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

The metabolic sensor LKB1 regulates ILC3 homeostasis and mitochondrial function

Group 3 innate lymphoid cells (ILC3s) are tissue-resident cells that sense environmental cues, control infections, and promote tissue homeostasis at mucosal surfaces. The metabolic sensor liver kinase B1 (LKB1) integrates intracellular stress, metabolism, and mitochondrial function to promote the development and effector functions of a variety of immune cells; however, the role of LKB1 in ILC3 function was unknown. Here, we show that LKB1 is crucial for adult ILC3 homeostasis, cytokine production, and mitochondrial function. ILC3-specific LKB1 deletion resulted in a reduced number of ILC3s and interleukin-22 (IL-22) production. LKB1-deficient ILC3s had decreased survival, mitochondrial dysfunction, cytoplasmic lipid accumulation, and altered bioenergetics. Using LKB1 downstream kinase modulators, we found that LKB1 regulation of ILC3 survival and IL-22 production requires signaling through microtubule affinity-regulating kinases (MARKs). Mechanistically, LKB1 deficiency resulted in increased reactive oxygen species (ROS) production and NFAT2 and PD-1 expression. Our work reveals that metabolic regulation of enteric ILC3 function by an LKB1-dependent signaling network is crucial for intestinal immunity and tissue homeostasis.

Rebalancing immune homeostasis in combating disease: The impact of medicine food homology plants and gut microbiome

BACKGROUND

Gut microbiota plays an important role in multiple human physiological processes and an imbalance in it, including the species, abundance, and metabolites can lead to diseases. These enteric microorganisms modulate immune homeostasis by presenting a myriad of antigenic determinants and microbial metabolites. Medicinal and food homologous (MFH) plants, edible herbal materials for both medicine and food, are important parts of Traditional Chinese Medicine (TCM). MFH plants have drawn much attention due to their strong biological activity and low toxicity. However, the interplay of MFH and gut microbiota in rebalancing the immune homeostasis in combating diseases needs systematic illumination.

PURPOSE

The review discusses the interaction between MFH and gut microbiota, including the effect of MFH on the major group of gut microbiota and the metabolic effect of gut microbiota on MFH. Moreover, how gut microbiota influences the immune system in terms of innate and adaptive immunity is addressed. Finally, the immunoregulatory mechanisms of MFH in regulation of host pathophysiology via gut microbiota are summarized.

METHODS

Literature was searched, analyzed, and collected using databases, including PubMed, Web of Science, and Google Scholar using relevant keywords. The obtained articles were screened and summarized by the research content of MFH and gut microbiota in immune regulation.

RESULTS

The review demonstrates the interaction between MFH and gut microbiota in disease prevention and treatment. Not only do the intestinal microorganisms and intestinal mucosa constitute an important immune barrier of the human body, but also lymphoid tissue and diffused immune cells within the mucosa participate in the response of innate immunity and adaptive immunity. MFH modulates immune regulation by affecting intestinal flora, helps maintain the balance of the immune system and interfere with the occurrence and development of a broad category of diseases.

CONCLUSION

Being absorbed from the gastrointestinal tract, MFH can have profound effects on gut microbiota. In turn, the gut microbiota also actively participate in the bioconversion of complex constituents from MFH, which could further influence their physiological and pharmacological properties. The review deepens the understanding of the relationship among MFH, gut microbiota, immune system, and human diseases and further promotes the progression of additional relevant research.

