Although irg1l is also up-regulated during systemic infection, its expression kinetics in embryos immersed in E. tarda is very different from that of well-known inflammation genes such as il1b and mmp9. Considering the important function of epithelial cells in cross talk with cells of the innate immune system, as recently underscored by studies in zebrafish [31], further analysis of infection modes using the identified marker genes will help to better understand the systemic response of tissues toward an infection in a whole organism context. Here, MMP9 is linked to infection.