Dietary Derived Micronutrients Modulate Immune Responses Through Innate Lymphoid Cells

The role of the aryl hydrocarbon receptor (AhR) in modulating intestinal ILC3s to optimise gut pathogen resistance in lupus and benefits of nutritional AhR ligands

BACKGROUND AND AIMS

Dysbiosis is emerging as a potential trigger of systemic lupus erythematosus (SLE). Group 3 innate lymphoid cells (ILC3s) are recognised as key regulators of intestinal homeostasis. The aryl hydrocarbon receptor (AhR) is critical to intestinal ILC3 development and function. This mechanistic review aimed to investigate whether AhR activation of gut ILC3s facilitates IL-22-mediated antimicrobial peptide (AMP) production to enhance colonisation resistance and ameliorate SLE pathology associated with intestinal dysbiosis. Furthermore, nutritional AhR ligand potential to enhance pathogen resistance was explored.

METHODOLOGY

This mechanistic review involved a three-tranche systematic literature search (review, mechanism, intervention) using PubMed with critical appraisal. Data was synthesised into themes and summarised in a narrative analysis.

RESULTS

Preclinical mechanistic data indicate that AhR modulation of intestinal ILC3s optimises pathogen resistance via IL-22-derived AMPs. Pre-clinical research is required to validate this mechanism in SLE. Data on systemic immune consequences of AhR modulation in lupus suggest UVB-activated ligands induce aberrant AhR signalling while many dietary ligands exert beneficial effects. Data on xenobiotic-origin ligands is varied, although considerable evidence has demonstrated negative effects on Th17 to Treg balance. Limited human evidence supports the role of nutritional AhR ligands in modulating SLE pathology. Preclinical and clinical data support anti-inflammatory effects of dietary AhR ligands.

CONCLUSION

Current evidence is insufficient to fully validate the hypothesis that AhR modulation of intestinal ILC3s can enhance pathogen resistance to ameliorate lupus pathology driven by dysbiosis. However, anti-inflammatory effects of dietary AhR ligands suggest a promising role as a therapeutic intervention for SLE.

Emerging role of gut microbiota in autoimmune diseases

Accumulating studies have indicated that the gut microbiota plays a pivotal role in the onset of autoimmune diseases by engaging in complex interactions with the host. This review aims to provide a comprehensive overview of the existing literatures concerning the relationship between the gut microbiota and autoimmune diseases, shedding light on the complex interplay between the gut microbiota, the host and the immune system. Furthermore, we aim to summarize the impacts and potential mechanisms that underlie the interactions between the gut microbiota and the host in autoimmune diseases, primarily focusing on systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, type 1 diabetes mellitus, ulcerative colitis and psoriasis. The present review will emphasize the clinical significance and potential applications of interventions based on the gut microbiota as innovative adjunctive therapies for autoimmune diseases.

Effects of organic trace minerals chelated with oligosaccharides on growth performance, blood parameters, slaughter performance and meat quality in sheep

The present study assessed the effects of oligosaccharide-chelated organic trace minerals (OTM) on the growth performance, digestive enzyme activity, blood parameters, slaughter performance, and meat quality indexes of mutton sheep. A total of 60 East Ujumuqin × small-tailed Han crossbred mutton sheep were assigned to two groups (10 duplicates per group) by body weight (26.12 ± 3.22 kg) according to a completely randomized design. Compared to the CON group, the results of the OTM group showed: (1) no significant changes in the initial body weight, final body weight, dry matter intake, average daily gain, and feed conversion ratio (p > 0.05); (2) the activities of trypsin, lipase, and amylase in the jejunum were significantly increased (p < 0.05); (3) serum total protein, albumin, and globulin of the blood were significantly increased (p < 0.05), and the growth factor interleukin IL-10 was significantly higher (p < 0.05), while IL-2, IL-6, and γ-interferon were significantly lower (p < 0.05). Immunoglobulins A, M, and G were significantly higher (p < 0.05); (4) the live weight before slaughter, carcass weights, dressing percentage, eye muscle areas, and GR values did not differ significantly (p > 0.05); (5) shear force of mutton was significantly lower (p < 0.05), while the pH45min, pH24h, drip loss, and cooking loss did not show a significant difference (p > 0.05). The content of crude protein was significantly higher (p < 0.05), while the ether extract content was significantly reduced (p < 0.05), but no significant difference was detected between moisture and ash content; (6) the total amino acids, essential amino acids, semi-essential amino acids, and umami amino acids were significantly increased (p < 0.05). Although umami amino acids were not significant, the total volume increased (p > 0.05). Among these, the essential amino acids, threonine, valine, leucine, lysine in essential amino acids and arginine were significantly increased (p < 0.05). Also, non-essential amino acids, glycine, serine, proline, tyrosine, cysteine, and aspartic acid, were significantly higher (p < 0.05). The content of alanine, aspartate, glutamic acid, phenylalanine, and tyrosine in umami amino acids was significantly higher (p < 0.05).

