Investigating the Role of HOIL1 in Controlling Citrobacter rodentium Pathogenesis

HOIL1-deficient patients experience chronic intestinal inflammation and diarrhea as well as increased susceptibility to certain bacterial infections. HOIL1 is a component of the linear ubiquitin chain assembly complex (LUBAC) that regulates immune signaling pathways including NFκB-activating pathways. We have shown previously that HOIL1 is essential for survival following Citrobacter rodentium gastrointestinal infection of mice, but the mechanism of protection by HOIL1 was not examined. C. rodentium is a murine model for human attaching and effacing (A/E) pathogens, enteropathogenic and enterohemorrhagic Escherichia coli, that cause diarrhea and food-borne illnesses, and lead to severe disease in children and immunocompromised individuals. Here, we found that C. rodentium infection caused severe colitis and dissemination of C. rodentium to systemic organs in Hoil1-/- mice. HOIL1 was important in the innate immune response to limit C. rodentium replication in the intestine, and to modulate induction of inflammatory cytokines. Using cell type-specific knock-out mice, we found that HOIL1 was dispensable in intestinal epithelial cells (IEC), but was required in CD11c- and lysozyme 2-expressing myeloid cells to prevent weight loss and systemic dissemination of C. rodentium. While HOIL1-deficiency did not affect populations of neutrophils or macrophages, dendritic cells and group 3 innate lymphoid cell (ILC3) numbers were reduced, resulting in a defect in IL-22 induction during C. rodentium infection. Understanding the role HOIL1 plays in limiting the pathogenesis of A/E lesion-forming bacteria will provide further insights into the innate immune response to gastrointestinal pathogens and inflammatory disorders.