Human Anti-fungal Th17 Immunity and Pathology Rely on Cross-Reactivity against Candida albicans

A Pilot Clinical Study on Post-Operative Recurrence Provides Biological Clues for a Role of Candida Yeasts and Fluconazole in Crohn's Disease

Background and aims: This study prompted by growing evidence of the relationship between the yeast Candida albicans and Crohn’s disease (CD) was intended to assess the effect of a 6-month course of the antifungal fluconazole (FCZ) on post-operative recurrence of CD. Methods: Mycological samples (mouth swabs and stools) and serum samples were collected from 28 CD patients randomized to receive either FCZ (n = 14) or placebo (n = 14) before surgical resection. Serological analysis focused on levels of calprotectin, anti-glycan antibodies, and antibody markers of C. albicans pathogenic transition. Levels of galectin-3 and mannose binding lectin (MBL) involved in C. albicans sensing and inflammation were also measured. Results: 1, 2, 3, and 6 months after surgery, endoscopy revealed recurrence in 5/12 (41.7%) patients in the FCZ group and 5/9 (55.6%) in the placebo group, the small cohort preventing any clinical conclusions. In both groups, surgery was followed by a marked decrease in C. albicans colonization and biomarkers of C. albicans pathogenic transition decreased to non-significant levels. Anti-glycan antibodies also decreased but remained significant for CD. Galectin-3 and calprotectin also decreased. Conversely, MBL levels, which inversely correlated with anti-C. albicans antibodies before surgery, remained stable. Building biostatistical multivariate models to analyze he changes in antibody and lectin levels revealed a significant relationship between C. albicans and CD. Conclusion: Several combinations of biomarkers of adaptive and innate immunity targeting C. albicans were predictive of CD recurrence after surgery, with area under the curves (AUCs) as high as 0.86. FCZ had a positive effect on biomarkers evolution. ClinicalTrials.gov ID: NCT02997059, 19 December 2016. University Hospital Lille, Ministry of Health, France. Effect of Fluconazole on the Levels of Anti-Saccharomyces cerevisiae Antibodies (ASCA) After Surgical Resection for Crohn’s Disease. Multicenter, Randomized, and Controlled in Two Parallel Groups Versus Placebo.

Bacterial-fungal interactions in the neonatal gut influence asthma outcomes later in life

Bacterial members of the infant gut microbiota and bacterial-derived short-chain fatty acids (SCFAs) have been shown to be protective against childhood asthma, but a role for the fungal microbiota in asthma etiology remains poorly defined. We recently reported an association between overgrowth of the yeast Pichia kudriavzevii in the gut microbiota of Ecuadorian infants and increased asthma risk. In the present study, we replicated these findings in Canadian infants and investigated a causal association between early life gut fungal dysbiosis and later allergic airway disease (AAD). In a mouse model, we demonstrate that overgrowth of P. kudriavzevii within the neonatal gut exacerbates features of type-2 and -17 inflammation during AAD later in life. We further show that P. kudriavzevii growth and adherence to gut epithelial cells are altered by SCFAs. Collectively, our results underscore the potential for leveraging inter-kingdom interactions when designing putative microbiota-based asthma therapeutics.

CF Fungal Disease in the Age of CFTR Modulators

Fungi are increasingly recognised to have a significant role in the progression of lung disease in Cystic fibrosis with Aspergillus fumigatus the most common fungus isolated during respiratory sampling. The emergence of novel CFTR modulators has, however, significantly changed the outlook of disease progression in CF. In this review we discuss what impact novel CFTR modulators will have on fungal lung disease and its management in CF. We discuss how CFTR modulators affect antifungal innate immunity and consider the impact of Ivacaftor on fungal disease in individuals with gating mutations. We further review the increasing complication of drug-drug interactions with concurrent use of azole antifungal medication and highlight key unknowns that require addressing to fully understand the impact of CFTR modulators on fungal disease.

Tripterygium wilfordii Polyglycoside Ameliorated TNBS-Induced Colitis in Rats via Regulating Th17/Treg Balance in Intestinal Mucosa

Purpose

To investigate the therapeutic effect of Tripterygium wilfordii polyglycoside (TWP), a derivative from a Chinese traditional herb, on 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis, in a model for inflammatory bowel disease (IBD) in rats.

Methods

TWP was administrated to Wistar rats during TNBS-induced colitis to determine its therapeutic effect on active inflammation using the Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR), flow cytometry, and Western blotting. Peripheral blood CD4⁺ T-cells were isolated from patients with ulcerative colitis (UC) and incubated with TWP to verify its immune regulation mechanism by qRT-PCR and flow cytometry.

Results

Intragastric administration of TWP attenuated the severity of intestinal inflammation in TNBS-induced rat colitis, characterized by decreased DAI, histopathological scores, and expression of IL-6, TNFα, IFNγ, and IL-17A in intestinal mucosa. Furthermore, TWP reduced IL-17A⁺CD4⁺ T-cells, while enhanced Foxp3⁺CD25⁺CD4⁺ T-cells in peripheral blood, mesenteric lymph nodes (MLN), and spleen in rat colitis. Downstream signaling including ROR-γt, STAT3, and HIF1α expression in intestinal mucosa were suppressed by TWP. In addition, incubation with TWP suppressed IL-17A⁺CD4⁺ T-cell differentiation, while it promoted Foxp3⁺CD25⁺CD4⁺ T-cell differentiation in CD4⁺ T-cells isolated from UC patients.

Conclusion

TWP successfully ameliorated experimental rat colitis via regulating innate immune responses as well as Th17/Treg balance in intestinal mucosa, peripheral blood, MLN, and spleen. Moreover, the differentiation of peripheral blood CD4⁺ T-cell isolated from patients with UC was modulated by TWP. TWP may act as an optional complementary and alternative medicine for IBD.

Measuring oxidation within LC3-associated phagosomes that optimizes MHC class II restricted antigen presentation

LC3-associated phagocytosis (LAP) uses components of the molecular machinery of macroautophagy and is involved in the presentation of extracellular antigens by Major Histocompatibility Complex (MHC) class II molecules. It is initiated by receptor-mediated phagocytosis and results in the formation of LAPosomes: single-membrane vesicles that are decorated with the macroautophagy protein LC3B. LAPosomes have been described to prolong antigen presentation in macrophages but the molecular mechanism of this process is just beginning to be understood. Known key regulators of LAPosome formation are Reactive Oxygen Species (ROS), which can modulate the pH and the oxidative state within LAPosomes. Here, we present two complementary methods to monitor oxidation in LAPosomes and to study its function in MHC class II restricted antigen presentation, both in primary human macrophages: (I) Coating the LAP-trigger zymosan with OxyBURST allows semi-quantitative assessment of oxidation levels within LAPosomes by confocal microscopy. (II) The co-culture of macrophages with CD4⁺T cells to assess the effects of LAP on Candida albicans antigen presentation by measuring IL-17A and IFN-γ secretion.

Crossing Kingdoms: How the Mycobiota and Fungal-Bacterial Interactions Impact Host Health and Disease

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria.

