

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative intracellular bacterium which can infect and colonize pigs. After contact with enterocytes and macrophages, S. Typhimurium induces production of cytokines thus triggering the innate immune response. In this study we evaluated the cytokine response of two porcine cell lines, IPI-2I and 3D4/31, of epithelial or macrophage origins, respectively, to the wild-type S. Typhimurium and its hilA and ssrA mutants. We observed that the 3D4/31 cell line essentially did not respond to S. Typhimurium infection when a medium with foetal calf serum was used. However when the 3D4 cell line was incubated overnight in the presence of porcine serum, it efficiently responded to the wild-type strain and the ssrA mutant but not to the noninvasive hilA mutant as measured by mRNA quantification of TNF-alpha, IL-8 and GM-CSF by the real-time RT-PCR. In IPI-2I, all the cytokines were also induced by the wild-type S. Typhimurium and the ssrA mutant although the induction of TNF-alpha was lower than that induced by the wild-type strain. The hilA mutant was unable to induce any of the cytokines tested. The ssrA mutant can therefore be considered as more suitable for further vaccine development as the stimulation of innate immune response is important for animal protection against a challenge with virulent strains.