Inflammatory ER stress responses dictate the immunopathogenic progression of systemic candidiasis

Recognition of pathogen-associated molecular patterns can trigger the inositol-requiring enzyme 1α (IRE1α) arm of the endoplasmic reticulum (ER) stress response in innate immune cells. This process maintains ER homeostasis and also coordinates diverse immunomodulatory programs during bacterial and viral infections. However, the role of innate IRE1α signaling in response to fungal pathogens remains elusive. Here, we report that systemic infection with the human opportunistic fungal pathogen Candida albicans induced proinflammatory IRE1α hyperactivation in myeloid cells that led to fatal kidney immunopathology. Mechanistically, simultaneous activation of the TLR/IL-1R adaptor protein MyD88 and the C-type lectin receptor dectin-1 by C. albicans induced NADPH oxidase-driven generation of ROS, which caused ER stress and IRE1a-dependent overexpression of key inflammatory mediators such as IL-1Β, IL-6, chemokine (C-C motif) ligand 5 (CCL5), prostaglandin E2 (PGE), and TNF-α. Selective ablation of IRE1a in leukocytes, or treatment with an IRE1a pharmacological inhibitor, mitigated kidney inflammation and prolonged the survival of mice with systemic C. albicans infection. Therefore, controlling IRE1α hyperactivation may be useful for impeding the immunopathogenic progression of disseminated candidiasis.This work was supported by NIH T32 5T32AI134632-02 and F31CA257631 training grants (to AE); the Cancer Research Institute–Irvington Institute Postdoctoral Fellowship Award (to CSC and CS); NIH/NCI Cancer Center Support Grant P30 CA008748 (to SFS); and NIH R01 NS114653 and R21 CA248106 (to EARS). This work was also supported by a Junta de Castilla y León/Fondo Social Europeo Fellowship (to JJF); the CSIC’s Global Health Platform (PTI Salud Global, to MSC); Plan Nacional de Salud y Farmacia Grant PID2020-113751RB-I00, funded by MCIN/AEI/ 10.13039/501100011033 (to MSC); Junta de Castilla y León/Fondo Social Europeo Grant VA175P20 (to MSC); NIH grant R01 DK121977 and the Burroughs Wellcome Fund Investigator in the Pathogenesis of Infectious Diseases Award (to IDI); NIH R37 093808, NIH R01 139632, NIH R21 142639, and the Burroughs Wellcome Fund Investigator in the Pathogenesis of Infectious Diseases (to TMH); NIH R01 NS114653, NIH R01 CA271619, NIH R21 CA248106, US Department of Defense OC150431, OC200166, and OC200224, the Mark Foundation for Cancer Research ASPIRE Award, and The Pershing Square Sohn Foundation (to JRCR)

Recognition and control of neutrophil extracellular trap formation by MICL

Acknowledgements We thank the staff of the animal facilities at the University of Aberdeen and the University of Exeter for support and care for animals; C. Paterson from the University of Glasgow for assistance in establishing a Material Transfer Agreement; C. Parkin and D. Thompson for support with microscopy; and M. Stacey for valuable input. We acknowledge funding from the Wellcome Trust (102705 and 097377), Versus Arthritis (21164, 20775 and 21156), the US National Institutes of Health (R01DK121977 and R01AI163007), Versus Arthritis Centre of Excellence, Medical Research Council (MR/L020211/1) and the MRC Centre for Medical Mycology (MR/N006364/1). SLE tissue samples were provided by the Imperial College Healthcare Tissue Bank funded by the National Institute for Health Research (NIHR), Biomedical Research Centre based at the Imperial College Healthcare NHS Trust and Imperial College London. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.Peer reviewe

Endocytosis of commensal antigens by intestinal epithelial cells regulates mucosal T cell homeostasis