GPX4 restricts ferroptosis of NKp46+ILC3s to control intestinal inflammation

Group 3 innate lymphoid cells (ILC3s) are essential for both pathogen defense and tissue homeostasis in the intestine. Dysfunction of ILC3s could lead to increased susceptibility to intestinal inflammation. However, the precise mechanisms governing the maintenance of intestinal ILC3s are yet to be fully elucidated. Here, we demonstrated that ferroptosis is vital for regulating the survival of intestinal ILC3. Ferroptosis-related genes, including GPX4, a key regulator of ferroptosis, were found to be upregulated in intestinal mucosal ILC3s from ulcerative colitis patients. Deletion of GPX4 resulted in a decrease in NKp46+ILC3 cell numbers, impaired production of IL-22 and IL-17A, and exacerbated intestinal inflammation in a T cell-independent manner. Our mechanistic studies revealed that GPX4-mediated ferroptosis in NKp46+ILC3 cells was regulated by the LCN2-p38-ATF4-xCT signaling pathway. Mice lacking LCN2 in ILC3s or administration of a p38 pathway inhibitor exhibited similar phenotypes of ILC3 and colitis to those observed in GPX4 conditional knock-out mice. These observations provide novel insights into therapeutic strategies for intestinal inflammation by modulating ILC3 ferroptosis.

Antibody Fc-receptor FcεR1γ stabilizes cell surface receptors in group 3 innate lymphoid cells and promotes anti-infection immunity

Group 3 innate lymphoid cells (ILC3) are crucial for maintaining mucosal homeostasis and regulating inflammatory diseases, but the molecular mechanisms governing their phenotype and function are not fully understood. Here, we show that ILC3s highly express Fcer1g gene, which encodes the antibody Fc-receptor common gamma chain, FcεR1γ. Genetic perturbation of FcεR1γ leads to the absence of critical cell membrane receptors NKp46 and CD16 in ILC3s. Alanine scanning mutagenesis identifies two residues in FcεR1γ that stabilize its binding partners. FcεR1γ expression in ILC3s is essential for effective protective immunity against bacterial and fungal infections. Mechanistically, FcεR1γ influences the transcriptional state and proinflammatory cytokine production of ILC3s, relying on the CD16-FcεR1γ signaling pathway. In summary, our findings highlight the significance of FcεR1γ as an adapter protein that stabilizes cell membrane partners in ILC3s and promotes anti-infection immunity.

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.

Efficient enzyme-free method to assess the development and maturation of the innate and adaptive immune systems in the mouse colon

Researchers who aim to globally analyze the gastrointestinal immune system via flow cytometry have many protocol options to choose from, with specifics generally tied to gut wall layers of interest. To get a clearer idea of the approach we should use on full-thickness colon samples from mice, we first undertook a systematic comparison of three tissue dissociation techniques: two based on enzymatic cocktails and the other one based on manual crushing. Using flow cytometry panels of general markers of lymphoid and myeloid cells, we found that the presence of cell-surface markers and relative cell population frequencies were more stable with the mechanical method. Both enzymatic approaches were associated with a marked decrease of several cell-surface markers. Using mechanical dissociation, we then developed two minimally overlapping panels, consisting of a total of 26 antibodies, for serial profiling of lymphoid and myeloid lineages from the mouse colon in greater detail. Here, we highlight how we accurately delineate these populations by manual gating, as well as the reproducibility of our panels on mouse spleen and whole blood. As a proof-of-principle of the usefulness of our general approach, we also report segment- and life stage-specific patterns of immune cell profiles in the colon. Overall, our data indicate that mechanical dissociation is more suitable and efficient than enzymatic methods for recovering immune cells from all colon layers at once. Additionally, our panels will provide researchers with a relatively simple tool for detailed immune cell profiling in the murine gastrointestinal tract, regardless of life stage or experimental conditions.

Group 3 innate lymphoid cells: A trained Gutkeeper

Group 3 innate lymphoid cells (ILC3s) are tissue-resident immune lymphocytes that critically regulate intestinal homeostasis, organogenesis, and immunity. ILC3s possess the capacity to "sense" the inflammatory environment within tissues, especially in the context of pathogen challenges that imprints durable non-antigen-specific changes in ILC3 function. As such, ILC3s become a new actor in the emerging field of trained innate immunity. Here, we summarize recent discoveries regarding ILC3 responses to bacterial challenges and the role these encounters play in triggering trained innate immunity. We further discuss how signaling events throughout ILC3 ontogeny potentially control the development and function of trained ILC3s. Finally, we highlight the open questions surrounding ILC3 "training" the answers to which may reveal new insights into innate immunity. Understanding the fundamental concepts behind trained innate immunity could potentially lead to the development of new strategies for improving immunity-based modulation therapies for inflammation, infectious diseases, and cancer.

