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Indoleamine 2,3 dioxygenase 1 (IDO1), a leader tryptophan-degrading enzyme, represents a recognized immune checkpoint molecule. In neoplasia, IDO1 is often highly expressed in dendritic cells infiltrating the tumor and/or in tumor cells themselves, particularly in human melanoma. In dendritic cells, IDO1 does not merely metabolize tryptophan into kynurenine but, after phosphorylation of critical tyrosine residues in the non-catalytic small domain, it triggers a signaling pathway prolonging its immunoregulatory effects by a feed-forward mechanism. We here investigated whether the non-enzymatic function of IDO1 could also play a role in tumor cells by using B16-F10 mouse melanoma cells transfected with either the wild-type Ido1 gene (Ido1WT) or a mutated variant lacking the catalytic, but not signaling activity (Ido1H350A). As compared to the Ido1WT-transfected counterpart (B16WT), B16-F10 cells expressing Ido1H350A (B16H350A) were characterized by an in vitro accelerated growth mediated by increased Ras and Erk activities. Faster growth and malignant progression of B16H350A cells, also detectable in vivo, were found to be accompanied by a reduction in tumor-infiltrating CD8+ T cells and an increase in Foxp3+ regulatory T cells. Our data, therefore, suggest that the IDO1 signaling function can also occur in tumor cells and that alternative therapeutic approach strategies should be undertaken to effectively tackle this important immune checkpoint molecule. [ABSTRACT FROM AUTHOR]

Demonstrates that tryptophan metabolites in the kynurenine pathway induces the selective apoptosis in vitro of murine thymocytes and of Th1 but not Th2 cells. Induction of apoptosis in thymocytes by 3-hydroxyantranylic acid; Lack of Fas involvement in apoptosis induced by kynurenines; Effects of caspase inhibitors on kynurenine-induced T cell apoptosis.

Background: Allergen-specific immunotherapy (AIT) is able to restore immune tolerance to allergens in allergic patients. However, some patients do not or only poorly respond to current treatment protocols. Therefore, there is a need for deeper mechanistic insights and further improvement of treatment strategies. The relevance of the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, has been investigated in several inflammatory diseases, including allergic asthma. However, its potential role in AIT still needs to be addressed., Methods: A murine model of AIT in ovalbumin-induced allergic airway inflammation was performed in AhR-deficient (AhR -/- ) and wild-type mice. Furthermore, AIT was combined with the application of the high-affinity AhR agonist 10-chloro-7H-benzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (10-Cl-BBQ) as an adjuvant to investigate the effects of AhR activation on therapeutic outcome., Results: Although AhR -/- mice suffer stronger allergic responses than wild-type mice, experimental AIT is comparably effective in both. Nevertheless, combining AIT with the administration of 10-Cl-BBQ improved therapeutic effects by an AhR-dependent mechanism, resulting in decreased cell counts in the bronchoalveolar fluid, decreased pulmonary Th2 and Th17 cell levels, and lower sIgE levels., Conclusion: This study demonstrates that the success of AIT is not dependent on the AhR. However, targeting the AhR during AIT can help to dampen inflammation and improve tolerogenic vaccination. Therefore, AhR ligands might represent promising candidates as immunomodulators to enhance the efficacy of AIT., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Heine, Alessandrini, Grosch, Graß, Heldner, Schnautz, Grosch, Buters, Slusarenko, Krappmann, Fallarino, Ohnmacht, Schmidt-Weber and Blank.)

Dendritic cells (DCs) are essential orchestrators of immune responses and represent potential targets for immunomodulation in autoimmune diseases. Human amniotic fluid secretome is abundant in immunoregulatory factors, with extracellular vesicles (EVs) being a significant component. However, the impact of these EVs on dendritic cells subsets remain unexplored. In this study, we investigated the interaction between highly purified dendritic cell subsets and EVs derived from amniotic fluid stem cell lines (HAFSC-EVs). Our results suggest that HAFSC-EVs are preferentially taken up by conventional dendritic cell type 2 (cDC2) through CD29 receptor-mediated internalization, resulting in a tolerogenic DC phenotype characterized by reduced expression and production of pro-inflammatory mediators. Furthermore, treatment of cDC2 cells with HAFSC-EVs in coculture systems resulted in a higher proportion of T cells expressing the regulatory T cell marker Foxp3 compared to vehicle-treated control cells. Moreover, transfer of HAFSC-EV-treated cDC2s into an EAE mouse model resulted in the suppression of autoimmune responses and clinical improvement. These results suggest that HAFSC-EVs may serve as a promising tool for reprogramming inflammatory cDC2s towards a tolerogenic phenotype and for controlling autoimmune responses in the central nervous system, representing a potential platform for the study of the effects of EVs in DC subsets., (© 2024 The Author(s). Journal of Extracellular Vesicles published by Wiley Periodicals LLC on behalf of International Society for Extracellular Vesicles.)

