Innate lymphoid cells as regulators of immunity, inflammation and tissue homeostasis. Nat Immunol. 2016;17:765-774. [PMID: 27328006 DOI: 10.1038/ni.3489]

Role of the intestinal mucosa in acute gastrointestinal GVHD

Intestinal graft-versus-host disease (GVHD) remains a significant obstacle to the success of allogeneic hematopoietic cell transplantation. The intestinal mucosa comprises the inner lining of the intestinal tract and maintains close proximity with commensal microbes that reside within the intestinal lumen. Recent advances have significantly improved our understanding of the interactions between the intestinal mucosa and the enteric microbiota. Changes in host mucosal tissue and commensals posttransplant have been actively investigated, and provocative insights into mucosal immunity and the enteric microbiota are now being translated into clinical trials of novel approaches for preventing and treating acute GVHD. In this review, we summarize recent findings related to aspects of the intestinal mucosa during acute GVHD.

Food allergy: immune mechanisms, diagnosis and immunotherapy

Food allergy is a pathological, potentially deadly, immune reaction triggered by normally innocuous food protein antigens. The prevalence of food allergies is rising and the standard of care is not optimal, consisting of food-allergen avoidance and treatment of allergen-induced systemic reactions with adrenaline. Thus, accurate diagnosis, prevention and treatment are pressing needs, research into which has been catalysed by technological advances that are enabling a mechanistic understanding of food allergy at the cellular and molecular levels. We discuss the diagnosis and treatment of IgE-mediated food allergy in the context of the immune mechanisms associated with healthy tolerance to common foods, the inflammatory response underlying most food allergies, and immunotherapy-induced desensitization. We highlight promising research advances, therapeutic innovations and the challenges that remain.

Immune modules shared by innate lymphoid cells and T cells

In recent years, innate lymphoid cells (ILCs) have emerged as innate correlates to T cells. The similarities between ILCs and T cells indicate that lymphocytes of fundamentally distinct lineages can share core "immune modules" that encompass transcriptional circuitry and effector functions while using nonredundant complementary mechanisms of pattern recognition to enact these functions. We review modules currently recognized to be shared between ILCs and T cells.

Cellular and molecular regulation of innate inflammatory responses

Innate sensing of pathogens by pattern-recognition receptors (PRRs) plays essential roles in the innate discrimination between self and non-self components, leading to the generation of innate immune defense and inflammatory responses. The initiation, activation and resolution of innate inflammatory response are mediated by a complex network of interactions among the numerous cellular and molecular components of immune and non-immune system. While a controlled and beneficial innate inflammatory response is critical for the elimination of pathogens and maintenance of tissue homeostasis, dysregulated or sustained inflammation leads to pathological conditions such as chronic infection, inflammatory autoimmune diseases. In this review, we discuss some of the recent advances in our understanding of the cellular and molecular mechanisms for the establishment and regulation of innate immunity and inflammatory responses.

Combination of Adt-O1Manisa and Ad5-boIFNλ3 induces early protective immunity against foot-and-mouth disease in cattle

Foot-and-mouth-disease (FMD) remains the most infectious livestock disease worldwide. Although commercially available inactivated or adenovirus-vectored-vaccines (Ad5-FMD) are effective, they require 5-7 days to induce protection. Therefore, new control strategies that stimulate rapid immune responses are needed. Expression of bovine interferon λ3 using the Ad5-vector platform (Ad5-boIFNλ3) is able to delay disease in cattle, but clinical signs appear at 9 days after challenge. We hypothesized that combination of Ad5-boIFNλ3 and Ad5-FMD could induce immediate and lasting protection against FMD. Cattle were vaccinated with an Ad5-FMD, Ad5-boIFNλ3, or the combination of both, followed by challenge at three days post-immunization. All animals treated with Ad5-FMD combined with Ad5-boIFNλ3 were fully protected against FMD, despite the absence of systemic neutralizing antibodies or antiviral activity at the time of challenge. Induction of a strong cell-mediated immune response suggested that Ad5-boIFNλ3 is able to act as an adjuvant of Ad5-FMD vaccine in cattle.

Understanding Immune Cells in Tertiary Lymphoid Organ Development: It Is All Starting to Come Together

Tertiary lymphoid organs (TLOs) are frequently observed in tissues affected by non-resolving inflammation as a result of infection, autoimmunity, cancer, and allograft rejection. These highly ordered structures resemble the cellular composition of lymphoid follicles typically associated with the spleen and lymph node compartments. Although TLOs within tissues show varying degrees of organization, they frequently display evidence of segregated T and B cell zones, follicular dendritic cell networks, a supporting stromal reticulum, and high endothelial venules. In this respect, they mimic the activities of germinal centers and contribute to the local control of adaptive immune responses. Studies in various disease settings have described how these structures contribute to either beneficial or deleterious outcomes. While the development and architectural organization of TLOs within inflamed tissues requires homeostatic chemokines, lymphoid and inflammatory cytokines, and adhesion molecules, our understanding of the cells responsible for triggering these events is still evolving. Over the past 10–15 years, novel immune cell subsets have been discovered that have more recently been implicated in the control of TLO development and function. In this review, we will discuss the contribution of these cell types and consider the potential to develop new therapeutic strategies that target TLOs.

