ISG15 and infection: Eighteen of the up-regulated genes were categorized to the same processes found to be modulated by Salmonella in the colonic mucosa in the time course infection study, i.e. the transporter Clca6, the oxidative stress genes Gpx2 and Duox2, the immune response genes Il1b and T2bp, the antimicrobial defense gene Pla2g2a the inflammatory response genes Pap, Tgm2 and Reg3g, the interferon related genes Ifi47, Gbp2, Iigp2, P47Iigp, Stat1, G1p2 and the proteasome related genes Psmb9, Prss22, Psmb10, Ubd (Table 2).