The role of dysbiosis in food allergy (FA) remains unclear. We found that dysbiotic fecal microbiota in FA infants evolved compositionally over time and failed to protect against FA in mice. Infants and mice with FA had decreased IgA and increased IgE binding to fecal bacteria, indicative of a broader breakdown of oral tolerance than hitherto appreciated. Therapy with Clostridiales species impacted by dysbiosis, either as a consortium or as monotherapy with Subdoligranulum variabile , suppressed FA in mice, as did a separate immunomodulatory Bacteroidales consortium. Bacteriotherapy induced regulatory T (Treg) cells expressing the transcription factor ROR-γt in a MyD88-dependent manner, which were deficient in FA infants and mice and ineffectively induced by their microbiota. Deletion of Myd88 or Rorc in Treg cells abrogated protection by bacteriotherapy. Thus, commensals activate a MyD88/ROR-γt pathway in nascent Treg cells to protect against FA, while dysbiosis impairs this regulatory response to promote disease.

Elucidating the mechanisms that sustain asthmatic inflammation is critical for precision therapies. We found that IL-6 and STAT3 transcription factor-dependent upregulation of Notch4 receptor on Iung tissue regulatory T (T reg ) cells is necessary for allergens and particulate matter pollutants to promote airway inflammation. Notch4 subverted T reg cells into T H 2 and T H 17 effector T (T eff ) cells by Wnt and Hippo pathway-dependent mechanisms. Wnt activation induced growth and differentiation factor 15 (GDF15) expression in T reg cells, which activated group 2 innate lymphoid cells (ILC2) to provide a feed-forward mechanism for aggravated inflammation. Notch4, Wnt and Hippo were upregulated on circulating T reg cells of asthmatics as a function of disease severity, in association with reduced T reg cell-mediated suppression. Our studies thus identify Notch4-mediated immune tolerance subversion as a fundamental mechanism that licenses tissue inflammation in asthma.

Summary Regulatory T cells (T reg cells) deficient in the transcription factor Foxp3 lack suppressor function and manifest a T effector (T eff ) cell-like phenotype. We demonstrate that Foxp3 deficiency dysregulates metabolic checkpoint kinase mTORC2 signaling and gives rise to augmented aerobic glycolysis and oxidative phosphorylation. Specific deletion of the mTORC2 adaptor gene Rictor in Foxp3-deficient T reg cells ameliorated disease in a Foxo1 transcription factor-dependent manner. Rictor deficiency reestablished a subset of T reg cell genetic circuits and suppressed the T eff cell-like glycolytic and respiratory programs, which contributed to immune dysregulation. Treatment of T reg cells from patients with FOXP3 deficiency with mTOR inhibitors similarly antagonized their T eff cell-like program and restored suppressive function. Thus, regulatory function can be reestablished in Foxp3-deficient T reg cells by targeting their metabolic pathways, providing opportunities to restore tolerance in T reg cell disorders.

Resistance of Aspergillus fumigatus conidia to desiccation and their capacity to reach the alveoli are partly due to the presence of a hydrophobic layer composed of a protein from the hydrophobin family, called RodA, which covers the conidial surface. In A. fumigatus there are seven hydrophobins (RodA–RodG) belonging to class I and III. Most of them have never been studied. We constructed single and multiple hydrophobin-deletion mutants until the generation of a hydrophobin-free mutant. The phenotype, immunogenicity, and virulence of the mutants were studied. RODA is the most expressed hydrophobin in sporulating cultures, whereas RODB is upregulated in biofilm conditions and in vivo Only RodA, however, is responsible for rodlet formation, sporulation, conidial hydrophobicity, resistance to physical insult or anionic dyes, and immunological inertia of the conidia. None of the hydrophobin plays a role in biofilm formation or its hydrophobicity. RodA is the only needed hydrophobin in A. fumigatus, conditioning the structure, permeability, hydrophobicity, and immune-inertia of the cell wall surface in conidia. Moreover, the defect of rodlets on the conidial cell wall surface impacts on the drug sensitivity of the fungus.

, inflammation-mediated severe lung damage and defective haemostasis are the main underlying reasons for morbidity and mortality in coronavirus disease 2019 (COVID-19) patients [1]. Several immunotherapies that target various inflammatory processes have been successfully used in COVID-19 patients and many other strategies are under evaluation [2, 3]. However, in view of dysregulated immune responses in severe COVID-19 patients, we suggest that CD4 + CD25 + FoxP3 + regulatory T-cell (Treg)-based strategies could be considered for patient management. Vigorous antimicrobial responses triggered against the pathogen can be detrimental to the host due to collateral tissue damage. Therefore, regulatory mechanisms, and in particular Tregs, are in place to ensure that inflammation is kept in check. Tregs are either thymus-derived or induced in the periphery and are classically known for stimulating immune tolerance, and preventing autoimmune and inflammatory diseases [4]. Tregs inhibit the activation of both innate and adaptive immune cells via inhibitory surface molecules (like cytotoxic T-lymphocyte antigen-4 (CTLA-4) and lymphocyte-activation gene-3) and secretion of immunosuppressive cytokines (interleukin (IL)-10, transforming growth factor-β and IL-35). Both Treg subsets are equally important to prevent inflammation-induced tissue damage during acute infections and to promote tissue repair, which is particularly shown in the influenza infection model [4, 5].

PD-L1 dictates the balance between Treg and IFN-γ responses induced by α-(1,3)-glucan. Our data provide a rationale for the exploitation of immunotherapeutic approaches that target PD-1-PD-L1 to enhance protective immune responses to A. fumigatus infections.

A cardinal feature of COVID-19 is lung inflammation and respiratory failure. In a prospective multi-country cohort of COVID-19 patients, we found that increased Notch4 expression on circulating regulatory T (Treg) cells was associated with disease severity, predicted mortality, and declined upon recovery. Deletion of Notch4 in Treg cells or therapy with anti-Notch4 antibodies in conventional and humanized mice normalized the dysregulated innate immunity and rescued disease morbidity and mortality induced by a synthetic analog of viral RNA or by influenza H1N1 virus. Mechanistically, Notch4 suppressed the induction by interleukin-18 of amphiregulin, a cytokine necessary for tissue repair. Protection by Notch4 inhibition was recapitulated by therapy with Amphiregulin and, reciprocally, abrogated by its antagonism. Amphiregulin declined in COVID-19 subjects as a function of disease severity and Notch4 expression. Thus, Notch4 expression on Treg cells dynamically restrains amphiregulin-dependent tissue repair to promote severe lung inflammation, with therapeutic implications for COVID-19 and related infections.

Basophils are a rare granulocyte population that has been associated with allergic and inflammatory responses. It is essential to understand the regulatory mechanisms by which basophils are kept in check, considering the impact of dysregulated basophil function on immune responses under different pathological conditions. Among immunoregulatory cells, CD4CD25FoxP3 regulatory T cells (T) are the key players that maintain immune tolerance. The mechanisms by which T regulate and suppress diverse immune cell subsets have been studied extensively, but the impact of T on basophil functions is not well understood. We report that human basophils are refractory to T-mediated suppression and found that T stimulate resting basophils to induce the expression of activation markers including CD69, CD203c, and CD13 and the release of basophil cytokines including IL-13, IL-8, and IL-4. Mechanistically, T could induce human basophil activation via IL-3 and STAT5 activation, whereas cellular contact was dispensable. Inhibition of either IL-3-IL-3 receptor interactions or STAT5 phosphorylation abrogated T-mediated activation of basophils. These results provide evidence of direct positive effects that human T have on basophil activation and reveal a previously unrecognized feature of this cell subset well known for immunosuppressive functions.