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria. However, research from this past decade has started to complete the picture by focusing on important but largely neglected constituents of the microbiota: fungi, viruses, and archaea. The community of commensal fungi, also called the mycobiota, interacts with commensal bacteria and the host. It is thus not surprising that changes in the mycobiota have significant impact on host health and are associated with pathological conditions such as inflammatory bowel disease (IBD). In this review we will give an overview of why the mycobiota is an important research area and different mycobiota research tools. We will specifically focus on distinguishing transient and actively colonizing fungi of the oral and gut mycobiota and their roles in health and disease. In addition to correlative and observational studies, we will discuss mechanistic studies on specific cross-kingdom interactions of fungi, bacteria, and the host.

Recent advances in understanding the Th1/Th2 effector choice

For over 35 years since Mosmann and Coffman proposed the seminal “type 1 T helper (Th1)/type 2 T helper (Th2)” hypothesis in 1986, the immunological community has appreciated that naïve CD4 T cells need to make important decisions upon their activation, namely to differentiate towards a Th1, Th2, Th17 (interleukin-17-producing T helper), follicular T helper (Tfh), or regulatory T cell (Treg) fate to orchestrate a variety of adaptive immune responses. The major molecular underpinnings of the Th1/Th2 effector fate choice had been initially characterized using excellent reductionist in vitro culture systems, through which the transcription factors T-bet and GATA3 were identified as the master regulators for the differentiation of Th1 and Th2 cells, respectively. However, Th1/Th2 cell differentiation and their cellular heterogeneity are usually determined by a combinatorial expression of multiple transcription factors, particularly in vivo, where dendritic cell (DC) and innate lymphoid cell (ILC) subsets can also influence T helper lineage choices. In addition, inflammatory cytokines that are capable of inducing Th17 cell differentiation are also found to be induced during typical Th1- or Th2-related immune responses, resulting in an alternative differentiation pathway, transiting from a Th17 cell phenotype towards Th1 or Th2 cells. In this review, we will discuss the recent advances in the field, focusing on some new players in the transcriptional network, contributions of DCs and ILCs, and alternative differentiation pathways towards understanding the Th1/Th2 effector choice in vivo.

Intestinal mycobiota in health and diseases: from a disrupted equilibrium to clinical opportunities

Bacteria, viruses, protozoa, and fungi establish a complex ecosystem in the gut. Like other microbiota, gut mycobiota plays an indispensable role in modulating intestinal physiology. Notably, the most striking characteristics of intestinal fungi are their extraintestinal functions. Here, we provide a comprehensive review of the importance of gut fungi in the regulation of intestinal, pulmonary, hepatic, renal, pancreatic, and brain functions, and we present possible opportunities for the application of gut mycobiota to alleviate/treat human diseases. Video Abstract.

Respiratory Mycoses in COPD and Bronchiectasis

Chronic obstructive pulmonary disease (COPD) and bronchiectasis represent chronic airway diseases associated with significant morbidity and mortality. Bacteria and viruses are commonly implicated in acute exacerbations; however the significance of fungi in these airways remains poorly defined. While COPD and bronchiectasis remain recognized risk factors for the occurrence of Aspergillus-associated disease including chronic and invasive aspergillosis, underlying mechanisms that lead to the progression from colonization to invasive disease remain uncertain. Nonetheless, advances in molecular technologies have improved our detection, identification and understanding of resident fungi characterizing these airways. Mycobiome sequencing has revealed the complex varied and myriad profile of airway fungi in COPD and bronchiectasis, including their association with disease presentation, progression, and mortality. In this review, we outline the emerging evidence for the clinical importance of fungi in COPD and bronchiectasis, available diagnostic modalities, mycobiome sequencing approaches and association with clinical outcomes.

Local farming of gut fungi protects against dangerous imports

Candida albicans is viewed as a harmless commensal in health and a dangerous parasite in disease. Recently in Cell, Doron et al. (2021) reveal that C. albicans in the gut additionally serves as a mutualist by provoking the immune system to generate far-reaching antibodies that defend against invasive fungal infections.

Maintaining homeostatic control of periodontal bone tissue

Alveolar bone is a unique osseous tissue due to the proximity of dental plaque biofilms. Periodontal health and homeostasis are mediated by a balanced host immune response to these polymicrobial biofilms. Dysbiotic shifts within dental plaque biofilms can drive a proinflammatory immune response state in the periodontal epithelial and gingival connective tissues, which leads to paracrine signaling to subjacent bone cells. Sustained chronic periodontal inflammation disrupts "coupled" osteoclast-osteoblast actions, which ultimately result in alveolar bone destruction. This chapter will provide an overview of alveolar bone physiology and will highlight why the oral microbiota is a critical regulator of alveolar bone remodeling. The ecology of dental plaque biofilms will be discussed in the context that periodontitis is a polymicrobial disruption of host homeostasis. The pathogenesis of periodontal bone loss will be explained from both a historical and current perspective, providing the opportunity to revisit the role of fibrosis in alveolar bone destruction. Periodontal immune cell interactions with bone cells will be reviewed based on our current understanding of osteoimmunological mechanisms influencing alveolar bone remodeling. Lastly, probiotic and prebiotic interventions in the oral microbiota will be evaluated as potential noninvasive therapies to support alveolar bone homeostasis and prevent periodontal bone loss.

Oxidation inhibits autophagy protein deconjugation from phagosomes to sustain MHC class II restricted antigen presentation

LC3-associated phagocytosis (LAP) contributes to a wide range of cellular processes and notably to immunity. The stabilization of phagosomes by the macroautophagy machinery in human macrophages can maintain antigen presentation on MHC class II molecules. However, the molecular mechanisms involved in the formation and maturation of the resulting LAPosomes are not completely understood. Here, we show that reactive oxygen species (ROS) produced by NADPH oxidase 2 (NOX2) stabilize LAPosomes by inhibiting LC3 deconjugation from the LAPosome cytosolic surface. NOX2 residing in the LAPosome membrane generates ROS to cause oxidative inactivation of the protease ATG4B, which otherwise releases LC3B from LAPosomes. An oxidation-insensitive ATG4B mutant compromises LAP and thereby impedes sustained MHC class II presentation of exogenous Candida albicans antigens. Redox regulation of ATG4B is thereby an important mechanism for maintaining LC3 decoration of LAPosomes to support antigen processing for MHC class II presentation.