Effects of n-3 PUFAs on Intestinal Mucosa Innate Immunity and Intestinal Microbiota in Mice after Hemorrhagic Shock Resuscitation

n-3 polyunsaturated fatty acids (PUFAs) can improve the function of the intestinal barrier after damage from ischemia-reperfusion or hemorrhagic shock resuscitation (HSR). However, the effects of n-3 PUFAs on intestinal microbiota and the innate immunity of the intestinal mucosa after HSR remain unclear. In the present study, 40 C57BL/6J mice were randomly assigned to five groups: control, sham, HSR, HSR + n-3 PUFAs and HSR + n-6 PUFAs. Mice were sacrificed 12 h after HSR. Liver, spleen, mesenteric lymph nodes and terminal ileal tissues were collected. Intestinal mucosae were scraped aseptically. Compared with the HSR group, the number of goblet cells increased, expression of mucin 2 was restored and disturbed intestinal microbiota were partly stabilized in the PUFA-administered groups, indicating that both n-3 and n-6 PUFAs reduced overproliferation of Gammaproteobacteria while promoting the growth of Bacteroidetes. Notably, n-3 PUFAs had an advantage over n-6 PUFAs in improving ileal tissue levels of lysozyme after HSR. Thus, PUFAs, especially n-3 PUFAs, partly improved the innate immunity of intestinal mucosa in mice after HSR. These findings suggest a clinical rationale for providing n-3 PUFAs to patients recovering from ischemia-reperfusion.

Human innate lymphoid cells

Innate lymphoid cells (ILCs) are increasingly acknowledged as important mediators of immune homeostasis and pathology. ILCs act as early orchestrators of immunity, responding to epithelium-derived signals by expressing an array of cytokines and cell-surface receptors, which shape subsequent immune responses. As such, ILCs make up interesting therapeutic targets for several diseases. In patients with allergy and asthma, group 2 innate lymphoid cells produce high amounts of IL-5 and IL-13, thereby contributing to type 2-mediated inflammation. Group 3 innate lymphoid cells are implicated in intestinal homeostasis and psoriasis pathology through abundant IL-22 production, whereas group 1 innate lymphoid cells are accumulated in chronic inflammation of the gut (inflammatory bowel disease) and lung (chronic obstructive pulmonary disease), where they contribute to IFN-γ-mediated inflammation. Although the ontogeny of mouse ILCs is slowly unraveling, the development of human ILCs is far from understood. In addition, the growing complexity of the human ILC family in terms of previously unrecognized functional heterogeneity and plasticity has generated confusion within the field. Here we provide an updated view on the function and plasticity of human ILCs in tissue homeostasis and disease.

Evidence of innate lymphoid cell redundancy in humans

Innate lymphoid cells (ILCs) have potent immune functions in experimental conditions in mice, but their contribution to immunity in natural conditions in humans remains unclear. We investigated the presence of ILCs in a cohort of patients with severe combined immunodeficiency (SCID). All ILC subsets were absent in SCID patients carrying mutations of IL2RG or JAK3. T cell reconstitution was observed in SCID patients upon hematopoietic stem cell transplantation (HSCT), but the patients still exhibited drastic reduction of ILCs in the absence of myeloablation, at the exception of rare cases of ILC1 reconstitution. Remarkably, the observed ILC deficiencies were not associated with any particular susceptibility to disease, with a follow-up extending from 7 to 39 years after HSCT. We thus report here the first cases of selective ILC deficiency in humans, and show that ILCs may be dispensable in natural conditions, if T cells are present and B cell function is preserved.

Aryl hydrocarbon receptor signaling involves in the human intestinal ILC3/ILC1 conversion in the inflamed terminal ileum of Crohn's disease patients

Innate lymphoid cells (ILCs) are emerging as important components of our immune system that have critical effector and regulatory functions in both innate and adaptive immune responses. They are enriched at mucosal surfaces, such as lung and intestine. Our previous work has shown that Lineage⁻CRTH2⁻CD45⁺NKp44⁻CD117⁻CD127⁺ILC1s accumulated in the inflamed terminal ileum of patients with Crohn’s disease (CD) at the expense of NKp44⁺ILC3s. This phenotype conversion impairs the intestinal barrier integrity and contributes to the dysregulated immune responses of CD patients. Our next step was to search for pathways to modulate this phenotype switch. The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor. Initial studies of AHR concentrated on its role in the detoxification of xenobiotics. However, recent research has focused on the immune system. Especially, AHR pathway is proven to be essential for the maintenance of intestinal ILC3s in mouse models. We examined whether AHR pathway participated in the human intestinal ILC phenotype change in the inflamed terminal ileum of CD patients. As anticipated, NKp44⁺ILC3s, NKp44⁻ILC3s and ILC1s had differential AHR expression. This AHR signaling mediated CD117 expression on the surface of ILC3s. The conversion from ILC3 to ILC1 was accompanied by the downregulation of AHR expression. We further observed that there was a disparity between AHR protein expression and mRNA expression in the inflamed terminal ileum tissues of CD patients compared to unaffected areas. These findings suggest that AHR pathway is also important for human intestinal ILC phenotype regulation and impaired AHR signaling in the inflamed gut of CD patients possibly contributes to the ILC3/ILC1 conversion.