Multiple sclerosis is a debilitating autoimmune disease, characterized by chronic inflammation of the central nervous system. While the significance of the gut microbiome on multiple sclerosis pathogenesis is established, the underlining mechanisms are unknown. We found that serum levels of the microbial postbiotic tryptophan metabolite indole-3-carboxaldehyde (3-IAld) inversely correlated with disease duration in multiple sclerosis patients. Much like the host-derived tryptophan derivative L-Kynurenine, 3-IAld would bind and activate the Aryl hydrocarbon Receptor (AhR), which, in turn, controls endogenous tryptophan catabolic pathways. As a result, in peripheral lymph nodes, microbial 3-IAld, affected mast-cell tryptophan metabolism, forcing mast cells to produce serotonin via Tph1. We thus propose a protective role for AhR-mast-cell activation driven by the microbiome, whereby natural metabolites or postbiotics will have a physiological role in immune homeostasis and may act as therapeutic targets in autoimmune diseases., (© 2024. The Author(s).)

Canine seminal plasma is a complex fluid containing proteins, peptides, enzymes, hormones as well as extracellular vesicles that are involved in many physiological and pathological processes including reproduction. We examined the expression of the extracellular vesicles surface antigens Aminopeptidase-N (CD13) and Dipeptidyl peptidase IV (CD26) by flow cytometry. For this study, third fraction of the ejaculate, from fertile adult male German Shepherd dogs, was manually collected twice, two days apart. FACS analyses revealed that CD13 and CD26 are co-expressed on the 69.3 ± 3.7% of extracellular vesicles and only a 2.0 ± 0.5% of extracellular vesicles express CD26 alone. On the other hand, 28.6 ± 3.6% of seminal EVs express CD13 alone. Our results agree with the hypothesis that CD26 needs to be co-expressed with other signal-transducing molecules, while CD13, can perform functions independently of the presence or co-expression of CD26. The results obtained in normal fertile dogs could represent physiological expression of these enzymes. Therefore, it would be interesting to carry out further studies to evaluate the expression of CD13 and CD26 on extracellular vesicles as biomarker for prostate pathological condition in dogs., (© 2023. The Author(s).)

Src is a protein tyrosine kinase commonly activated downstream of transmembrane receptors and plays key roles in cell growth, migration, and survival signaling pathways. In conventional dendritic cells (cDCs), Src is involved in the activation of the non-enzymatic functions of indoleamine 2,3-dioxygenase 1 (IDO1), an immunoregulatory molecule endowed with both catalytic activity and signal transducing properties. Prompted by the discovery that the metabolite spermidine confers a tolerogenic phenotype on cDCs that is dependent on both the expression of IDO1 and the activity of Src kinase, we here investigated the spermidine mode of action. We found that spermidine directly binds Src in a previously unknown allosteric site located on the backside of the SH2 domain and thus acts as a positive allosteric modulator of the enzyme. Besides confirming that Src phosphorylates IDO1, here we showed that spermidine promotes the protein-protein interaction of Src with IDO1. Overall, this study may pave the way toward the design of allosteric modulators able to switch on/off the Src-mediated pathways, including those involving the immunoregulatory protein IDO1., Competing Interests: SR, MG, GS, EB, SA, EP, CV, CO, AM, FF, GM No competing interests declared, (© 2023, Rossini et al.)

