As described earlier, we did not observe any differences in infections or seroconversion against a number of classically tested animal pathogens between sentinel WT and MMP-9-/- mice from the same unique breeding insulator over a period of 15 years.9 During our colitis experiments, WT and MMP-9-/- mice were co-housed according to phenotype. The gene discussed is MMP9; the disease is colitis.