Nutrition in chronic inflammatory conditions: Bypassing the mucosal block for micronutrients

Nutritional Immunity is one of the most ancient innate immune responses, during which the body can restrict nutrients availability to pathogens and restricts their uptake by the gut mucosa (mucosal block). Though this can be a beneficial strategy during infection, it also is associated with non-communicable diseases-where the pathogen is missing; leading to increased morbidity and mortality as micronutritional uptake and distribution in the body is hindered. Here, we discuss the acute immune response in respect to nutrients, the opposing nutritional demands of regulatory and inflammatory cells and particularly focus on some nutrients linked with inflammation such as iron, vitamins A, Bs, C, and other antioxidants. We propose that while the absorption of certain micronutrients is hindered during inflammation, the dietary lymph path remains available. As such, several clinical trials investigated the role of the lymphatic system during protein absorption, following a ketogenic diet and an increased intake of antioxidants, vitamins, and minerals, in reducing inflammation and ameliorating disease.

Amino acid availability acts as a metabolic rheostat to determine the magnitude of ILC2 responses

Group 2 innate lymphoid cells (ILC2) are functionally poised, tissue-resident lymphocytes that respond rapidly to damage and infection at mucosal barrier sites. ILC2 reside within complex microenvironments where they are subject to cues from both the diet and invading pathogens-including helminths. Emerging evidence suggests ILC2 are acutely sensitive not only to canonical activating signals but also perturbations in nutrient availability. In the context of helminth infection, we identify amino acid availability as a nutritional cue in regulating ILC2 responses. ILC2 are found to be uniquely preprimed to import amino acids via the large neutral amino acid transporters Slc7a5 and Slc7a8. Cell-intrinsic deletion of these transporters individually impaired ILC2 expansion, while concurrent loss of both transporters markedly impaired the proliferative and cytokine-producing capacity of ILC2. Mechanistically, amino acid uptake determined the magnitude of ILC2 responses in part via tuning of mTOR. These findings implicate essential amino acids as a metabolic requisite for optimal ILC2 responses within mucosal barrier tissues.

Lack of iron, zinc, and vitamins as a contributor to the etiology of atopic diseases

Micronutritional deficiencies are common in atopic children suffering from atopic dermatitis, food allergy, rhinitis, and asthma. A lack of iron, in particular, may impact immune activation with prolonged deficiencies of iron, zinc, vitamin A, and vitamin D associated with a Th2 signature, maturation of macrophages and dendritic cells (DCs), and the generation of IgE antibodies. In contrast, the sufficiency of these micronutrients establishes immune resilience, promotion of regulatory cells, and tolerance induction. As micronutritional deficiencies mimic an infection, the body's innate response is to limit access to these nutrients and also impede their dietary uptake. Here, we summarize our current understanding of the physiological function of iron, zinc, and vitamins A and D in relation to immune cells and the clinical consequences of deficiencies in these important nutrients, especially in the perinatal period. Improved dietary uptake of iron is achieved by vitamin C, vitamin A, and whey compounds, whereas zinc bioavailability improves through citrates and proteins. The addition of oil is essential for the dietary uptake of beta-carotene and vitamin D. As for vitamin D, the major source comes via sun exposure and only a small amount is consumed via diet, which should be factored into clinical nutritional studies. We summarize the prevalence of micronutritional deficiencies of iron, zinc, and vitamins in the pediatric population as well as nutritional intervention studies on atopic diseases with whole food, food components, and micronutrients. Dietary uptake via the lymphatic route seems promising and is associated with a lower atopy risk and symptom amelioration. This review provides useful information for clinical studies and concludes/emphasizes that a healthy, varied diet containing dairy products, fish, nuts, fruits, and vegetables as well as supplementing foods or supplementation with micronutrients as needed is essential to combat the atopic march.