Serotonin Transporter Deficiency Induces Metabolic Alterations in the Ileal Mucosa

Serotonin transporter (SERT) deficiency has been implicated in metabolic syndrome, intestinal inflammation, and microbial dysbiosis. Interestingly, changes in microbiome metabolic capacity and several alterations in host gene expression, including lipid metabolism, were previously observed in SERT-/- mice ileal mucosa. However, the precise host or microbial metabolites altered by SERT deficiency that may contribute to the pleiotropic phenotype of SERT KO mice are not yet understood. This study investigated the hypothesis that SERT deficiency impacts lipid and microbial metabolite abundances in the ileal mucosa, where SERT is highly expressed. Ileal mucosal metabolomics was performed by Metabolon on wild-type (WT) and homozygous SERT knockout (KO) mice. Fluorescent-activated cell sorting (FACS) was utilized to measure immune cell populations in ileal lamina propria to assess immunomodulatory effects caused by SERT deficiency. SERT KO mice exhibited a unique ileal mucosal metabolomic signature, with the most differentially altered metabolites being lipids. Such changes included increased diacylglycerols and decreased monoacylglycerols in the ileal mucosa of SERT KO mice compared to WT mice. Further, the ileal mucosa of SERT KO mice exhibited several changes in microbial-related metabolites known to play roles in intestinal inflammation and insulin resistance. SERT KO mice also had a significant reduction in the abundance of ileal group 3 innate lymphoid cells (ILC3). In conclusion, SERT deficiency induces complex alterations in the ileal mucosal environment, indicating potential links between serotonergic signaling, gut microbiota, mucosal immunity, intestinal inflammation, and metabolic syndrome.

IL-18-induced HIF-1α in ILC3s ameliorates the inflammation of C. rodentium-induced colitis

Group 3 innate lymphoid cells (ILC3s) are vital for defending tissue barriers from invading pathogens. Hypoxia influences the production of intestinal ILC3-derived cytokines by activating HIF. Yet, the mechanisms governing HIF-1α in ILC3s and other innate RORγt+ cells during in vivo infections are poorly understood. In our study, transgenic mice with specific Hif-1a gene inactivation in innate RORγt+ cells (RAG1KO HIF-1α▵Rorc) exhibit more severe colitis following Citrobacter rodentium infection, primarily due to the inability to upregulate IL-22. We find that HIF-1α▵Rorc mice have impaired IL-22 production in ILC3s, while non-ILC3 innate RORγt+ cells, also capable of producing IL-22, remain unaffected. Furthermore, we show that IL-18, induced by Toll-like receptor 2, selectively triggers IL-22 in ILC3s by transcriptionally upregulating HIF-1α, revealing an oxygen-independent regulatory pathway. Our results highlight that, during late-stage C. rodentium infection, IL-18 induction in the colon promotes IL-22 through HIF-1α in ILC3s, which is crucial for protection against this pathogen.

On the path to predicting immune responses in the lung: Modeling the pulmonary innate immune system at the air-liquid interface (ALI)

Chronic respiratory diseases and infections are among the largest contributors to death globally, many of which still have no cure, including chronic obstructive pulmonary disorder, idiopathic pulmonary fibrosis, and respiratory syncytial virus among others. Pulmonary therapeutics afford untapped potential for treating lung infection and disease through direct delivery to the site of action. However, the ability to innovate new therapeutic paradigms for respiratory diseases will rely on modeling the human lung microenvironment and including key cellular interactions that drive disease. One key feature of the lung microenvironment is the air-liquid interface (ALI). ALI interface modeling techniques, using cell-culture inserts, organoids, microfluidics, and precision lung slices (PCLS), are rapidly developing; however, one major component of these models is lacking-innate immune cell populations. Macrophages, neutrophils, and dendritic cells, among others, represent key lung cell populations, acting as the first responders during lung infection or injury. Innate immune cells respond to and modulate stromal cells and bridge the gap between the innate and adaptive immune system, controlling the bodies response to foreign pathogens and debris. In this article, we review the current state of ALI culture systems with a focus on innate immune cells and suggest ways to build on current models to add complexity and relevant immune cell populations.