Commensal bacteria influence host physiology, without invading host tissues. We show that proteins from segmented filamentous bacteria (SFB) are transferred into intestinal epithelial cells (IECs) through adhesion-directed endocytosis that is distinct from the clathrin-dependent endocytosis of invasive pathogens. This process transfers microbial cell wall–associated proteins, including an antigen that stimulates mucosal T helper 17 (T_H17) cell differentiation, into the cytosol of IECs in a cell division control protein 42 homolog (CDC42)–dependent manner. Removal of CDC42 activity in vivo led to disruption of endocytosis induced by SFB and decreased epithelial antigen acquisition, with consequent loss of mucosal T_H17 cells. Our findings demonstrate direct communication between a resident gut microbe and the host and show that under physiological conditions, IECs acquire antigens from commensal bacteria for generation of T cell responses to the resident microbiota

Immunological Consequences of Intestinal Fungal Dysbiosis

Compared to bacteria, the role of fungi within the intestinal microbiota is poorly understood. In this study we investigated whether the presence of a "healthy" fungal community in the gut is important for modulating immune function. Prolonged oral treatment of mice with antifungal drugs resulted in increased disease severity in acute and chronic models of colitis, and also exacerbated the development of allergic airway disease. Microbiota profiling revealed restructuring of fungal and bacterial communities. Specifically, representation of Candida spp. was reduced, while Aspergillus, Wallemia, and Epicoccum spp. were increased. Oral supplementation with a mixture of three fungi found to expand during antifungal treatment (Aspergillus amstelodami, Epicoccum nigrum, and Wallemia sebi) was sufficient to recapitulate the exacerbating effects of antifungal drugs on allergic airway disease. Taken together, these results indicate that disruption of commensal fungal populations can influence local and peripheral immune responses and enhance relevant disease states

Immune regulation by fungal strain diversity in inflammatory bowel disease

The fungal microbiota (mycobiota) is an integral part of the complex multi-kingdom microbial community colonizing the mammalian gastrointestinal tract and plays an important role in immune regulation(1–6). Although aberrant mycobiota changes have been linked to several diseases including inflammatory bowel disease (IBD)(3–9), it is currently unknown whether fungal species captured by deep sequencing represent living organisms and whether specific fungi have functional consequences for disease development in affected individuals. Here we developed a translational platform for the functional exploration of the mycobiome at a fungal strain- and patient-specific level. Combining high-resolution mycobiota-sequencing, fungal culturomics and genomics, CRISPR/Cas9-based fungal strain editing system, in vitro functional immunoreactivity assays and in vivo models, this platform allows to explore host-fungal crosstalk within the human gut. We discovered a rich genetic diversity of opportunistic Candida albicans strains that dominated the colonic mucosa of IBD patients. Among these human gut-derived isolates, strains with high immune cell-damaging capacity (HD strains) reflect disease features of individual ulcerative colitis patients and aggravated intestinal inflammation in vivo through IL-1β-dependent mechanisms. Niche-specific inflammatory immunity and Th17 antifungal responses by HD strains in the gut were dependent upon the C. albicans secreted peptide toxin candidalysin during the transition from a benign commensal to a pathobiont state. These findings unveil the strain-specific nature of host-fungal interactions in the human gut and highlight new diagnostic and therapeutic targets for diseases of inflammatory origin

Malassezia Is Associated with Crohn’s Disease and Exacerbates Colitis in Mouse Models

Inflammatory bowel disease (IBD) is characterized by alterations in the intestinal microbiota and altered immune responses to gut microbiota. Evidence is accumulating that IBD is influenced by not only commensal bacteria but also commensal fungi. We characterized fungi directly associated with the intestinal mucosa in healthy people and Crohn's disease patients and identified fungi specifically abundant in patients. One of these, the common skin resident fungus Malassezia restricta, is also linked to the presence of an IBD-associated polymorphism in the gene for CARD9, a signaling adaptor important for anti-fungal defense. M. restricta elicits innate inflammatory responses largely through CARD9 and is recognized by Crohn's disease patient anti-fungal antibodies. This yeast elicits strong inflammatory cytokine production from innate cells harboring the IBD-linked polymorphism in CARD9 and exacerbates colitis via CARD9 in mouse models of disease. Collectively, these results suggest that targeting specific commensal fungi may be a therapeutic strategy for IBD