Understanding human Crohns disease: T cell immunoprofiling and in vitro primary intestinal epithelial monolayer models

Abstract Crohn’s disease (CD) is a type of inflammatory bowel disease caused by uncontrolled inflammation and is associated with loss of tolerance to commensal bacteria. There is no current consensus on how CD forms; however, four susceptibility criteria are required for disease: a microbial presence, an immune response, an environmental trigger, and genetic susceptibility. We investigated the peripheral and intestinal immune response of people with CD compared to healthy people. CD peripheral blood (PBMC) contained higher baseline frequencies of pro-inflammatory Th17 cells compared to those from healthy controls, and regulatory T cells from CD patients increased in frequency in response to the commensal Faecalibacterium prausnitzii, whereas those from healthy controls did not. CD patient PBMCs secreted higher concentrations of the pro-inflammatory cytokines: IL-6, TNF, and IL-17A, compared to healthy controls. We developed a human 2-dimensional large intestine organoid monolayer transwell model that replicates the in vivo intestinal epithelial barrier as the cells of the epithelial monolayer are arranged into a selectively semi-permeable polarised membrane, separating the apical and basal regions of the system, emulating the luminal and lamina propria intestinal regions. Co-culture of CD patient-derived monolayers with patient PBMCs and heat-killed F. prausnitzii caused disruption of monolayer integrity, whereas control patient monolayers were unaffected. IL-6 was present in control monolayer supernatants but not those from CD patients. We hypothesise that CD patient PBMCs have inherent abnormal responses to commensal bacteria, and in the context of this model, IL-6 may be required for maintenance of monolayer integrity.