Broadly reactive human CD4+ T cells against Enterobacteriaceae are found in the naïve repertoire and are clonally expanded in the memory repertoire

Enterobacteriaceae are a large family of Gram-negative bacteria that includes both commensals and opportunistic pathogens. The latter can cause severe nosocomial infections, with outbreaks of multi-antibiotics resistant strains, thus being a major public health threat. In this study, we report that Enterobacteriaceae-reactive memory Th cells were highly enriched in a CCR6+ CXCR3+ Th1*/17 cell subset and produced IFN-γ, IL-17A, and IL-22. This T cell subset was severely reduced in septic patients with K. pneumoniae bloodstream infection who also selectively lacked circulating K. pneumonie-reactive T cells. By combining heterologous antigenic stimulation, single cell cloning and TCR Vβ sequencing, we demonstrate that a large fraction of memory Th cell clones was broadly cross-reactive to several Enterobacteriaceae species. These cross-reactive Th cell clones were expanded in vivo and a large fraction of them recognized the conserved outer membrane protein A antigen. Interestingly, Enterobacteriaceae broadly cross-reactive T cells were also prominent among in vitro primed naïve T cells. Collectively, these data point to the existence of immunodominant T cell epitopes shared among different Enterobacteriaceae species and targeted by cross-reactive T cells that are readily found in the pre-immune repertoire and are clonally expanded in the memory repertoire.

Tissue-resident memory Th17 cells maintain stable fungal commensalism in the oral mucosa

Keeping a stable equilibrium between the host and commensal microbes to which we are constantly exposed, poses a major challenge for the immune system. The host mechanisms that regulate homeostasis of the microbiota to prevent infection and inflammatory disorders are not fully understood. Here, we provide evidence that CD4+ tissue-resident memory T (TRM) cells act as central players in this process. Using a murine model of C. albicans commensalism we show that IL-17 producing CD69+CD103+CD4+ memory T cells persist in the colonized tissue long-term and independently of circulatory supplies. Consistent with the requirement of Th17 cells for limiting fungal growth, IL-17-producing TRM cells in the mucosa were sufficient to maintain prolonged colonization, while circulatory T cells were dispensable. Although TRM cells were first proposed to protect from pathogens causing recurrent acute infections, our results support a central function of TRM cells in the maintenance of commensalism.

Effects of Intestinal Fungi and Viruses on Immune Responses and Inflammatory Bowel Diseases

The intestinal microbiota comprises diverse fungal and viral components, in addition to bacteria. These microbes interact with the immune system and affect human physiology. Advances in metagenomics have associated inflammatory and autoimmune diseases with alterations in fungal and viral species in the gut. Studies of animal models have found that commensal fungi and viruses can activate host-protective immune pathways related to epithelial barrier integrity, but can also induce reactions that contribute to events associated with inflammatory bowel disease. Changes in our environment associated with modernization and the COVID-19 pandemic have exposed humans to new fungi and viruses, with unknown consequences. We review the lessons learned from studies of animal viruses and fungi commonly detected in the human gut and how these might affect health and intestinal disease.

Human gut mycobiota tune immunity via CARD9-dependent induction of anti-fungal IgG antibodies

Antibodies mediate natural and vaccine-induced immunity against viral and bacterial pathogens, whereas fungi represent a widespread kingdom of pathogenic species for which neither vaccine nor neutralizing antibody therapies are clinically available. Here, using a multi-kingdom antibody profiling (multiKAP) approach, we explore the human antibody repertoires against gut commensal fungi (mycobiota). We identify species preferentially targeted by systemic antibodies in humans, with Candida albicans being the major inducer of antifungal immunoglobulin G (IgG). Fungal colonization of the gut induces germinal center (GC)-dependent B cell expansion in extraintestinal lymphoid tissues and generates systemic antibodies that confer protection against disseminated C. albicans or C. auris infection. Antifungal IgG production depends on the innate immunity regulator CARD9 and CARD9+CX3CR1+ macrophages. In individuals with invasive candidiasis, loss-of-function mutations in CARD9 are associated with impaired antifungal IgG responses. These results reveal an important role of gut commensal fungi in shaping the human antibody repertoire through CARD9-dependent induction of host-protective antifungal IgG.

Microbiota as Drivers and as Therapeutic Targets in Ocular and Tissue Specific Autoimmunity

Autoimmune uveitis is a major cause of blindness in humans. Activation of retina-specific autoreactive T cells by commensal microbiota has been shown to trigger uveitis in mice. Although a culprit microbe and/or its immunogenic antigen remains to be identified, studies from inducible and spontaneous mouse models suggest the potential of microbiota-modulating therapies for treating ocular autoimmune disease. In this review, we summarize recent findings on the contribution of microbiota to T cell-driven, tissue-specific autoimmunity, with an emphasis on autoimmune uveitis, and analyze microbiota-altering interventions, including antibiotics, probiotics, and microbiota-derived metabolites (e.g., short-chain fatty acids), which have been shown to be effective in other autoimmune diseases. We also discuss the need to explore more translational animal models as well as to integrate various datasets (microbiomic, transcriptomic, proteomic, metabolomic, and other cellular measurements) to gain a better understanding of how microbiota can directly or indirectly modulate the immune system and contribute to the onset of disease. It is hoped that deeper understanding of these interactions may lead to more effective treatment interventions.

Fecal Fungal Dysbiosis in Chinese Patients With Alzheimer's Disease

Gut bacterial dysbiosis plays a vital role in the development of Alzheimer’s disease (AD). However, our understanding of alterations to the gut fungal microbiota and their correlations with host immunity in AD is still limited. Samples were obtained from 88 Chinese patients with AD, and 65 age- and gender-matched, cognitively normal controls. Using these samples, we investigated the fungal microbiota targeting internal transcribed spacer 2 (ITS2) rRNA genes using MiSeq sequencing, and analyzed their associations with the host immune response. Our data demonstrated unaltered fungal diversity but altered taxonomic composition of the fecal fungal microbiota in the AD patients. The analysis of the fungal microbiota was performed using 6,585,557 high-quality reads (2,932,482 reads from the controls and 3,653,075 from the AD patients), with an average of 43,042 reads per sample. We found that several key differential fungi such as Candida tropicalis and Schizophyllum commune were enriched in the AD patients, while Rhodotorula mucilaginosa decreased significantly. Interestingly, C. tropicalis and S. commune were positively correlated with IP-10 and TNF-α levels. In contrast, C. tropicalis was negatively correlated with IL-8 and IFN-γ levels, and R. mucilaginosa was negatively correlated with TNF-α level. PiCRUSt analysis revealed that lipoic acid metabolism, starch and sucrose metabolism were significantly decreased in the AD fungal microbiota. This study is the first to demonstrate fecal fungal dysbiosis in stable AD patients at a deeper level, and to identify the key differential fungi involved in regulating host systemic immunity. The analysis of the fungal microbiota in AD performed here may provide novel insights into the etiopathogenesis of AD and pave the way for improved diagnosis and treatment of AD.

