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There are many different animal models available for studying the pathogenesis of human inflammatory bowel diseases (IBD), each with its own advantages and disadvantages. We describe here an experimental colitis model that is initiated by adoptive transfer of syngeneic splenic CD4(+)CD45RB(high) T cells into T and B cell deficient recipient mice. The CD4(+)CD45RB(high) T cell population that largely consists of naïve effector cells is capable of inducing chronic intestinal inflammation, closely resembling key aspects of human IBD. This method can be manipulated to study aspects of disease onset and progression. Additionally it can be used to study the function of innate, adaptive, and regulatory immune cell populations, and the role of environmental exposures, i.e., the microbiota, in intestinal inflammation. In this article we illustrate the methodology for inducing colitis with a step-by-step protocol. This includes a video demonstration of key technical aspects required to successfully develop this murine model of experimental colitis for research purposes.

There are many different animal models available for studying the pathogenesis of human inflammatory bowel diseases (IBD), each with its own advantages and disadvantages. We describe here an experimental colitis model that is initiated by adoptive transfer of syngeneic splenic CD4+CD45RBhigh T cells into T and B cell deficient recipient mice. The CD4+CD45RBhigh T cell population that largely consists of naïve effector cells is capable of inducing chronic intestinal inflammation, closely resembling key aspects of human IBD. This method can be manipulated to study aspects of disease onset and progression. Additionally it can be used to study the function of innate, adaptive, and regulatory immune cell populations, and the role of environmental exposures, i.e., the microbiota, in intestinal inflammation. In this article we illustrate the methodology for inducing colitis with a step-by-step protocol. This includes a video demonstration of key technical aspects required to successfully develop this murine model of experimental colitis for research purposes.

The p110δ subunit of class IA PI3K modulates signaling in innate immune cells. We previously demonstrated that mice harboring a kinase-dead p110δ subunit (p110δ(KD)) develop spontaneous colitis. Macrophages contributed to the Th1/Th17 cytokine bias in p110δ(KD) mice through increased IL-12 and IL-23 expression. In this study, we show that the enteric microbiota is required for colitis development in germfree p110δ(KD) mice. Colonic tissue and macrophages from p110δ(KD) mice produce significantly less IL-10 compared with wild-type mice. p110δ(KD) APCs cocultured with naive CD4+ Ag-specific T cells also produce significantly less IL-10 and induce more IFN-γ- and IL-17A-producing CD4+ T cells compared with wild-type APCs. Illustrating the importance of APC-T cell interactions in colitis pathogenesis in vivo, Rag1(-/-)/p110δ(KD) mice develop mild colonic inflammation and produced more colonic IL-12p40 compared with Rag1(-/-) mice. However, CD4+ CD45RB(high/low) T cell Rag1(-/-)/p110δ(KD) recipient mice develop severe colitis with increased percentages of IFN-γ- and IL-17A-producing lamina propria CD3+D4+ T cells compared with Rag1(-/-) recipient mice. Intestinal tissue samples from patients with Crohn's disease reveal significantly lower expression of PIK3CD compared with intestinal samples from non-inflammatory bowel disease control subjects (p < 0.05). PIK3CD expression inversely correlates with the ratio of IL12B:IL10 expression. In conclusion, the PI3K subunit p110δ controls homeostatic APC-T cell interactions by altering the balance between IL-10 and IL-12/23. Defects in p110δ expression and/or function may underlie the pathogenesis of human inflammatory bowel disease and lead to new therapeutic strategies.