Background: Chronic systemic inflammation reduces the bioavailability of circulating endothelial progenitor cells (EPCs). Indoleamine 2,3-dioxygenase 1 (IDO1), a key enzyme of immune tolerance catalyzing the initial step of tryptophan degradation along the so-called l-kynurenine (l-kyn) pathway, that is induced by inflammatory stimuli and exerts anti-inflammatory effects. A specific relationship between IDO1 activity and circulating EPC numbers has not yet been investigated., Methods: In this study, circulating EPCs were examined in mice treated with low doses of lipopolysaccharide (LPS) to mimic low-grade inflammation. Moreover, the association between IDO1 activity and circulating EPCs was studied in a cohort of 277 patients with variable systemic low-grade inflammation., Results: Repeated low doses of LPS caused a decrease in circulating EPCs and l-kyn supplementation, mimicking IDO1 activation, significantly increased EPC numbers under homeostatic conditions preventing EPC decline in low-grade endotoxemia. Accordingly, in patients with variable systemic low-grade inflammation, there was a significant interaction between IDO1 activity and high-sensitivity C-reactive protein (hs-CRP) in predicting circulating EPCs, with high hs-CRP associated with significantly lower EPCs at low IDO1 activity but not at high IDO1 activity., Interpretation: Overall, these findings demonstrate that systemic low-grade inflammation reduces circulating EPCs. However, high IDO1 activity and l-kyn supplementation limit circulating EPC loss in low-grade inflammation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Mannarino, Bianconi, Scalisi, Franceschini, Manni, Cucci, Bagaglia, Mencarelli, Giglioni, Ricciuti, Figorilli, Pieroni, Cosentini, Padiglioni, Colangelo, Fuchs, Puccetti, Follenzi, Pirro, Gargaro and Fallarino.)

In chronic lymphocytic leukaemia (CLL) the efficacy of SARS-CoV-2 vaccination remains unclear as most studies have focused on humoral responses. Here we comprehensively examined humoral and cellular responses to vaccine in CLL patients. Seroconversion was observed in 55.2% of CLL with lower rate and antibody titres in treated patients. T-cell responses were detected in a significant fraction of patients. CD4 + and CD8 + frequencies were significantly increased independent of serology with higher levels of CD4 + cells in patients under a Bruton tyrosine kinase (BTK) or a B-cell lymphoma 2 (BCL-2) inhibitor. Vaccination skewed CD8 + cells towards a highly cytotoxic phenotype, more pronounced in seroconverted patients. A high proportion of patients showed spike-specific CD4 + and CD8 + cells producing interferon gamma (IFNγ) and tumour necrosis factor alpha (TNFα). Patients under a BTK inhibitor showed increased production of IFNγ and TNFα by CD4 + cells. Vaccination induced a Th1 polarization reverting the Th2 CLL T-cell profile in the majority of patients with lower IL-4 production in untreated and BTK-inhibitor-treated patients. Such robust T-cell responses may have contributed to remarkable protection against hospitalization and death in a cohort of 540 patients. Combining T-cell metrics with seroprevalence may yield a more accurate measure of population immunity in CLL, providing consequential insights for public health., (© 2022 The Authors. British Journal of Haematology published by British Society for Haematology and John Wiley & Sons Ltd.)

Extracellular vesicles (EVs) are membrane-enclosed particles secreted by cells and circulating in body fluids. Initially considered as a tool to dispose of unnecessary material, they are now considered an additional method to transmit cell signals. Aging is characterized by a progressive impairment of the physiological functions of tissues and organs. The causes of aging are complex and interconnected, but there is consensus that genomic instability, telomere erosion, epigenetic alteration, and defective proteostasis are primary hallmarks of the aging process. Recent studies have provided evidence that many of these primary stresses are associated with an increased release of EVs in cell models, able to spread senescence signals in the recipient cell. Additional investigations on the role of EVs during aging also demonstrated the great potential of EVs for the modulation of age-related phenotypes and for pro-rejuvenation therapies, potentially beneficial for many diseases associated with aging. Here we reviewed the current literature on EV secretion in senescent cell models and in old vs. young individual body fluids, as well as recent studies addressing the potential of EVs from different sources as an anti-aging tool. Although this is a recent field, the robust consensus on the altered EV release in aging suggests that altered EV secretion could be considered an emerging hallmark of aging.

