Intestinal intraepithelial lymphocyte activation promotes innate antiviral resistance

γδ T cells in homeostasis and host defence of epithelial barrier tissues

Epithelial surfaces line the body and provide a crucial interface between the body and the external environment. Tissue-resident epithelial γδ T cells represent a major T cell population in the epithelial tissues and are ideally positioned to carry out barrier surveillance and aid in tissue homeostasis and repair. In this Review, we focus on the intraepithelial γδ T cell compartment of the two largest epithelial tissues in the body - namely, the epidermis and the intestine - and provide a comprehensive overview of the crucial contributions of intraepithelial γδ T cells to tissue integrity and repair, host homeostasis and protection in the context of the symbiotic relationship with the microbiome and during pathogen clearance. Finally, we describe epithelium-specific butyrophilin-like molecules and briefly review their emerging role in selectively shaping and regulating epidermal and intestinal γδ T cell repertoires.

Interferon-Lambda: A Potent Regulator of Intestinal Viral Infections

Interferon-lambda (IFN-λ) is a recently described cytokine found to be of critical importance in innate immune regulation of intestinal viruses. Endogenous IFN-λ has potent antiviral effects and has been shown to control multiple intestinal viruses and may represent a factor that contributes to human variability in response to infection. Importantly, recombinant IFN-λ has therapeutic potential against enteric viral infections, many of which lack other effective treatments. In this mini-review, we describe recent advances regarding IFN-λ-mediated regulation of enteric viruses with important clinical relevance including rotavirus, reovirus, and norovirus. We also briefly discuss IFN-λ interactions with other cytokines important in the intestine, and how IFN-λ may play a role in regulation of intestinal viruses by the commensal microbiome. Finally, we indicate currently outstanding questions regarding IFN-λ control of enteric infections that remain to be explored to enhance our understanding of this important immune molecule.

Contribution of type III interferons to antiviral immunity: location, location, location

Type I interferons (IFN-α/β) and the more recently identified type III IFNs (IFN-λ) function as the first line of defense against virus infection and regulate the development of both innate and adaptive immune responses. Type III IFNs were originally identified as a novel ligand-receptor system acting in parallel with type I IFNs, but subsequent studies have provided increasing evidence for distinct roles for each IFN family. In addition to their compartmentalized antiviral actions, these two systems appear to have multiple levels of cross-regulation and act coordinately to achieve effective antimicrobial protection with minimal collateral damage to the host.

Type 1 Interferon in the Human Intestine-A Co-ordinator of the Immune Response to the Microbiota

The human gut is in constant complex interaction with the external environment. Although much is understood about the composition and function of the microbiota, much remains to be learnt about the mechanisms by which these organisms interact with the immune system in health and disease. Type 1 interferon (T1IFN), a ubiquitous and pleiotropic family of cytokines, is a critical mediator of the response to viral, bacterial, and other antigens sampled in the intestine. Although inflammation is enhanced in mouse model of colitis when T1IFN signaling is lost, the action of T1IFN is context specific and can be pro- or anti-inflammatory. In humans, T1IFN has been used to treat inflammatory diseases, including multiple sclerosis and inflammatory bowel disease but intestinal inflammation can also develop after the administration of T1IFN. Recent findings indicate that "tonic" or "endogenous" T1IFN, induced by signals from the commensal microbiota, modulates the local signaling environment to prime the intestinal mucosal immune system to determine later responses to pathogens and commensal organisms. This review will summarize the complex immunological effects of T1IFN and recent the role of T1IFN as a mediator between the microbiota and the mucosal immune system, highlighting human data wherever possible. It will discuss what we can learn from clinical experiences with T1IFN and how the T1IFN pathway may be manipulated in the future to maintain mucosal homeostasis.

Type I and III Interferon in the Gut: Tight Balance between Host Protection and Immunopathology

The intestinal mucosa forms an active interface to the outside word, facilitating nutrient and water uptake and at the same time acts as a barrier toward the highly colonized intestinal lumen. A tight balance of the mucosal immune system is essential to tolerate harmless antigens derived from food or commensals and to effectively defend against potentially dangerous pathogens. Interferons (IFN) provide a first line of host defense when cells detect an invading organism. Whereas type I IFN were discovered almost 60 years ago, type III IFN were only identified in the early 2000s. It was initially thought that type I IFN and type III IFN performed largely redundant functions. However, it is becoming increasingly clear that type III IFN exert distinct and non-redundant functions compared to type I IFN, especially in mucosal tissues. Here, we review recent progress made in unraveling the role of type I/III IFN in intestinal mucosal tissue in the steady state, in response to mucosal pathogens and during inflammation.

Mucosal Ecological Network of Epithelium and Immune Cells for Gut Homeostasis and Tissue Healing

The intestinal epithelial barrier includes columnar epithelial, Paneth, goblet, enteroendocrine, and tuft cells as well as other cell populations, all of which contribute properties essential for gastrointestinal homeostasis. The intestinal mucosa is covered by mucin, which contains antimicrobial peptides and secretory IgA and prevents luminal bacteria, fungi, and viruses from stimulating intestinal immune responses. Conversely, the transport of luminal microorganisms-mediated by M, dendritic, and goblet cells-into intestinal tissues facilitates the harmonization of active and quiescent mucosal immune responses. The bacterial population within gut-associated lymphoid tissues creates the intratissue cohabitations for harmonized mucosal immunity. Intermolecular and intercellular communication among epithelial, immune, and mesenchymal cells creates an environment conducive for epithelial regeneration and mucosal healing. This review summarizes the so-called intestinal mucosal ecological network-the complex but vital molecular and cellular interactions of epithelial mesenchymal cells, immune cells, and commensal microbiota that achieve intestinal homeostasis, regeneration, and healing.