ILC3: a case of conflicted identity

Innate lymphoid cells type 3 (ILC3s) are the first line sentinels at the mucous tissues, where they contribute to the homeostatic immune response in a major way. Also, they have been increasingly appreciated as important modulators of chronic inflammatory and autoimmune responses, both locally and systemically. The proper identification of ILC3 is of utmost importance for meaningful studies on their role in immunity. Flow cytometry is the method of choice for the detection and characterization of ILC3. However, the analysis of ILC3-related papers shows inconsistency in ILC3 phenotypic definition, as different inclusion and exclusion markers are used for their identification. Here, we present these discrepancies in the phenotypic characterization of human and mouse ILC3s. We discuss the pros and cons of using various markers for ILC3 identification. Furthermore, we consider the possibilities for the efficient isolation and propagation of ILC3 from different organs and tissues for in-vitro and in-vivo studies. This paper calls upon uniformity in ILC3 definition, isolation, and propagation for the increased possibility of confluent interpretation of ILC3's role in immunity.

FOXO1 orchestrates the intestinal homeostasis via neuronal signaling in group 3 innate lymphoid cells

The neuro-immune regulation is associated with homeostasis of the intestine. Intestinal group 3 innate lymphoid cells (ILC3s) are tissue-resident lymphocytes whose functions are affected by the intestine niche. However, how a gut neuronal signal coordinates the immune response of ILC3s is largely unknown. Here, we found that cyclic adenosine monophosphate (cAMP) signaling exacerbated the inflammatory response and attenuated the expression level of the transcription factor forkhead box O1 (FOXO1) in ILC3s. Deficiency of FOXO1 drove the hyperactivation of ILC3s and resulted in gut inflammation independently of T cells. Mechanistically, FOXO1 promoted the transcription of neuropeptide receptor VIPR2 and inhibited the transcription of adrenoceptor ADRA2A in ILC3s. FOXO1-related regulation of VIPR2 and ADRA2A signaling balanced the activation of ILC3s under steady condition or during colitis. Moreover, chronic stress elevated cAMP level and downregulated FOXO1 level, exacerbating intestinal inflammation. Our findings reveal that FOXO1 balances the activation of ILC3s via VIP and adrenergic signaling and regulates intestinal homeostasis.

Lactobacillus reuteri in digestive system diseases: focus on clinical trials and mechanisms

Objectives

Digestive system diseases have evolved into a growing global burden without sufficient therapeutic measures. Lactobacillus reuteri (L. reuteri) is considered as a new potential economical therapy for its probiotic effects in the gastrointestinal system. We have provided an overview of the researches supporting various L. reuteri strains' application in treating common digestive system diseases, including infantile colic, diarrhea, constipation, functional abdominal pain, Helicobacter pylori infection, inflammatory bowel disease, diverticulitis, colorectal cancer and liver diseases.

Methods

The summarized literature in this review was derived from databases including PubMed, Web of Science, and Google Scholar.

Results

The therapeutic effects of L. reuteri in digestive system diseases may depend on various direct and indirect mechanisms, including metabolite production as well as modulation of the intestinal microbiome, preservation of the gut barrier function, and regulation of the host immune system. These actions are largely strain-specific and depend on the activation or inhibition of various certain signal pathways. It is well evidenced that L. reuteri can be effective both as a prophylactic measure and as a preferred therapy for infantile colic, and it can also be recommended as an adjuvant strategy to diarrhea, constipation, Helicobacter pylori infection in therapeutic settings. While preclinical studies have shown the probiotic potential of L. reuteri in the management of functional abdominal pain, inflammatory bowel disease, diverticulitis, colorectal cancer and liver diseases, its application in these disease settings still needs further study.