The environmental light/dark cycle has left its mark on the body's physiological functions to condition not only our inner biology, but also the interaction with external cues. In this scenario, the circadian regulation of the immune response has emerged as a critical factor in defining the host-pathogen interaction and the identification of the underlying circuitry represents a prerequisite for the development of circadian-based therapeutic strategies. The possibility to track down the circadian regulation of the immune response to a metabolic pathway would represent a unique opportunity in this direction. Herein, we show that the metabolism of the essential amino acid tryptophan, involved in the regulation of fundamental processes in mammals, is regulated in a circadian manner in both murine and human cells and in mouse tissues. By resorting to a murine model of pulmonary infection with the opportunistic fungus Aspergillus fumigatus , we showed that the circadian oscillation in the lung of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO)1, generating the immunoregulatory kynurenine, resulted in diurnal changes in the immune response and the outcome of fungal infection. In addition, the circadian regulation of IDO1 drives such diurnal changes in a pre-clinical model of cystic fibrosis (CF), an autosomal recessive disease characterized by progressive lung function decline and recurrent infections, thus acquiring considerable clinical relevance. Our results demonstrate that the circadian rhythm at the intersection between metabolism and immune response underlies the diurnal changes in host-fungal interaction, thus paving the way for a circadian-based antimicrobial therapy., (© The Author(s) 2023. Published by Oxford University Press on behalf of National Academy of Sciences.)

In pregnancy, human amniotic fluid extracellular vesicles (HAF-EVs) exert anti-inflammatory effects on T cells and on monocytes, supporting their immunoregulatory roles. The specific mechanisms are still not completely defined. The aim of this study was to investigate the ability of HAF-EVs, isolated from pregnant women who underwent amniocentesis and purified by gradient ultracentrifugation, to affect inflammasome activation in the human monocytes. Proteomic studies revealed that HAF-EV samples expressed several immunoregulatory molecules as well as small amounts of endotoxin. Surprisingly, metagenomic analysis shows the presence of specific bacterial strain variants associated with HAF-EVs as potential sources of the endotoxin. Remarkably, we showed that a single treatment of THP-1 cells with HAF-EVs triggered inflammasome activation, whereas the same treatment followed by LPS and ATP sensitization prevented inflammasome activation, a pathway resembling monocyte refractories. A bioinformatics analysis of microbiota-HAF-EVs functional pathways confirmed the presence of enzymes for endotoxin biosynthesis as well as others associated with immunoregulatory functions. Overall, these data suggest that HAF-EVs could serve as a source of the isolation of a specific microbiota during early pregnancy. Moreover, HAF-EVs could act as a novel system to balance immune training and tolerance by modulating the inflammasome in monocytes or other cells., Competing Interests: The authors declare that there is no conflict of interest.

Toll-like receptors (TLRs) are pivotal players in mediating immune responses. TLR4 is the main receptor for LPS, a strong activator of immune cells. LPS/TLR4-dependent pathway, by inducing NF-κB activation, is responsible for the release of several mediators, including IL-1β, one of the most powerful cytokines deeply involved in inflammatory and immune responses. The same pathway is also involved in NLRP3-inflammasome activation, essential for IL-1β maturation. NLRP3 is a major component of innate immune responses, being a crucial player of host immune defense against virus, bacterial, or fungal infections. NLRP3-inflammasome and IL-1β hyperactivation have been associated to the pathogenesis of a wide range of disorders and represent therapeutic targets for the development of new treatments of inflammasome-driven inflammatory and autoimmune diseases.Here, we describe an in vitro protocol to induce LPS/TLR4-dependent NLRP3-inflammasome/IL-1β activation in immune cells, in order to provide a useful assay to study the efficacy of different anti-inflammatory/immune-modulatory agents., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Objectives: Natural products are valuable sources of nutraceuticals for the prevention or treatment of ischemic stroke, a major cause of death and severe disability worldwide. Among the mechanisms implicated in cerebral ischemia-reperfusion damage, oxidative stress exerts a pivotal role in disease progression. Given the high antioxidant potential of most components of sunflower oil, we have explored its effects on ischemic brain injury produced in the mouse by transient occlusion of the middle cerebral artery (MCAo)., Key Findings: Intraperitoneal (i.p.) administration of sunflower oil at doses of 3 ml/kg (48 h, 24 h and 1 h before MCAo) significantly reduced brain infarct volume and oedema assessed 24 h after the insult. This neuroprotective treatment schedule also prevented the elevation of brain lipid peroxidation produced by MCAo-reperfusion injury. By contrast, doses of 0.03 ml/kg of sunflower oil resulted ineffective on both cerebral damage and lipid peroxidation. Although sunflower oil did not affect serum levels of Diacron-reactive oxygen metabolites (d-ROMs), both 0.03 and 3 ml/kg dosing regimens resulted in the preservation of serum biological antioxidant potential (BAP) that was otherwise dramatically reduced 24 h after MCAo., Conclusions: Sunflower oil represents a promising source of neuroprotective extracts/compounds that can be exploited for the prevention and/or treatment of cerebral ischemia., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Royal Pharmaceutical Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

