TolC facilitates the intracellular survival and immunomodulation of <i>Salmonella</i> Typhi in human host cells

<i>Salmonella enterica</i> serovar Typhi (<i>S</i>. Typhi) causes typhoid fever, a systemic infection that affects millions of people worldwide. <i>S</i>. Typhi can invade and survive within host cells, such as intestinal epithelial cells and macrophages, by modulating their immune responses. However, the immunomodulatory capability of <i>S</i>. Typhi in relation to TolC-facilitated efflux pump function remains unclear. The role of TolC, an outer membrane protein that facilitates efflux pump function, in the invasion and immunomodulation of <i>S</i>. Typhi, was studied in human intestinal epithelial cells and macrophages. The <i>tolC</i> deletion mutant of <i>S</i>. Typhi was compared with the wild-type and its complemented strain in terms of their ability to invade epithelial cells, survive and induce cytotoxicity in macrophages, and elicit proinflammatory cytokine production in macrophages. The <i>tolC</i> mutant, which has a defective outer membrane, was impaired in invading epithelial cells compared to the wild-type strain, but the intracellular presence of the <i>tolC</i> mutant exhibited greater cytotoxicity and induced higher levels of proinflammatory cytokines (<i>IL-1β</i> and <i>IL-8</i>) in macrophages compared to the wild-type strain. These effects were reversed by complementing the <i>tolC</i> mutant with a functional <i>tolC</i> gene. Our results suggest that TolC plays a role in <i>S</i>. Typhi to efficiently invade epithelial cells and suppress host immune responses during infection. TolC may be a potential target for the development of novel therapeutics against typhoid fever.