Innate lymphoid cells: More than just immune cells

Since their discovery, innate lymphoid cells (ILCs) have been described as the innate counterpart of the T cells. Indeed, ILCs and T cells share many features including their common progenitors, transcriptional regulation, and effector cytokine secretion. Several studies have shown complementary and redundant roles for ILCs and T cells, leaving open questions regarding why these cells would have been evolutionarily conserved. It has become apparent in the last decade that ILCs, and rare immune cells more generally, that reside in non-lymphoid tissue have non-canonical functions for immune cells that contribute to tissue homeostasis and function. Viewed through this lens, ILCs would not be just the innate counterpart of T cells, but instead act as a link between sensory cells that monitor any changes in the environment that are not necessarily pathogenic and instruct effector cells that act to maintain body homeostasis. As these non-canonical functions of immune cells are operating in absence of pathogenic signals, it opens great avenues of research for immunologists that they now need to identify the physiological cues that regulate these cells and how the process confers a finer level of control and a greater flexibility that enables the organism to adapt to changing environmental conditions. In the review, we highlight how ILCs participate in the physiologic function of the tissue in which they reside and how physiological cues, in particular neural inputs control their homeostatic activity.

Circular RNA circTmem241 drives group III innate lymphoid cell differentiation via initiation of Elk3 transcription

Innate lymphoid cells (ILCs) exert important roles in host defense, tissue repair and inflammatory diseases. However, how ILC lineage specification is regulated remains largely elusive. Here we identify that circular RNA circTmem241 is highly expressed in group III innate lymphoid cells (ILC3s) and their progenitor cells. CircTmem241 deficiency impairs ILC3 commitment and attenuates anti-bacterial immunity. Mechanistically, circTmem241 interacts with Nono protein to recruit histone methyltransferase Ash1l onto Elk3 promoter in ILC progenitor cells (ILCPs). Ash1l-mediated histone modifications on Elk3 promoter enhance chromatin accessibility to initiate Elk3 transcription. Of note, circTmem241^-/-, Nono^-/- and Ash1l^-/- ILCPs display impaired ILC3 differentiation, while Elk3 overexpression rescues ILC3 commitment ability. Finally, circTmem241^-/-Elk3^-/- mice show lower numbers of ILC3s and are more susceptible to bacterial infection. We reveal that the circTmem241-Nono-Ash1l-Elk3 axis is required for the ILCP differentiation into ILC3P and ILC3 maturation, which is important to manipulate this axis for ILC development on treatment of infectious diseases.

Group 3 innate lymphoid cells mediate host defense against attaching and effacing pathogens

Group 3 innate lymphoid cells (ILC3) are innate effector cells that have essential roles in lymphoid organogenesis and maintenance of tissue homeostasis under steady-state and pathogenic conditions. ILC3 also promote immune defense, notably during bacterial breach of epithelial barriers, including those caused by attaching and effacing (A/E) pathogens for which Citrobacter rodentium infection in mice is a relevant pre-clinical model. Through their ability to sustain interactions with tissue-resident immune cells, epithelial cells, neurons or stromal cells, ILC3 constitute a key orchestrator that maintains the intestinal barrier. In this review, we will examine the function of murine ILC3 in host defense against C. rodentium infection and provide a discussion of recent advances that help elucidate the specific roles of these novel innate immune effector cells at mucosal surfaces.