Conclusion

This review focuses on the probiotic effects of L. reuteri on gut homeostasis via certain signaling pathways, and emphasizes the importance of these probiotics as a prospective treatment against several digestive system diseases.

Limosilactobacillus reuteri in immunomodulation: molecular mechanisms and potential applications

Frequent use of hormones and drugs may be associated with side-effects. Recent studies have shown that probiotics have effects on the prevention and treatment of immune-related diseases. Limosilactobacillus reuteri (L. reuteri) had regulatory effects on intestinal microbiota, host epithelial cells, immune cells, cytokines, antibodies (Ab), toll-like receptors (TLRs), tryptophan (Try) metabolism, antioxidant enzymes, and expression of related genes, and exhibits antibacterial and anti-inflammatory effects, leading to alleviation of disease symptoms. Although the specific composition of the cell-free supernatant (CFS) of L. reuteri has not been clarified, its efficacy in animal models has drawn increased attention to its potential use. This review summarizes the effects of L. reuteri on intestinal flora and immune regulation, and discusses the feasibility of its application in atopic dermatitis (AD), asthma, necrotizing enterocolitis (NEC), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS), and provides insights for the prevention and treatment of immune-related diseases.

Modulation of innate lymphoid cells by enteric bacterial pathogens

Innate lymphoid cells (ILCs) are key regulators of tissue homeostasis, inflammation, and immunity to infections. ILCs rapidly respond to environmental cues such as cytokines, microbiota and invading pathogens which regulate their function and phenotype. Even though ILCs are rare cells, they are enriched at barrier surfaces such as the gastrointestinal (GI) tract, and they are often critical to the host's immune response to eliminate pathogens. On the other side of host-pathogen interactions, pathogenic bacteria also have the means to modulate these immune responses. Manipulation or evasion of the immune cells is often to the pathogen's benefit and/or to the detriment of competing microbiota. In some instances, specific bacterial virulence factors or toxins have been implicated in how the pathogen modulates immunity. In this review, we discuss the recent progress made towards understanding the role of non-cytotoxic ILCs during enteric bacterial infections, how these pathogens can modulate the immune response, and the implications these have on developing new therapies to combat infection.

Impact of aging on immunity in the context of COVID-19, HIV, and tuberculosis

Knowledge of aging biology needs to be expanded due to the continuously growing number of elderly people worldwide. Aging induces changes that affect all systems of the body. The risk of cardiovascular disease and cancer increases with age. In particular, the age-induced adaptation of the immune system causes a greater susceptibility to infections and contributes to the inability to control pathogen growth and immune-mediated tissue damage. Since the impact of aging on immune function, is still to be fully elucidated, this review addresses some of the recent understanding of age-related changes affecting key components of immunity. The emphasis is on immunosenescence and inflammaging that are impacted by common infectious diseases that are characterized by a high mortality, and includes COVID-19, HIV and tuberculosis.

Potential Role of Innate Lymphoid Cells in the Pathogenesis and Treatment of Skin Diseases

Group 2 innate lymphoid cells (ILC2s) are lymphoid cells that are resident in mucosal tissues, especially the skin, which, once stimulated by epithelial cell-derived cytokines, release IL-5, IL-13, and IL-4, as the effectors of type 2 immune responses. This research aims to evaluate the role of ILC2s in the pathogenesis of skin diseases, with a particular focus on inflammatory cutaneous disorders, in order to also elucidate potential therapeutic perspectives. The research has been conducted in articles, excluding reviews and meta-analyses, on both animals and humans. The results showed that ILC2s play a crucial role in the pathogenesis of systemic skin manifestations, prognosis, and severity, while a potential antimelanoma role is emerging from the new research. Future perspectives could include the development of new antibodies targeting or stimulating ILC2 release. This evidence could add a new therapeutic approach to inflammatory cutaneous conditions, including allergic ones.