Severely ill COVID-19 patients display impaired exhaustion features in SARS-CoV-2-reactive CD8+ T cells

The molecular properties of CD8+ T cells that respond to SARS-CoV-2 infection are not fully known. Here, we report on the single-cell transcriptomes of >80,000 virus-reactive CD8+ T cells, obtained using a modified Antigen-Reactive T cell Enrichment (ARTE) assay, from 39 COVID-19 patients and 10 healthy subjects. COVID-19 patients segregated into two groups based on whether the dominant CD8+ T cell response to SARS-CoV-2 was 'exhausted' or not. SARS-CoV-2-reactive cells in the exhausted subset were increased in frequency and displayed lesser cytotoxicity and inflammatory features in COVID-19 patients with mild compared to severe illness. In contrast, SARS-CoV-2-reactive cells in the dominant non-exhausted subset from patients with severe disease showed enrichment of transcripts linked to co-stimulation, pro-survival NF-κB signaling, and anti-apoptotic pathways, suggesting the generation of robust CD8+ T cell memory responses in patients with severe COVID-19 illness. CD8+ T cells reactive to influenza and respiratory syncytial virus from healthy subjects displayed polyfunctional features and enhanced glycolysis. Cells with such features were largely absent in SARS-CoV-2-reactive cells from both COVID-19 patients and healthy controls non-exposed to SARS-CoV-2. Overall, our single-cell analysis revealed substantial diversity in the nature of CD8+ T cells responding to SARS-CoV-2.

Biomarkers for the Diagnosis of Allergic Bronchopulmonary Aspergillosis in Cystic Fibrosis: A Systematic Review and Meta-Analysis

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to Aspergillus fumigatus and impacts 10% of individuals with cystic fibrosis (CF). A diagnosis of ABPA is challenging to establish in CF owing to overlapping clinical and radiologic features with CF lung disease. Recent studies have identified blood tests, imaging, and other biomarkers that may be useful for diagnosis.

OBJECTIVE

To summarize biomarkers that can aid in the diagnosis of ABPA in CF patients and to quantify their diagnostic accuracy through meta-analysis.

METHODS

We searched MEDLINE, EMBASE, and the Cochrane Controlled Register of Trials and included studies that used a laboratory technique or imaging modality in CF patients diagnosed with ABPA. Pooled sensitivity and specificity were calculated using a hierarchical summary receiver operating characteristic model.

RESULTS

We identified 791 articles, of which 29 met our eligibility criteria and 9 were included in the meta-analysis. Hyperattenuating mucus on computed tomography (CT) scan (n = 3 studies; pooled sensitivity 62% and specificity 92%) and serum specific immunoglobulin E against recombinant Aspergillus funigatus antigens f4 (n = 6; 69%, 89%) and f6 (n = 6; 39%, 97%) demonstrated high specificity. Based on single studies, serum thymus and activation regulated chemokine (92%, 94%), stimulated basophil expression of CD203c (94%, 74%), the inverted mucoid impaction signal on magnetic resonance imaging (94%, 100%), and skin prick test with recombinant Aspergillus fumigatus f4 and/or f6 (100%, 100%) showed high sensitivity and specificity.

CONCLUSIONS

Recent studies have found promising biomarkers for diagnosing ABPA in CF. Further research is needed to improve our understanding of their utility in diagnosis and disease monitoring.

The microbiota in pneumonia: From protection to predisposition

Mucosal surfaces of the upper respiratory tract and gut are physiologically colonized with their own collection of microbes, the microbiota. The normal upper respiratory tract and gut microbiota protects against pneumonia by impeding colonization by potentially pathogenic bacteria and by regulating immune responses. However, antimicrobial therapy and critical care procedures perturb the microbiota, thus compromising its function and predisposing to lung infections (pneumonia). Interindividual variations and age-related alterations in the microbiota also affect vulnerability to pneumonia. We discuss how the healthy microbiota protects against pneumonia and how host factors and medical interventions alter the microbiota, thus influencing susceptibility to pneumonia.

The gut mycobiome: a novel player in chronic liver diseases

The human gut microbiome (bacteria, fungi, viruses, and archaea) is a complex and diverse ecosystem. It plays an important role in human health, but is involved in several intestinal and extraintestinal diseases. Most research to date has focused on the role of bacteria, while studies focusing on fungi (also referred to as "mycobiome" or "fungome") are still in its infancy. In this review, we focus on the existing literature available about the gut mycobiome with an emphasis on compositional mycobiome changes associated with liver diseases, the impact on pathogenesis of disease, and its potential use as therapeutic targets. We also provide insights into current methodologies of studying mycobiome, and we highlight the interkingdom interactions in the context of disease and how they affect health of the host. Herein, by focusing on the gut mycobiome, this review provides novel insights and directions for liver research.

A Perspective Of Intestinal Immune-Microbiome Interactions In Alcohol-Associated Liver Disease

Uncovering the intricacies of the gut microbiome and how it interacts with the host immune system has opened up pathways in the search for the treatment of disease conditions. Alcohol-associated liver disease is a major cause of death worldwide. Research has shed light on the breakdown of the protective gut barriers, translocation of gut microbes to the liver and inflammatory immune response to microbes all contributing to alcohol-associated liver disease. This knowledge has opened up avenues for alternative therapies to alleviate alcohol-associated liver disease based on the interaction of the commensal gut microbiome as a key player in the regulation of the immune response. This review describes the relevance of the intestinal immune system, the gut microbiota, and specialized and non-specialized intestinal cells in the regulation of intestinal homeostasis. It also reflects how these components are altered during alcohol-associated liver disease and discusses new approaches for potential future therapies in alcohol-associated liver disease.

Candida albicans and candidalysin in inflammatory disorders and cancer

As our understanding of mycology progresses, the impact of fungal microbes on human health has become increasingly evident. Candida albicans is a common commensal fungus that gives rise to local and systemic infections, particularly in immunocompromised patients where it can result in mortality. However, C. albicans has also been quietly linked with a variety of inflammatory disorders, to which it has traditionally been considered incidental; recent studies may now provide new aspects of these relationships for further consideration. This review provides a novel perspective on the impact of C. albicans and its peptide toxin, candidalysin, on human health, exploring their contributions to pathology within a variety of diseases.

Modulation of IL-17A and IFNγ by β2-adrenergic agonist terbutaline and inverse-agonist nebivolol, influence of ADRB2 polymorphisms

<abstract><sec> <title>Background</title> <p>Upon activation, helper T (Th) cells produce cytokines such as IL-17A and IFNγ, which may exacerbate inflammatory disease and disorders. Adrenergic drugs are emerging as immunomodulatory agents to treat pro-inflammatory diseases, but their function is not completely understood. Th Cells express the β2-adrenergic receptor (β2AR) that is encoded by <italic>ADRB2</italic>. Agonists of the β2AR decrease IFNγ but can increase IL-17A from Th cells. We compared a β2AR agonist to an inverse-agonist, and assessed the influence of <italic>ADRB2</italic> polymorphisms on IL-17A and IFNγ responses.</p> </sec><sec> <title>Methods</title> <p>Peripheral blood mononuclear cells (PBMCs) from venous blood of healthy human participants were cultured with T cell activators anti-CD3 and anti-CD28 antibodies. Terbutaline, a β2AR agonist or nebivolol, a β1AR antagonist and β2AR inverse-agonist, were added <italic>in vitro</italic>. Cytokines IL-17A and IFNγ were measured using enzyme-linked immunosorbent assay. Genomic <italic>ADRB2</italic> and its immediate upstream region were sequenced using Sanger's method. Cytokine response to drug was analyzed based on <italic>ADRB2</italic> polymorphisms.</p> </sec><sec> <title>Results</title> <p>Terbutaline consistently inhibited IFNγ from activated PBMC samples. In contrast, it increased IL-17A in PBMC homozygous for Gly16 codon of <italic>ADRB2</italic>. Nebivolol inhibited IL-17A and IFNγ from activated Th cells. When applied to activated-PBMCs, nebivolol inhibited IL-17A but did not significantly inhibit IFNγ although a trend was observed. The ability of nebivolol to inhibit IL-17A was attenuated by a β2AR-specific antagonist. Cellular proliferation and viability was not significantly changed by nebivolol. Nebivolol suppressed IL-17A in all of the samples regardless of <italic>ADRB2</italic> polymorphisms.</p> </sec><sec> <title>Conclusions</title> <p>This data demonstrates that terbutaline inhibited IFNγ, however, it increased IL-17A in samples with the common Gly16 polymorphism of <italic>ADRB2</italic>. Nebivolol inhibited IL-17A regardless of <italic>ADRB2</italic> polymorphisms. Thus, nebivolol is a strong candidate for treating inflammatory diseases or disorders where IL-17A exacerbates symptoms.</p> </sec></abstract>