NFIL3 (nuclear factor, IL-3 regulated) is a transcription factor that regulates multiple immunologic functions. In myeloid cells, NFIL3 is IL-10 inducible, and has a key role as a repressor of IL-12p40 transcription. NFIL3 is a susceptibility gene for the human inflammatory bowel diseases. Here we describe spontaneous colitis in Nfil3−/− mice. Mice lacking both Nfil3 and Il10 (NIDKO) had severe early-onset colitis, suggesting NFIL3 and IL-10 independently regulate mucosal homeostasis. Lymphocytes were necessary for colitis, as Nfil3/Rag1 double knockout (NRDKO) mice were protected from disease. However, NRDKO mice adoptively transferred with wild type CD4+ T cells developed severe colitis compared to Rag1−/− recipients, suggesting that colitis was linked to defects in innate immune cells. Colitis was abrogated in Nfil3/Il12b double-deficient mice, identifying Il12b dysregulation as a central pathogenic event. Finally, germ-free Nfil3−/− mice do not have colonic inflammation. Thus, NFIL3 is a microbiota-dependent, IL-10-independent regulator of mucosal homeostasis via IL-12p40.

The human inflammatory bowel diseases (IBDs), Crohn’s disease (CD) and ulcerative colitis, result from an inappropriately directed immune response to enteric microbiota in a genetically susceptible host. IBDs represent an increasing burden on the global health care system, as incidence is increasing and effective therapies remain elusive. Genome-wide association studies highlight the importance of host innate immune cell-microbial interactions in the pathogenesis of IBDs. PI3K signaling regulates diverse functions, including cell growth, differentiation, proliferation and survival. The Class IA PI3K catalytic subunit p110δ negatively regulates toll-like receptor signaling in innate immune cells. The importance of p110δ in intestinal homeostasis is shown in a mouse harboring a kinase-dead p110δ (p110δKD) that develops spontaneous Th1/Th17-skewed colitis. We describe a requirement for the enteric microbiota to drive intestinal inflammation in p110δKD mice. Microbial-innate immune interactions maintain homeostasis through regulation of both protective (IL-10) and inflammatory (IL-12p40) cytokines, and p110δ is a central regulator of this balance. Additionally, p110δ positively regulates eradication of intracellular bacteria in macrophages. Persistence of intracellular bacteria and chronic stimulation in intestinal p110δKD macrophages propagates the cytokine imbalance. Furthermore, p110δ orchestrates innate immune cell regulation of pathogenic adaptive immune responses. Importantly, in human CD, decreased intestinal PIK3CD gene expression and an inverse correlation with intestinal IL12B:IL10 ratios are demonstrated. Thus, p110δ appears to be a central homeostatic switch in the intestine, governing the critical balance between IL- 12/23 and IL-10 induced by the microbiota that determines the subsequent T cell response. Counter to prevailing paradigms where p110δ inhibition is a strategic approach in inflammatory diseases, strategies to induce p110δ gene expression could be a potential therapeutic approach in human IBDs.

Background and Aims: The host receptor for SARS-CoV-2, angiotensin-converting enzyme 2 (ACE2), is highly expressed in small intestine. Our aim was to study colonic ACE2 expression in Crohn's disease (CD) and non-inflammatory bowel disease (non-IBD) controls. We hypothesized that the colonic expression levels of ACE2 impacts CD course., Methods: We examined the expression of colon ACE2 using RNA-seq and quantitative (q) RT-PCR from 69 adult CD and 14 NIBD control patients. In a subset of this cohort we validated ACE2 protein expression and localization in formalin-fixed, paraffin-embedded matched colon and ileal tissues using immunohistochemistry. The impact of increased ACE2 expression in CD for the risk of surgery was evaluated by a multivariate regression analysis and a Kaplan-Meier estimator. To provide critical support for the generality of our findings, we analyzed previously published RNA-seq data from two large independent cohorts of CD patients., Results: Colonic ACE2 expression was significantly higher in a subset of adult CD patients (ACE2-high CD). IHC in a sampling of ACE2-high CD patients confirmed high ACE2 protein expression in the colon and ileum compared to ACE2-low CD and NIBD patients. Notably, we found that ACE2-high CD patients are significantly more likely to undergo surgery within 5 years of diagnosis, with a Cox regression analysis finding that high ACE2 levels is an independent risk factor (OR 2.18; 95%CI, 1.05-4.55; p=0.037)., Conclusion: Increased intestinal expression of ACE2 is associated with deteriorated clinical outcomes in CD patients. These data point to the need for molecular stratification that may impact CD disease-related outcomes.