Context-Dependent Regulation of Type17 Immunity by Microbiota at the Intestinal Barrier

T-helper-17 (Th17) cells and related IL-17-producing (type17) lymphocytes are abundant at the epithelial barrier. In response to bacterial and fungal infection, the signature cytokines IL-17A/F and IL-22 mediate the antimicrobial immune response and contribute to wound healing of injured tissues. Despite their protective function, type17 lymphocytes are also responsible for various chronic inflammatory disorders, including inflammatory bowel disease (IBD) and colitis associated cancer (CAC). A deeper understanding of type17 regulatory mechanisms could ultimately lead to the discovery of therapeutic strategies for the treatment of chronic inflammatory disorders and the prevention of cancer. In this review, we discuss the current understanding of the development and function of type17 immune cells at the intestinal barrier, focusing on the impact of microbiota-immune interactions on intestinal barrier homeostasis and disease etiology.

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.

Notch, RORC and IL-23 signals cooperate to promote multi-lineage human innate lymphoid cell differentiation

Innate lymphoid cells (ILCs) include cytotoxic natural killer cells and distinct groups of cytokine-producing innate helper cells which participate in immune defense and promote tissue homeostasis. Circulating human ILC precursors (ILCP) able to generate all canonical ILC subsets via multi-potent or uni-potent intermediates according to our previous work. Here we show potential cooperative roles for the Notch and IL-23 signaling pathways for human ILC differentiation from blood ILCP using single cell cloning analyses and validate these findings in patient samples with rare genetic deficiencies in IL12RB1 and RORC. Mechanistically, Notch signaling promotes upregulation of the transcription factor RORC, enabling acquisition of Group 1 (IFN-γ) and Group 3 (IL-17A, IL-22) effector functions in multi-potent and uni-potent ILCP. Interfering with RORC or signaling through its target IL-23R compromises ILC3 effector functions but also generally suppresses ILC production from multi-potent ILCP. Our results identify a Notch->RORC- > IL-23R pathway which operates during human ILC differentiation. These observations may help guide protocols to expand functional ILC subsets in vitro with an aim towards novel ILC therapies for human disease.

Targeting Th17 cells in HIV-1 remission/cure interventions

Since the discovery of HIV-1, progress has been made in deciphering the viral replication cycle and mechanisms of host-pathogen interactions that has facilitated the implementation of effective antiretroviral therapies (ARTs). Major barriers to HIV-1 remission/cure include the persistence of viral reservoirs (VRs) in long-lived CD4⁺ T cells, residual viral transcription, and lack of mucosal immunity restoration during ART, which together fuel systemic inflammation. Recently, T helper (Th)17-polarized cells were identified as major contributors to the pool of transcriptionally/translationally competent VRs. In this review, we discuss the functional features of Th17 cells that were elucidated by fundamental immunology studies in the context of autoimmunity. We also highlight recent discoveries supporting the possibility of extrapolating this knowledge toward the identification of new putative Th17-targeted HIV-1 remission/cure strategies.

Microplastic consumption induces inflammatory signatures in the colon and prolongs a viral arthritis

Global microplastic (MP) contamination and the effects on the environment are well described. However, the potential for MP consumption to affect human health remains controversial. Mice consuming ≈80 μg/kg/day of 1 μm polystyrene MPs via their drinking water showed no weight loss, nor were MPs detected in internal organs. The microbiome was also not significantly changed. MP consumption did lead to small transcriptional changes in the colon suggesting plasma membrane perturbations and mild inflammation. Mice were challenged with the arthritogenic chikungunya virus, with MP consumption leading to a significantly prolonged arthritic foot swelling that was associated with elevated Th1, NK cell and neutrophil signatures. Immunohistochemistry also showed a significant increase in the ratio of neutrophils to monocyte/macrophages. The picture that emerges is reminiscent of enteropathic arthritis, whereby perturbations in the colon are thought to activate innate lymphoid cells that can inter alia migrate to joint tissues to promote inflammation.