Human mucosal-associated invariant T cells respond to Mucorales species in a MR1-dependent manner

Activation of mucosal-associated invariant T cells (MAIT cells) by certain bacteria, viruses, and yeast is well studied, but the activation potential of filamentous moulds from the order Mucorales is not known. Here, we show a rapid response of human MAIT cells against the Mucorales species Mucor circinelloides, Rhizopus arrhizus, and Rhizopus microsporus. This activation included upregulation of CD69 and degranulation marked by increased CD107a expression, while intracellular perforin and granzyme A expression were reduced. Furthermore, blocking of the antigen-presenting molecule major histocompatibility complex class I-related abrogated MAIT cell activation demonstrating a T cell receptor-dependent stimulation by Mucorales.

Low-Avidity CD4+ T Cell Responses to SARS-CoV-2 in Unexposed Individuals and Humans with Severe COVID-19

CD4+ T cells reactive against SARS-CoV-2 can be found in unexposed individuals, and these are suggested to arise in response to common cold coronavirus (CCCoV) infection. Here, we utilized SARS-CoV-2-reactive CD4+ T cell enrichment to examine the antigen avidity and clonality of these cells, as well as the relative contribution of CCCoV cross-reactivity. SARS-CoV-2-reactive CD4+ memory T cells were present in virtually all unexposed individuals examined, displaying low functional avidity and multiple, highly variable cross-reactivities that were not restricted to CCCoVs. SARS-CoV-2-reactive CD4+ T cells from COVID-19 patients lacked cross-reactivity to CCCoVs, irrespective of strong memory T cell responses against CCCoV in all donors analyzed. In severe but not mild COVID-19, SARS-CoV-2-specific T cells displayed low functional avidity and clonality, despite increased frequencies. Our findings identify low-avidity CD4+ T cell responses as a hallmark of severe COVID-19 and argue against a protective role for CCCoV-reactive T cells in SARS-CoV-2 infection.

Systems biology of host-Candida interactions: understanding how we shape each other

Candida albicans is both a member of the human mucosal microbiota and a common agent of invasive fungal disease. Systems biology approaches allow for analysis of the interactions between this fungus and its mammalian host. Framing these studies by considering how C. albicans and its host construct the niche the other occupies provides insight into how these interactions shape the ecosystems, behavior, and evolution of each organism. Here, we discuss recent work on multiscale systems biology approaches for examining C. albicans in relation to the host ecosystem to identify the emergent properties of the interactions and new variables that can be targeted for development of therapeutic strategies.

The Fungal Microbiome and Asthma

Asthma is a group of inflammatory conditions that compromises the airways of a continuously increasing number of people around the globe. Its complex etiology comprises both genetic and environmental aspects, with the intestinal and lung microbiomes emerging as newly implicated factors that can drive and aggravate asthma. Longitudinal infant cohort studies combined with mechanistic studies in animal models have identified microbial signatures causally associated with subsequent asthma risk. The recent inclusion of fungi in human microbiome surveys has revealed that microbiome signatures associated with asthma risk are not limited to bacteria, and that fungi are also implicated in asthma development in susceptible individuals. In this review, we examine the unique properties of human-associated and environmental fungi, which confer them the ability to influence immune development and allergic responses. The important contribution of fungi to asthma development and exacerbations prompts for their inclusion in current and future asthma studies in humans and animal models.

Imbalance of Regulatory and Cytotoxic SARS-CoV-2-Reactive CD4+ T Cells in COVID-19

The contribution of CD4+ T cells to protective or pathogenic immune responses to SARS-CoV-2 infection remains unknown. Here, we present single-cell transcriptomic analysis of >100,000 viral antigen-reactive CD4+ T cells from 40 COVID-19 patients. In hospitalized patients compared to non-hospitalized patients, we found increased proportions of cytotoxic follicular helper cells and cytotoxic T helper (TH) cells (CD4-CTLs) responding to SARS-CoV-2 and reduced proportion of SARS-CoV-2-reactive regulatory T cells (TREG). Importantly, in hospitalized COVID-19 patients, a strong cytotoxic TFH response was observed early in the illness, which correlated negatively with antibody levels to SARS-CoV-2 spike protein. Polyfunctional TH1 and TH17 cell subsets were underrepresented in the repertoire of SARS-CoV-2-reactive CD4+ T cells compared to influenza-reactive CD4+ T cells. Together, our analyses provide insights into the gene expression patterns of SARS-CoV-2-reactive CD4+ T cells in distinct disease severities.

Phenotyping of Adaptive Immune Responses in Inflammatory Diseases

Immunophenotyping on the molecular and cellular level is a central aspect for characterization of patients with inflammatory diseases, both to better understand disease etiopathogenesis and based on this to develop diagnostic and prognostic biomarkers which allow patient stratification and tailor-made treatment strategies. Technology-driven developments have considerably expanded the range of analysis tools. Especially the analysis of adaptive immune responses, often regarded as central though mostly poorly characterized disease drivers, is a major focus of personalized medicine. The identification of the disease-relevant antigens and characterization of corresponding antigen-specific lymphocytes in individual patients benefits significantly from recent developments in cytometry by sequencing and proteomics. The aim of this workshop was to identify the important developments for state-of-the-art immunophenotyping for clinical application and precision medicine. We focused here on recent key developments in analysis of antigen-specific lymphocytes, sequencing, and proteomics approaches, their relevance in precision medicine and the discussion of the major challenges and opportunities for the future.

