The gastrointestinal (GI) tract is a crucial interface for the host, food derived antigens, the commensal microbiota and invasive pathogens. Here, the immune system must simultaneously protect against harmful pathogens and remain tolerogenic to commensal bacteria and nutrients. The intestinal mucosa of adult humans and mice is enriched for innate lymphoid cells (ILCs) that express the transcription factor RORγt (ILC3s). These cells are crucial for maintaining the delicate balance of tolerance and immunity in the GI tract. They serve protective roles in immune responses to infectious organisms, are essential for the formation of lymphoid tissues, and help maintain gut homeostasis via signaling to epithelial cells through interleukin 22 (IL-22).
ILC3s in the GI tract can be further categorized into three main subsets with distinct and overlapping functional roles. These subsets can be identified by either the expression of CCR6, Nkp46, or by lacking both markers- double negative (DN), some of which also make IL-17A. Signals that mediate the development and function of the various ILC3 subsets are still an area of active investigation. Notch signaling is a highly conserved pathway that contributes to the development and function of many types of immune cells. There has been some investigation into the role Notch signaling plays in the development of ILC3, particularly in the transition from DN to Nkp46 ILC3.
However, all three subsets of ILC3s express two Notch receptor isoforms (Notch1 and Notch2) the individual roles of these two receptors have not been dissected. We show signaling through Notch1 and Notch2 individually contribute to Nkp46 ILC3 development in a cell intrinsic manner. We also show Notch signaling, primarily through Notch2, reinforces the ILC3 program and suppresses the ILC1-like program in Nkp46 ILC3 by promoting the expression of RORγt, c-Maf, and IL-22, and suppressing the expression of T-bet and IFNγ. Notch signaling also supports ILC3-identity genes in CCR6 ILC3, promoting RORγt, IL-17A, and IL-22. We, therefore, identify a novel role for Notch signaling in ILC3 function. As such, Notch-deficient ILC3 fail to initiate proper immune response to enteric pathogen Citrobacter rodentium, leading to more severe infection. Our results show how a highly conserved signaling pathway contributes to ILC3 development, identity, and function.
The GI tract is also enriched with helper CD4 T cells that express RORγt, IL-17A, and IL-22 (Th17), which share many phenotypic and functional features with ILC3. The relative contribution of ILC3 and Th17 cells to immune phenotypes remains poorly understood. Moreover, due to the lack of ILC3-specific depletion models, how ILC3 regulate mucosal protection in the presence of Th17 cells is not clear. Here, we examined non-redundant functions of ILC3 in intestinal immunity using novel ILC3-deficient mice that maintain endogenous T cells, Th17 cells, and secondary lymphoid organs. ILC3 depletion did not affect IL-22-production by CD4 T cells during homeostasis.
However, despite the presence of IL-22-producing T cells, ILC3 and ILC3- derived IL-22 were required for maintaining homeostatic functions of the intestinal epithelium. ILC3 were dispensable for generation of Th17 and Th22 cell responses to pathogenic bacteria, though Th17 and Th22 responses were delayed in the absence of ILC3. ILC3- deficient mice were capable of pathogen clearance and survived infection with low dose Citrobacter rodentium in the presence of antigen-specific Th17 cells. However, ILC3 increased pathogen tolerance at early timepoints of infection by activating tissue-protective immune pathways. Consequently, ILC3 were indispensable for survival of high dose infection.
We also assess the role of ILC3 and Th17 cell in metabolic syndrome, using our novel model. Our lab demonstrated commensal-specific Th17 cells are protective against metabolic syndrome and lost under high-fat, high-sugar diet. ILC3s drive the expansion of a commensal member, Faecalibaculum rodentium (F. rod), which displaces the Th17 cell-inducing commensal, segemented filamentous bacteria (SFB). Without ILC3s, SFB is not lost from the microbiota, commensal- specific Th17 cells are maintained and there is, therefore, no development of metabolic syndrome. Our results demonstrate crucial context- dependent roles for ILC3 in immune-sufficient animals during homeostasis, infection, and metabolic disease.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/3a97-px96 |
| Date | January 2024 |
| Creators | Edwards, Madeline Elizabeth |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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