Efficient In Vitro Generation of IL-22-Secreting ILC3 From CD34+ Hematopoietic Progenitors in a Human Mesenchymal Stem Cell Niche

Innate lymphoid cells (ILCs) and in particular ILC3s have been described to be vital for mucosal barrier functions and homeostasis within the gastrointestinal (GI) tract. Importantly, IL-22-secreting ILC3 have been implicated in the control of inflammatory bowel disease (IBD) and were shown to reduce the incidence of graft-versus-host disease (GvHD) as well as the risk of transplant rejection. Unfortunately, IL-22-secreting ILC3 are primarily located in mucosal tissues and are not found within the circulation, making access to them in humans challenging. On this account, there is a growing desire for clinically applicable protocols for in vitro generation of effector ILC3. Here, we present an approach for faithful generation of functionally competent human ILC3s from cord blood-derived CD34+ hematopoietic progenitors on layers of human mesenchymal stem cells (MSCs) generated in good manufacturing practice (GMP) quality. The in vitro-generated ILC3s phenotypically, functionally, and transcriptionally resemble bona fide tissue ILC3 with high expression of the transcription factors (TF) RorγT, AHR, and ID2, as well as the surface receptors CD117, CD56, and NKp44. Importantly, the majority of ILC3 belonged to the desired effector subtype with high IL-22 and low IL-17 production. The protocol thus combines the advantages of avoiding xenogeneic components, which were necessary in previous protocols, with a high propensity for generation of IL-22-producing ILC3. The present approach is suitable for the generation of large amounts of ILC3 in an all-human system, which could facilitate development of clinical strategies for ILC3-based therapy in inflammatory diseases and cancer.

Citrobacter rodentium Infection Induces Persistent Molecular Changes and Interferon Gamma-Dependent Major Histocompatibility Complex Class II Expression in the Colonic Epithelium

Most studies of infections at mucosal surfaces have focused on the acute phase of the disease. Consequently, little is known about the molecular processes that underpin tissue recovery and the long-term consequences postinfection. Here, we conducted temporal deep quantitative proteomic analysis of colonic intestinal epithelial cells (cIECs) from mice infected with the natural mouse pathogen Citrobacter rodentium over time points corresponding to the late steady-state phase (10 days postinfection [DPI]), the clearance phase (13 to 20 DPI), and 4 weeks after the pathogen has been cleared (48 DPI). C. rodentium, which relies on a type III secretion system to infect, is used to model infections with enteropathogenic and enterohemorrhagic Escherichia coli. We observe a strong upregulation of inflammatory signaling and nutritional immunity responses during the clearance phase of the infection. Despite morphological tissue recovery, chromogranin B (ChgB)-positive endocrine cells remained significantly below baseline levels at 48 DPI. In contrast, we observed an increased abundance of proteins involved in antigen processing and presentation 4 weeks after pathogen clearance. In particular, long-term changes were characterized by a persistent interferon gamma (IFN-γ) response and the expression of major histocompatibility complex class II (MHCII) molecules in 60% of the EpCAM⁺ cIECs, which were not seen in Ifnγ^-/- mice. Nonetheless, both wild-type and Ifnγ^-/- mice mounted similar systemic and colonic IgG responses to C. rodentium and were equally protected from rechallenge, suggesting that cIEC MHCII is not necessary for protective immunity against C. rodentium. IMPORTANCE Mucosal surfaces respond to infection by mounting an array of metabolic, inflammatory, and tissue repair responses. While these have been well studied during acute infection, less is known about tissue recovery after pathogen clearance. We employ the mouse pathogen Citrobacter rodentium, which binds colonic intestinal epithelial cells (cIECs), to investigate the long-term effects of bacterial infection on gut physiology. Using global proteomic analysis, we study cIEC temporal responses during and after the clearance phase of infection. While the overall tissue morphology recovered, cIECs showed persistent signs of infection 4 weeks after pathogen clearance. These were characterized by a strong IFN-γ signature, including the upregulation of major histocompatibility complex class II (MHCII) antigen presentation proteins, suggesting that the tissue remains on "high alert" for weeks after the acute insult is resolved. However, we demonstrate that cIEC MHCII expression, which is induced by IFN-γ, is not required for protective IgG-mediated immunity against C. rodentium; instead, it may play a role in mucosal recovery.