Mycobiome changes in the vitreous of post fever retinitis patients

Fungi have been associated with various diseases of the eye like keratitis, uveitis and endophthalmitis. Despite this fact, fungal microbiome (mycobiome) studies compared to the bacterial microbiome studies have remained neglected. In the present study, using metagenomic sequencing, the mycobiomes of the vitreous of healthy control individuals (VC, n = 15) and individuals with post fever retinitis + non-PFR uveitis (PFR+, n = 9) were analysed and compared. The results indicated that Ascomycota was the most predominant phylum in both VC and PFR+ groups. Further, at the genera level it was observed that the abundance of 17 fungal genera were significantly different in post fever retinitis (PFR, n = 6) group compared to control group. Of these 17 genera, it was observed that 14 genera were relatively more abundant in PFR group and the remaining 3 genera in the VC group. Genus Saccharomyces, a commensal of the gut and skin, was predominantly present in the vitreous of both the cohorts, however it was significantly less abundant in PFR group. Further, significant increase in the genera that have a pathogenic interaction with the host were observed in PFR group. On the whole the mycobiome in both the groups differed significantly and formed two distinct clusters in the heatmap and Principal co-ordinate analysis. These results demonstrate significant changes in the mycobiome from the vitreous of post fever retinitis patients compared to healthy controls thus implying that dysbiotic changes in the fungal vitreous microbiome are associated with PFR.

Th2 Biased Immunity With Altered B Cell Profiles in Circulation of Patients With Sporotrichosis Caused by Sporothrix globosa

Sporotrichosis is a subcutaneous mycotic infection, and Sporothrixglobosa is one of the causative agents with a worldwide distribution, notably in Asia. However, the immune profile in human sporotrichosis caused by S. globosa still remains obscure. Here, we demonstrated enhanced Th2 response in circulation with significant increases in Th2 frequency, Th2/Tregs as well as IL-4 seretion in patients. Elevated IL-17A⁺Th17 percentage was accompanied with reduced IL-17A level in serum, which may imply a dysfunction of this CD4⁺T subset in S. globosa infection. In addition, Th2 percentage, the ratios of Th2/Tregs and Th17/Tregs were all raised in patients with fixed cutaneous form, while only Th2/Tregs displayed increment in lymphocutaneous form. Meanwhile, the percentage of double negative B cells was significantly increased and positively correlated with Th2 and Tregs in whole patients. Except naïve B cells, all memory B cells together with Th2 cells increased in patients with short duration (less than 6 months), which may suggest a collaboration of T cells with altered B cell profile in human sporotrichosis caused by S. globosa. In consistent with the changes of IFN-γ⁺Th1, IL-4⁺Th2 and IL-17A⁺Th17 in patients with short duration, the percentages of these effector T cells all expanded when cocultured with S. globosa yeast cells in vitro. These data shed light on the potential involvement of peripheral T and B cell immunity against this mycotic infection and indicated that different immune responses existed in different stages of sporotrichosis; meanwhile different immune profile may contribute to different clinical manifestations of this disease.

HLA-A29 and Birdshot Uveitis: Further Down the Rabbit Hole

HLA class I alleles constitute established risk factors for non-infectious uveitis and preemptive genotyping of HLA class I alleles is standard practice in the diagnostic work-up. The HLA-A29 serotype is indispensable to Birdshot Uveitis (BU) and renders this enigmatic eye condition a unique model to better understand how the antigen processing and presentation machinery contributes to non-infectious uveitis or chronic inflammatory conditions in general. This review will discuss salient points regarding the protein structure of HLA-A29 and how key amino acid positions impact the peptide binding preference and interaction with T cells. We discuss to what extent the risk genes ERAP1 and ERAP2 uniquely affect HLA-A29 and how the discovery of a HLA-A29-specific submotif may impact autoantigen discovery. We further provide a compelling argument to solve the long-standing question why BU only affects HLA-A29-positive individuals from Western-European ancestry by exploiting data from the 1000 Genomes Project. We combine novel insights from structural and immunopeptidomic studies and discuss the functional implications of genetic associations across the HLA class I antigen presentation pathway to refine the etiological basis of Birdshot Uveitis.

T-Cell Immune Surveillance in Allogenic Stem Cell Transplant Recipients: Are Whole Blood-Based Assays Ready to Challenge ELISPOT?

We compared the feasibility of 4 cytomegalovirus (CMV)- and Aspergillus-reactive T-cell immunoassay protocols in allogenic stem cell transplant recipients. While enzyme-linked immunospot performed best overall, logistically advantageous whole blood–based assays performed comparably in patients with less severe lymphocytopenia. CMV-induced interferon-gamma responses correlated strongly across all protocols and showed high concordance with serology.

Microbial modulation of intestinal T helper cell responses and implications for disease and therapy

Induction of intestinal T helper cell subsets by commensal members of the intestinal microbiota is an important component of the many immune adaptations required to establish host-microbial homeostasis. Importantly, altered intestinal T helper cell profiles can have pathological consequences that are not limited to intestinal sites. Therefore, microbial-mediated modulation of the intestinal T helper cell profile could have strong therapeutic potentials. However, in order to develop microbial therapies that specifically induce the desired alterations in the intestinal T helper cell compartment one has to first gain a detailed understanding of how microbial composition and the metabolites derived or induced by the microbiota impact on intestinal T helper cell responses. Here we summarize the milestone findings in the field of microbiota-intestinal T helper cell crosstalk with a focus on the role of specific commensal bacteria and their metabolites. We discuss mechanistic mouse studies and are linking these to human studies where possible. Moreover, we highlight recent advances in the field of microbial CD4 T cell epitope mimicry in autoimmune diseases and the role of microbially-induced CD4 T cells in cancer immune checkpoint blockade therapy.

CD4 T Helper Cell Subsets and Related Human Immunological Disorders

The immune system plays a critical role in protecting hosts from the invasion of organisms. CD4 T cells, as a key component of the immune system, are central in orchestrating adaptive immune responses. After decades of investigation, five major CD4 T helper cell (Th) subsets have been identified: Th1, Th2, Th17, Treg (T regulatory), and Tfh (follicular T helper) cells. Th1 cells, defined by the expression of lineage cytokine interferon (IFN)-γ and the master transcription factor T-bet, participate in type 1 immune responses to intracellular pathogens such as mycobacterial species and viruses; Th2 cells, defined by the expression of lineage cytokines interleukin (IL)-4/IL-5/IL-13 and the master transcription factor GAΤA3, participate in type 2 immune responses to larger extracellular pathogens such as helminths; Th17 cells, defined by the expression of lineage cytokines IL-17/IL-22 and the master transcription factor RORγt, participate in type 3 immune responses to extracellular pathogens including some bacteria and fungi; Tfh cells, by producing IL-21 and expressing Bcl6, help B cells produce corresponding antibodies; whereas Foxp3-expressing Treg cells, unlike Th1/Th2/Th17/Tfh exerting their effector functions, regulate immune responses to maintain immune cell homeostasis and prevent immunopathology. Interestingly, innate lymphoid cells (ILCs) have been found to mimic the functions of three major effector CD4 T helper subsets (Th1, Th2, and Th17) and thus can also be divided into three major subsets: ILC1s, ILC2s, and ILC3s. In this review, we will discuss the differentiation and functions of each CD4 T helper cell subset in the context of ILCs and human diseases associated with the dysregulation of these lymphocyte subsets particularly caused by monogenic mutations.