BACKGROUND: Mucopolysaccharidosis type VI (MPS VI) is an inherited multisystem lysosomal disorder due to arylsulfatase B (ARSB) deficiency that leads to widespread accumulation of glycosaminoglycans (GAG), which are excreted in increased amounts in urine. MPS VI is characterized by progressive dysostosis multiplex, connective tissue and cardiac involvement, and hepatosplenomegaly. Enzyme replacement therapy (ERT) is available but requires life-long and costly intravenous infusions; moreover, it has limited efficacy on diseased skeleton and cardiac valves, compromised pulmonary function, and corneal opacities. METHODS: We enrolled nine patients with MPS VI 4 years of age or older in a phase 1/2 open-label gene therapy study. After ERT was interrupted, patients each received a single intravenous infusion of an adeno-associated viral vector serotype 8 expressing ARSB. Participants were sequentially enrolled in one of three dose cohorts: low (three patients), intermediate (two patients), or high (four patients). The primary outcome was safety; biochemical and clinical end points were secondary outcomes. RESULTS: The infusions occurred without severe adverse events attributable to the vector, meeting the prespecified end point. Participants in the low and intermediate dose cohorts displayed stable serum ARSB of approximately 20% of the mean healthy value but returned to ERT by 14 months after gene therapy because of increased urinary GAG. Participants in the high-dose cohort had sustained serum ARSB of 30% to 100% of the mean healthy value and a modest urinary GAG increase that did not reach a concentration at which ERT reintroduction was needed. In the high-dose group, there was no clinical deterioration for up to 2 years after gene therapy. CONCLUSIONS: Liver-directed gene therapy for participants with MPS VI did not have a dose-limiting side-effect and adverse event profile; high-dose treatment resulted in ARSB expression over at least 24 months with preliminary evidence of disease stabilization. (Funded by the Telethon Foundation ETS, the European Commission Seventh Framework Programme, and the Isaac Foundation; ClinicalTrials.gov number, NCT03173521; EudraCT number, 2016-002328-10.)

Conventional dendritic cells (cDCs), cDC1 and cDC2, act both to initiate immunity and maintain self-tolerance. The tryptophan metabolic enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is used by cDCs in maintaining tolerance, but its role in different subsets remains unclear. At homeostasis, only mature CCR7 + cDC1 expressed IDO1 that was dependent on IRF8. Lipopolysaccharide treatment induced maturation and IDO1-dependent tolerogenic activity in isolated immature cDC1, but not isolated cDC2. However, both human and mouse cDC2 could induce IDO1 and acquire tolerogenic function when co-cultured with mature cDC1 through the action of cDC1-derived l-kynurenine. Accordingly, cDC1-specific inactivation of IDO1 in vivo exacerbated disease in experimental autoimmune encephalomyelitis. This study identifies a previously unrecognized metabolic communication in which IDO1-expressing cDC1 cells extend their immunoregulatory capacity to the cDC2 subset through their production of tryptophan metabolite l-kynurenine. This metabolic axis represents a potential therapeutic target in treating autoimmune demyelinating diseases., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Liver gene therapy with adeno-associated viral (AAV) vectors is under clinical investigation for haemophilia A (HemA), the most common inherited X-linked bleeding disorder. Major limitations are the large size of the F8 transgene, which makes packaging in a single AAV vector a challenge, as well as the development of circulating anti-F8 antibodies which neutralise F8 activity. Taking advantage of split-intein-mediated protein trans-splicing, we divided the coding sequence of the large and highly secreted F8-N6 variant in two separate AAV-intein vectors whose co-administration to HemA mice results in the expression of therapeutic levels of F8 over time. This occurred without eliciting circulating anti-F8 antibodies unlike animals treated with the single oversized AAV-F8 vector under clinical development. Therefore, liver gene therapy with AAV-F8-N6 intein should be considered as a potential therapeutic strategy for HemA., (© 2022 The Authors. Published under the terms of the CC BY 4.0 license.)

