Intestinal macromolecular transport supporting adaptive immunity

The gastrointestinal tract performs opposing functions of nutrient absorption, barrier maintenance, and the delivery of luminal substances for the appropriate induction of tolerogenic or protective adaptive immunity. The single-layer epithelium lining the gastrointestinal tract is central to each of these functions by facilitating the uptake and processing of nutrients, providing a physical and chemical barrier to potential pathogens, and delivering macromolecular substances to the immune system to initiate adaptive immune responses. Specific transport mechanisms allow nutrient uptake and the delivery of macromolecules to the immune system while maintaining the epithelial barrier. This review examines historical observations supporting macromolecular transport by the intestinal epithelium, recent insights into the transport of luminal macromolecules to promote adaptive immunity, and how this process is regulated to promote appropriate immune responses. Understanding how luminal macromolecules are delivered to the immune system and how this is regulated may provide insight into the pathophysiology of inflammatory diseases of the gastrointestinal tract and potential preventative or therapeutic strategies. Keywords: Antigen Transport, Mucosal Tolerance, Goblet Cell

Isolated lymphoid follicles are dynamic reservoirs for the induction of intestinal IgA

IgA is one of the most important molecules in the regulation of intestinal homeostasis. Peyer’s patches have been traditionally recognized as sites for the induction of intestinal IgA responses, however more recent studies demonstrate that isolated lymphoid follicles (ILFs) can perform this function as well. ILF development is dynamic, changing in response to the luminal microbial burden, suggesting that ILFs play an important role providing an expandable reservoir of compensatory IgA inductive sites. However, in situations of immune dysfunction, ILFs can over-develop in response to uncontrollable enteric flora, resulting in ILF hyperplasia. The ability of ILFs to expand and respond to help control the enteric flora makes this dynamic reservoir an important arm of IgA inductive sites in intestinal immunity

Whole-genome sequencing of African Americans implicates differential genetic architecture in inflammatory bowel disease

Whether or not populations diverge with respect to the genetic contribution to risk of specific complex diseases is relevant to understanding the evolution of susceptibility and origins of health disparities. Here, we describe a large-scale whole-genome sequencing study of inflammatory bowel disease encompassing 1,774 affected individuals and 1,644 healthy control Americans with African ancestry (African Americans). Although no new loci for inflammatory bowel disease are discovered at genome-wide significance levels, we identify numerous instances of differential effect sizes in combination with divergent allele frequencies. For example, the major effect at PTGER4 fine maps to a single credible interval of 22 SNPs corresponding to one of four independent associations at the locus in European ancestry individuals but with an elevated odds ratio for Crohn disease in African Americans. A rare variant aggregate analysis implicates C

RNF20 and RNF40 regulate vitamin D receptor-dependent signaling in inflammatory bowel disease

Despite the identification of several genetic factors linked to increased susceptibility to inflammatory bowel disease (IBD), underlying molecular mechanisms remain to be elucidated in detail. The ubiquitin ligases RNF20 and RNF40 mediate the monoubiquitination of histone H2B at lysine 120 (H2Bub1) and were shown to play context-dependent roles in the development of inflammation. Here, we aimed to examine the function of the RNF20/RNF40/H2Bub1 axis in intestinal inflammation in IBD patients and mouse models. For this purpose, intestinal sections from IBD patients were immunohistochemically stained for H2Bub1. Rnf20 or Rnf40 were conditionally deleted in the mouse intestine and mice were monitored for inflammation-associated symptoms. Using mRNA-seq and chromatin immunoprecipitation (ChIP)-seq, we analyzed underlying molecular pathways in primary intestinal epithelial cells (IECs) isolated from these animals and confirmed these findings in IBD resection specimens using ChIP-seq.The majority (80%) of IBD patients displayed a loss of H2Bub1 levels in inflamed areas and the intestine-specific deletion of Rnf20 or Rnf40 resulted in spontaneous colorectal inflammation in mice. Consistently, deletion of Rnf20 or Rnf40 promoted IBD-associated gene expression programs, including deregulation of various IBD risk genes in these animals. Further analysis of murine IECs revealed that H3K4me3 occupancy and transcription of the Vitamin D Receptor (Vdr) gene and VDR target genes is RNF20/40-dependent. Finally, these effects were confirmed in a subgroup of Crohn\u27s disease patients which displayed epigenetic and expression changes in RNF20/40-dependent gene signatures. Our findings reveal that loss of H2B monoubiquitination promotes intestinal inflammation via decreased VDR activity thereby identifying RNF20 and RNF40 as critical regulators of IBD

