HTRA1 and infection: Using the IL-10−/− knockout mouse infection model system, the results presented in this study demonstrate for the first time that the C. jejuni HtrA serine protease is a novel virulence factor which aggravates enterocolitis in situ by causing a substantial amount of cell damage, aggravation of intestinal apoptosis and inflammation upon C. jejuni infection in vivo accompanied by significant systemic pro-inflammatory immune responses.