54 One of the key findings of Peniche et al. was the importance of IL-22 in the aged mice CDI outcome, demonstrating a lower production of IL-22 in aged mice, and protection of the aged mice when given recombinant IL-22 during infection.19 Since in Peniche et al., recombinant IL-22 was given on day 1 of infection, suggesting a host response-mediated effect on outcome rather than a microbiome-mediated effect. Here, IL22 is linked to clostridium difficile infection.