CELLULAR AND MOLECULAR INTERACTION OF MAIT CELLS IN MUCOSAL TISSUE AND THEIR ROLE IN IBD

Introduction Inflammatory bowel disease (IBD) manifests as chronic inflammation of the gastrointestinal tract and is characterized by a deregulated immune response targeting the gut microflora. The identification of the immune cells involved in this pathology represents a major objective to unravel the underlying pathophysiological mechanisms and may suggest new therapeutic strategies. Recently, MAIT cells, a relatively abundant T cell subset, has been identified as a possible key player in IBD. Upon activation, they produce cytokines including IL-26, a newly discovered cytokine involved in the pathology of IBD. Interestingly, its role in the course of inflammation has not been fully investigated. Studies employing human cell cultures provide limited results as they cannot fully mimic the complex 3D structure of the intestinal tissue. Great hope is placed in the development of models of human diseases using intestinal organoids (IOs) - 3D structures that recapitulate the architecture and functionality of tissue. Methods We are using IOs derived from iPSC as in vitro model of intestinal tissue. We describe them using various methods such as immunofluorescent labelling, flow cytometry, RNAseq, qPCR and WB. We sort the MAIT cells using FACS sorting and stimulate them in vitro. We study their response using qPCR, intracellular staining and subsequent flow cytometry. Results IOs respond to stimulation with various stimuli by producing pro-inflammatory cytokines including those activating MAIT cells. Moreover, IOs express MR1 which is recognised by the invariant TCR receptor of the MAIT cells. IOs express the IL-26 receptor and respond to this cytokine by increased phosphorylation of STAT3. We show that MAIT cells can be isolated from human blood. Upon in vitro activation, they produce cytokines and effector molecules including IL-26 and their response differs depending on the origin of the stimuli. Conclusions IOs form complex structures and immunocompetent environment allowing to study of intestinal inflammation. IOs consist of various cell types, but not immune cells. Taken together with MR1 and cytokines expression we show that IOs can activate MAIT cells, and they serve as a relevant model for in vitro study of MAIT cells. Moreover, organoids respond to IL-26, so they also provide a relevant model to elucidate the role of this cytokine. We expect that this study will contribute to our understanding of the processes underlying the onset and progression of IBD and the role of MAIT cells in the course of inflammation, and lead to the design of new therapeutic targets.