T cell immunity to commensal fungi

Fungi are an important part of the microbiota in healthy barrier tissues. Fungal dysbiosis in turn is associated with local and distal inflammatory diseases. Recent advances have shed light on the antigen-specific IL-17-dependent mechanisms that regulate fungal commensalism and prevent fungal overgrowth during homeostasis. Progress in our understanding of species-specific differences in fungus-host interactions provides new hypotheses of why Candida albicans-targeting T cells exceed those directed against other fungal species in the human T cell repertoire. Importantly, C. albicans-specific Th17 cells can also contribute to immune pathology in distant organs such as the lung via cross-reaction with heterologous antigens.

Regulatory T cells for minimising immune suppression in kidney transplantation: phase I/IIa clinical trial

OBJECTIVE

To assess whether reshaping of the immune balance by infusion of autologous natural regulatory T cells (nTregs) in patients after kidney transplantation is safe, feasible, and enables the tapering of lifelong high dose immunosuppression, with its limited efficacy, adverse effects, and high direct and indirect costs, along with addressing several key challenges of nTreg treatment, such as easy and robust manufacturing, danger of over immunosuppression, interaction with standard care drugs, and functional stability in an inflammatory environment in a useful proof-of-concept disease model.

DESIGN

Investigator initiated, monocentre, nTreg dose escalation, phase I/IIa clinical trial (ONEnTreg13).

SETTING

Charité-University Hospital, Berlin, Germany, within the ONE study consortium (funded by the European Union).

PARTICIPANTS

Recipients of living donor kidney transplant (ONEnTreg13, n=11) and corresponding reference group trial (ONErgt11-CHA, n=9).

INTERVENTIONS

CD4+ CD25+ FoxP3+ nTreg products were given seven days after kidney transplantation as one intravenous dose of 0.5, 1.0, or 2.5-3.0×10⁶ cells/kg body weight, with subsequent stepwise tapering of triple immunosuppression to low dose tacrolimus monotherapy until week 48.

MAIN OUTCOME MEASURES

The primary clinical and safety endpoints were assessed by a composite endpoint at week 60 with further three year follow-up. The assessment included incidence of biopsy confirmed acute rejection, assessment of nTreg infusion related adverse effects, and signs of over immunosuppression. Secondary endpoints addressed allograft functions. Accompanying research included a comprehensive exploratory biomarker portfolio.

RESULTS

For all patients, nTreg products with sufficient yield, purity, and functionality could be generated from 40-50 mL of peripheral blood taken two weeks before kidney transplantation. None of the three nTreg dose escalation groups had dose limiting toxicity. The nTreg and reference groups had 100% three year allograft survival and similar clinical and safety profiles. Stable monotherapy immunosuppression was achieved in eight of 11 (73%) patients receiving nTregs, while the reference group remained on standard dual or triple drug immunosuppression (P=0.002). Mechanistically, the activation of conventional T cells was reduced and nTregs shifted in vivo from a polyclonal to an oligoclonal T cell receptor repertoire.

CONCLUSIONS

The application of autologous nTregs was safe and feasible even in patients who had a kidney transplant and were immunosuppressed. These results warrant further evaluation of Treg efficacy and serve as the basis for the development of next generation nTreg approaches in transplantation and any immunopathologies.

TRIAL REGISTRATION

NCT02371434 (ONEnTreg13) and EudraCT:2011-004301-24 (ONErgt11).

Analyzing the Mycobacterium tuberculosis immune response by T-cell receptor clustering with GLIPH2 and genome-wide antigen screening

CD4+ T cells are critical to fighting pathogens, but a comprehensive analysis of human T-cell specificities is hindered by the diversity of HLA alleles (>20,000) and the complexity of many pathogen genomes. We previously described GLIPH, an algorithm to cluster T-cell receptors (TCRs) that recognize the same epitope and to predict their HLA restriction, but this method loses efficiency and accuracy when >10,000 TCRs are analyzed. Here we describe an improved algorithm, GLIPH2, that can process millions of TCR sequences. We used GLIPH2 to analyze 19,044 unique TCRβ sequences from 58 individuals latently infected with Mycobacterium tuberculosis (Mtb) and to group them according to their specificity. To identify the epitopes targeted by clusters of Mtb-specific T cells, we carried out a screen of 3,724 distinct proteins covering 95% of Mtb protein-coding genes using artificial antigen-presenting cells (aAPCs) and reporter T cells. We found that at least five PPE (Pro-Pro-Glu) proteins are targets for T-cell recognition in Mtb.

Monocytes as Potential Mediators of Pathogen-Induced T-Helper 17 Differentiation in Patients With Primary Sclerosing Cholangitis (PSC)

BACKGROUND AND AIMS

T cells from patients with primary sclerosing cholangitis (PSC) show a prominent interleukin (IL)-17 response upon stimulation with bacteria or fungi, yet the reasons for this dominant T-helper 17 (Th17) response in PSC are not clear. Here, we analyzed the potential role of monocytes in microbial recognition and in skewing the T-cell response toward Th17.

APPROACH AND RESULTS

Monocytes and T cells from blood and livers of PSC patients and controls were analyzed ex vivo and in vitro using transwell experiments with cholangiocytes. Cytokine production was measured using flow cytometry, enzyme-linked immunosorbent assay, RNA in situ hybridization, and quantitative real-time PCR. Genetic polymorphisms were obtained from ImmunoChip analysis. Following ex vivo stimulation with phorbol myristate acetate/ionomycin, PSC patients showed significantly increased numbers of IL-17A-producing peripheral blood CD4⁺ T cells compared to PBC patients and healthy controls, indicating increased Th17 differentiation in vivo. Upon stimulation with microbes, monocytes from PSC patients produced significantly more IL-1β and IL-6, cytokines known to drive Th17 cell differentiation. Moreover, microbe-activated monocytes induced the secretion of Th17 and monocyte-recruiting chemokines chemokine (C-C motif) ligand (CCL)-20 and CCL-2 in human primary cholangiocytes. In livers of patients with PSC cirrhosis, CD14^hiCD16^int and CD14^loCD16^hi monocytes/macrophages were increased compared to alcoholic cirrhosis, and monocytes were found to be located around bile ducts.

CONCLUSIONS

PSC patients show increased Th17 differentiation already in vivo. Microbe-stimulated monocytes drive Th17 differentiation in vitro and induce cholangiocytes to produce chemokines mediating recruitment of Th17 cells and more monocytes into portal tracts. Taken together, these results point to a pathogenic role of monocytes in patients with PSC.

Fungal Infections Associated With the Use of Novel Immunotherapeutic Agents

Purpose of the Review

Recent concerns have emerged regarding the potential of immunotherapy to cause infection. In this review, we summarize the current literature on invasive fungal infections that occur during treatment with immune checkpoint inhibitors and chimeric antigen receptor T cell therapy.

