Enrichment of IL-17A+ IFN-γ+ and IL-22+ IFN-γ+ T cell subsets is associated with reduction of NKp44+ ILC3s in the terminal ileum of Crohn's disease patients

Abstract

Crohn's disease (CD) is a chronic inflammatory condition of the human gastrointestinal tract whose aetiology remains largely unknown. Dysregulated adaptive immune responses and defective innate immunity both contribute to this process. In this study, we demonstrated that the interleukin (IL)-17A⁺ interferon (IFN)-γ⁺ and IL-22⁺ IFN-γ⁺ T cell subsets accumulated specifically in the inflamed terminal ileum of CD patients. These cells had higher expression of Ki-67 and were active cytokine producers. In addition, their proportions within both the IL-17A-producer and IL-22-producer populations were increased significantly. These data suggest that IL-17A⁺ IFN-γ⁺ and IL-22⁺ IFN-γ⁺ T cell subsets might represent the pathogenic T helper type 17 (Th17) population in the context of intestinal inflammation for CD patients. In the innate immunity compartment we detected a dramatic alteration of both phenotype and function of the intestinal innate lymphoid cells (ILCs), that play an important role in the maintenance of mucosal homeostasis. In the inflamed gut the frequency of the NKp44^- CD117^- ILC1s subset was increased significantly, while the frequency of NKp44⁺ ILC3s was reduced. Furthermore, the frequency of human leucocyte antigen D-related (HLA-DR)-expressing-NKp44⁺ ILC3s was also reduced significantly. Interestingly, the decrease in the NKp44⁺ ILC3s population was associated with an increase of pathogenic IL-17A⁺ IFN-γ⁺ and IL-22⁺ IFN-γ⁺ T cell subsets in the adaptive compartment. This might suggest a potential link between NKp44⁺ ILC3s and the IL-17A⁺ IFN-γ⁺ and IL-22⁺ IFN-γ⁺ T cell subsets in the terminal ileum of CD patients.

Keywords: Crohn's disease; T cells; innate lymphoid cells.