P, Emiliano J. R, Amaro R. G, Briones S. L. High fat diet induces alterations to intraepithelial lymphocyte and cytokine mRNA in the small intestine of C57BL/6 mice

The aim of this work was to investigate the possible effect of high fat diet (HFD) induced obesity on iIEL subsets and their cytokine mRNA levels in C57BL/6 mice.

IL-17A-producing resident memory γδ T cells orchestrate the innate immune response to secondary oral Listeria monocytogenes infection

Memory γδ T cells are important for the clearance of Listeria monocytogenes infection in the intestinal mucosa. However, the mechanisms by which memory γδ T cells provide protection against secondary oral infection are poorly understood. Here we used a recombinant strain of L. monocytogenes that efficiently invades the intestinal epithelium to show that Vγ4(+) memory γδ T cells represent a resident memory (Trm) population in the mesenteric lymph nodes (MLNs). The γδ Trm exhibited a remarkably static pattern of migration that radically changed following secondary oral L. monocytogenes infection. The γδ Trms produced IL-17A early after rechallenge and formed organized clusters with myeloid cells surrounding L. monocytogenes replication foci only after a secondary oral infection. Antibody blocking studies showed that in addition to IL-17A, the chemokine receptor C-X-C chemokine receptor 3 (CXCR3) is also important to enable the local redistribution of γδ Trm cells and myeloid cells specifically near the sites of L. monocytogenes replication within the MLN to restrict bacterial growth and spread. Our findings support a role for γδ Trms in orchestrating protective immune responses against intestinal pathogens.

Patients with genetically heterogeneous synchronous colorectal cancer carry rare damaging germline mutations in immune-related genes

Synchronous colorectal cancers (syCRCs) are physically separated tumours that develop simultaneously. To understand how the genetic and environmental background influences the development of multiple tumours, here we conduct a comparative analysis of 20 syCRCs from 10 patients. We show that syCRCs have independent genetic origins, acquire dissimilar somatic alterations, and have different clone composition. This inter- and intratumour heterogeneity must be considered in the selection of therapy and in the monitoring of resistance. SyCRC patients show a higher occurrence of inherited damaging mutations in immune-related genes compared to patients with solitary colorectal cancer and to healthy individuals from the 1,000 Genomes Project. Moreover, they have a different composition of immune cell populations in tumour and normal mucosa, and transcriptional differences in immune-related biological processes. This suggests an environmental field effect that promotes multiple tumours likely in the background of inflammation.

Some individuals present with multiple synchronous colorectal tumours, but the genetic understanding of this is unclear. Here, the authors use a sequencing strategy to show that the synchronous tumours are genetically independent and the patients harbour rare germline damaging mutations in genes associated with the immune system.

Immune evasion of porcine enteric coronaviruses and viral modulation of antiviral innate signaling

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Enteric coronaviruses have evolved to modulate the host innate immunity.

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Viral IFN antagonists have been identified and they are mostly redundant.

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For protection of intestinal epithelia from enteric viruses, type III IFN plays a major role.

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are emerged and reemerging viruses in pigs, and together with transmissible gastroenteritis virus (TGEV), pose significant economic concerns to the swine industry. These viruses infect epithelial cells of the small intestine and cause watery diarrhea, dehydration, and a high mortality in neonatal piglets. Type I interferons (IFN-α/β) are major antiviral cytokines forming host innate immunity, and in turn, these enteric coronaviruses have evolved to modulate the host innate immune signaling during infection. Accumulating evidence however suggests that IFN induction and signaling in the intestinal epithelial cells differ from other epithelial cells, largely due to distinct features of the gut epithelial mucosal surface and commensal microflora, and it appears that type III interferon (IFN-λ) plays a key role to maintain the antiviral state in the gut. This review describes the recent understanding on the immune evasion strategies of porcine enteric coronaviruses and the role of different types of IFNs for intestinal antiviral innate immunity.

Murine Butyrophilin-Like 1 and Btnl6 Form Heteromeric Complexes in Small Intestinal Epithelial Cells and Promote Proliferation of Local T Lymphocytes

To date, few molecular conduits mediating the cross-talk between intestinal epithelial cells and intraepithelial lymphocytes (IELs) have been described. We recently showed that butyrophilin-like (Btnl) 1 can attenuate the epithelial response to activated IELs, resulting in reduced production of proinflammatory mediators, such as IL-6 and CXCL1. We here report that like Btnl1, murine Btnl6 expression is primarily confined to the intestinal epithelium. Although Btnl1 can exist in a cell surface-expressed homomeric form, we found that it additionally forms heteromeric complexes with Btnl6, and that the engagement of Btnl1 is a prerequisite for surface expression of Btnl6 on intestinal epithelial cells. In an IEL-epithelial cell coculture system, enforced epithelial cell expression of Btnl1 significantly enhanced the proliferation of IELs in the absence of exogenous activation. The effect on proliferation was dependent on the presence of IL-2 or IL-15 and restricted to IELs upregulating CD25. In the γδ T-cell subset, the Btnl1-Btnl6 complex, but not Btnl1, specifically elevated the proliferation of IELs bearing the Vγ7Vδ4 receptor. Thus, our results show that murine epithelial cell-specific Btnl proteins can form intrafamily heterocomplexes and suggest that the interaction between Btnl proteins and IELs regulates the expansion of IELs in the intestinal mucosa.