HTRA1 and infection: The idea that the protease activity of HtrA triggers inflammatory processes in host cells is further underlined by lower numbers of immune cells at the site of infection and less secretion of pro-inflammatory cytokines in intestinal, but also extra-intestinal and, remarkably, even systemic compartments following C. jejuni 11168HtrA−S197A as compared to 11168WT strain infection as shown here and in our previous studies with the C. jejuni ΔhtrA mutant vs. parental strain (Heimesaat et al., 2014a,b).