Regulatory T cells developing peri-weaning are continually required to restrain Th2 systemic responses later in life

Atopic disorders including allergic rhinitis, asthma, food allergy, and dermatitis, are increasingly prevalent in Western societies. These disorders are largely characterized by T helper type 2 (Th2) immune responses to environmental triggers, particularly inhaled and dietary allergens. Exposure to such stimuli during early childhood reduces the frequency of allergies in at-risk children. These allergic responses can be restrained by regulatory T cells (Tregs), particularly Tregs arising in the gut. The unique attributes of how early life exposure to diet and microbes shape the intestinal Treg population is a topic of significant interest. While imprinting during early life promotes the development of a balanced immune system and protects against immunopathology, it remains unclear if Tregs that develop in early life continue to restrain systemic inflammatory responses throughout adulthood. Here, an inducible deletion strategy was used to label Tregs at specified time points with a targeted mechanism to be deleted later. Deletion of the Tregs labeled peri-weaning at day of life 24, but not before weaning at day of life 14, resulted in increased circulating IgE and IL-13, and abrogated induction of tolerance towards new antigens. Thus, Tregs developing peri-weaning, but not before day of life 14 are continually required to restrain allergic responses into adulthood

An Ileal Crohn's Disease Gene Signature Based on Whole Human Genome Expression Profiles of Disease Unaffected Ileal Mucosal Biopsies

Previous genome-wide expression studies have highlighted distinct gene expression patterns in inflammatory bowel disease (IBD) compared to control samples, but the interpretation of these studies has been limited by sample heterogeneity with respect to disease phenotype, disease activity, and anatomic sites. To further improve molecular classification of inflammatory bowel disease phenotypes we focused on a single anatomic site, the disease unaffected proximal ileal margin of resected ileum, and three phenotypes that were unlikely to overlap: ileal Crohn's disease (ileal CD), ulcerative colitis (UC), and control patients without IBD. Whole human genome (Agilent) expression profiling was conducted on two independent sets of disease-unaffected ileal samples collected from the proximal margin of resected ileum. Set 1 (47 ileal CD, 27 UC, and 25 Control non-IBD patients) was used as the training set and Set 2 was subsequently collected as an independent test set (10 ileal CD, 10 UC, and 10 control non-IBD patients). We compared the 17 gene signatures selected by four different feature-selection methods to distinguish ileal CD phenotype with non-CD phenotype. The four methods yielded different but overlapping solutions that were highly discriminating. All four of these methods selected FOLH1 as a common feature. This gene is an established biomarker for prostate cancer, but has not previously been associated with Crohn's disease. Immunohistochemical staining confirmed increased expression of FOLH1 in the ileal epithelium. These results provide evidence for convergent molecular abnormalities in the macroscopically disease unaffected proximal margin of resected ileum from ileal CD subjects

Intestinal goblet cells sample and deliver lumenal antigens by regulated endocytic uptake and transcytosis

Intestinal goblet cells maintain the protective epithelial barrier through mucus secretion and yet sample lumenal substances for immune processing through formation of goblet cell associated antigen passages (GAPs). The cellular biology of GAPs and how these divergent processes are balanced and regulated by goblet cells remains unknown. Using high-resolution light and electron microscopy, we found that in mice, GAPs were formed by an acetylcholine (ACh)-dependent endocytic event remarkable for delivery of fluid-phase cargo retrograde into the trans-golgi network and across the cell by transcytosis - in addition to the expected transport of fluid-phase cargo by endosomes to multi-vesicular bodies and lysosomes. While ACh also induced goblet cells to secrete mucins, ACh-induced GAP formation and mucin secretion were functionally independent and mediated by different receptors and signaling pathways, enabling goblet cells to differentially regulate these processes to accommodate the dynamically changing demands of the mucosal environment for barrier maintenance and sampling of lumenal substances

Identification of gut bacteria such as Lactobacillus johnsonii that disseminate to systemic tissues of wild type and MyD88-/- mice

In healthy hosts the gut microbiota is restricted to gut tissues by several barriers some of which require MyD88-dependent innate immune sensor pathways. Nevertheless, some gut taxa have been reported to disseminate to systemic tissues. However, the extent to which this normally occurs during homeostasis in healthy organisms is still unknown. In this study, we recovered viable gut bacteria from systemic tissues of healthy wild type (WT) and MyD8