Two SNPs (rs3664408 and rs13476889) of 129S6/Sv background could be discriminated in the MMP-9−/− mice at chromosome 2, related to the region of genetic modification for Mmp9. Over a period of 15 years, no differences in infections or seroconversion against a number of classically tested animal pathogens were observed between sentinel WT and MMP-9−/− mice from the same unique breeding insulator. Here, MMP9 is linked to infection.