Recent Findings

Fungal infections are uncommon with the use of checkpoint inhibitors. Most cases are caused by invasive aspergillosis and pneumocystis pneumonia and occur in patients requiring high dose corticosteroids for the management of immune-related adverse events. Conversely, fungal infections are commonly reported during therapy with CAR T cells. Most cases are caused by invasive aspergillosis and candidiasis and are likely the result of prolonged neutropenia following the conditioning regimen or immunosuppressant use for the management of cytokine release syndrome and neurotoxicity.

Summary

Treatment-related toxicities that require prolonged immunosuppressive agents appear to play a key role in the development of fungal infections during immunotherapy. Ongoing surveillance is needed to fully address the risks of fungal infections with these novel agents.

Gut microecology: Why our microbes could be key to our health

The human body contains a large number of microorganisms, and the gut microecology environment contains the largest number and types of microorganisms. The structure and function of gut microbiota are closely related to the health of the human body. In a cascade of studies, the diversity of gut microbiota and its metabolite often found changed in patients or mice model. What kind of gut microbiota that associated with the occurrence or treatment of diseases were also found in many studies. Gut microbiota and its products can affect the function of the human body. Short-chain fatty acids, bile acid, indoles and so on were found can regulate the inflammation, immune response to affect the process of diseases. Immune cells like natural killer T cells, CD3 + T cells were also found had a link to gut microbiota which associated with diseases. Changes in gut microbiota are associated with changes in the body's major systems, such as the digestive system, the endocrine system, the cardiovascular system, the endocrine and metabolic system, the urinary system diseases, the respiratory system and so on. It is of great significance to study gut microecology for the prevention and treatment of various human diseases.

Early life microbial exposures and allergy risks: opportunities for prevention

Allergies, including asthma, food allergy and atopic dermatitis, are increasing in prevalence, particularly in westernized countries. Although a detailed mechanistic explanation for this increase is lacking, recent evidence indicates that, in addition to genetic predisposition, lifestyle changes owing to modernization have an important role. Such changes include increased rates of birth by caesarean delivery, increased early use of antibiotics, a westernized diet and the associated development of obesity, and changes in indoor and outdoor lifestyle and activity patterns. Most of these factors directly and indirectly impact the formation of a diverse microbiota, which includes bacterial, viral and fungal components; the microbiota has a leading role in shaping (early) immune responses. This default programme is markedly disturbed under the influence of environmental and lifestyle risk factors. Here, we review the most important allergy risk factors associated with changes in our exposure to the microbial world and the application of this knowledge to allergy prevention strategies.

Could cross-reactivity rescue Foxp3+ regulatory T cell precursors from thymic deletion?

Thymocytes that bind with high affinity to peptides displayed by MHC class II (pMHC-II) are deleted while low-affinity binders differentiate into naive CD4+ T cells. However, Foxp3+ regulatory T cells (Tregs) seem to defy this binary choice as their precursors require high-affinity interaction with pMHC-II for maturation in the thymus. Here, we rely on the antigen-specific interpretive framework, SPIRAL (Specific ImmunoRegulatory Algorithm), to propose that Tregs escape thymic deletion by forming dyads with IL-2-producing T cells via antigen cross-reactivity. This interpretation reconciles contradictions related to Treg ontogeny in the thymus and their role in modulating antigen-specific immune responses.

Pathogen-induced tissue-resident memory TH17 (TRM17) cells amplify autoimmune kidney disease

Although it is well established that microbial infections predispose to autoimmune diseases, the underlying mechanisms remain poorly understood. After infection, tissue-resident memory T (T_RM) cells persist in peripheral organs and provide immune protection against reinfection. However, whether T_RM cells participate in responses unrelated to the primary infection, such as autoimmune inflammation, is unknown. By using high-dimensional single-cell analysis, we identified CD4⁺ T_RM cells with a T_H17 signature (termed T_RM17 cells) in kidneys of patients with ANCA-associated glomerulonephritis. Experimental models demonstrated that renal T_RM17 cells were induced by pathogens infecting the kidney, such as Staphylococcus aureus, Candida albicans, and uropathogenic Escherichia coli, and persisted after the clearance of infections. Upon induction of experimental glomerulonephritis, these kidney T_RM17 cells rapidly responded to local proinflammatory cytokines by producing IL-17A and thereby exacerbate renal pathology. Thus, our data show that pathogen-induced T_RM17 cells have a previously unrecognized function in aggravating autoimmune disease.

The gut, the bad and the harmless: Candida albicans as a commensal and opportunistic pathogen in the intestine

Candida albicans is a regular member of the intestinal microbiota in the majority of the human population. This underscores C. albicans' adaptation to life in the intestine without inducing competitive interactions with other microbes, or immune responses detrimental to its survival. However, specific conditions such as a dysbalanced microbiome, a suppression of the immune system, and an impaired intestinal barrier can predispose for invasive, mostly nosocomial, C. albicans infections. Colonization of the intestine and translocation through the intestinal barrier are fundamental aspects of the processes preceding life-threatening systemic candidiasis. Insights into C. albicans' commensal lifestyle and translocation can thus help us to understand how patients develop candidiasis, and may provide leads for therapeutic strategies aimed at preventing infection. In this review, we discuss the commensal lifestyle of C. albicans in the intestine, the role of morphology for commensalism, the influence of diet, and the interactions with bacteria of the microbiota.

Anti-fungal T cell responses in the lung and modulation by the gut-lung axis

The lung is a central organ for immune-environmental interactions ranging from tolerance against harmless substances to protection against pathogens, which are particularly sensitive to regulation by the intestinal microbiota. Airborne fungi, can cause variety of diseases, including allergies and inflammatory disorders, as well as life-threatening invasive infections. Remarkable differences exist between ubiquitous fungal species with regard to protective immune mechanisms. Recent data have surprisingly identified Aspergillus-specific regulatory T cells as an essential tolerance checkpoint and provided mechanistic insight for the loss of tolerance in the course of immune pathologies. Furthermore, pathogenic Th17 cells in Aspergillus-associated inflammatory disease seem to be induced by cross-reactivity to the intestinal commensal Candida albicans. Here we review and discuss what is known about fungus-specific T cell responses in the lung how they are modulated by the gut-lung axis and in particular discussing the modulation of adaptive immune responses by cross-reactivity to the microbiota.

Interleukin-17 cytokines: Effectors and targets in psoriasis-A breakthrough in understanding and treatment

This review summarizes the steps from basic research on IL-17 family cytokines to understanding their role in psoriasis pathogenesis to the approval of a number of monoclonal antibodies targeting IL-17 pathways as first line treatment of psoriasis and psoriatic arthritis.

The IL-17 cytokine family comprising IL-17A to IL-17F and receptor subunits IL-17RA to IL-17RE represents a genetically ancient intercellular network regulating local tissue homeostasis. Its pivotal role in antifungal defense and its central position in the pathogenesis of inflammatory diseases including psoriasis were discovered only relatively late in the early 2000s. Since the connection of dysregulated IL-17 and psoriasis pathogenesis turned out to be particularly evident, a number of monoclonal antibodies targeting IL-17 pathways have been approved and are used as first line treatment of moderate-to-severe plaque psoriasis and psoriatic arthritis, and further agents are currently in clinical development.