An immunoregulatory role of stem cells, often mediated by their secretome, has been claimed by several studies. Stem cell-derived extracellular vesicles (EVs) are crucial components of the secretome. EVs, a heterogeneous group of membranous vesicles released by many cell types into the extracellular space, are now considered as an additional mechanism for intercellular communication. In this study, we aimed at investigating whether human amniotic stem cell-derived extracellular vesicles (HASC-EVs) were able to interfere with inflammasome activation in the THP-1 cell line. Two subsets of HASC-EVs were collected by sequential centrifugation, namely HASC-P10 and HASC-P100. We demonstrated that HASC-EVs were neither internalized into nor undertake a direct interaction with THP-1 cells. We showed that HASC-P10 and P100 were able to intrinsically produce ATP, which was further converted to adenosine by 5'-nucleotidase (CD73) and ectonucleoside triphosphate diphosphohydrolase-1 (CD39). We found that THP-1 cells conditioned with both types of HASC-EVs failed to activate the NLRP3/caspase-1/inflammasome platform in response to LPS and ATP treatment by a mechanism involving A2a adenosine receptor activation. These results support a role for HASC-EVs as independent metabolic units capable of modifying the cellular functions, leading to anti-inflammatory effects in monocytic cells., (© 2022 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Autophagy selectively degrades aggregation-prone misfolded proteins caused by defective cellular proteostasis. However, the complexity of autophagy may prevent the full appreciation of how its modulation could be used as a therapeutic strategy in disease management. Here, we define a molecular pathway through which recombinant IL-1 receptor antagonist (IL-1Ra, anakinra) affects cellular proteostasis independently from the IL-1 receptor (IL-1R1). Anakinra promoted H2O2-driven autophagy through a xenobiotic sensing pathway involving the aryl hydrocarbon receptor that, activated through the indoleamine 2,3-dioxygenase 1-kynurenine pathway, transcriptionally activated NADPH oxidase 4 independent of the IL-1R1. By coupling the mitochondrial redox balance to autophagy, anakinra improved the dysregulated proteostasis network in murine and human cystic fibrosis. We anticipate that anakinra may represent a therapeutic option in addition to its IL-1R1-dependent antiinflammatory properties by acting at the intersection of mitochondrial oxidative stress and autophagy with the capacity to restore conditions in which defective proteostasis leads to human disease.

Competing Interests: Declaration of interests None.

Objectives: Although hypovitaminosis D appears to be highly prevalent in patients with coronavirus disease 2019 (COVID-19), its impact on their prognosis remains unclear., Methods: In this study, serum 25-hydroxyvitamin D (Vit-D) level was measured in 200 patients hospitalized with COVID-19. The association between Vit-D and the composite endpoint of intensive care unit (ICU) admission/in-hospital death was explored using univariable and multivariable analyses. Also, serum Vit-D level in patients with COVID-19 was compared with that in age- and sex-balanced COVID-19-negative controls (i.e., 50 inpatients with sepsis)., Results: Serum Vit-D level was comparable between patients with COVID-19 and COVID-19-negative inpatients with sepsis (P = 0.397). No significant differences were found in serum Vit-D level according to COVID-19 severity at the time of hospital admission (P = 0.299). Incidence rates of the composite endpoint of ICU admission/in-hospital death did not differ significantly between patients with either Vit-D deficiency (i.e., Vit-D <20 ng/mL) or severe Vit-D deficiency (i.e., Vit-D <12 ng/mL) and those without (31% vs 35% with P = 0.649, and 34% vs 30% with P = 0.593, respectively). Vit-D level and status (i.e., Vit-D deficiency and severe Vit-D deficiency) were not prospectively associated with the risk of the composite endpoint of ICU admission/in-hospital death (P > 0.05 for all Cox regression models)., Conclusions: Regardless of the potential usefulness of Vit-D measurement to guide appropriate supplementation, Vit-D does not appear to provide helpful information for the stratification of in-hospital prognosis in patients with COVID-19., Competing Interests: Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Tryptophan catabolism is a major metabolic pathway utilized by several professional and non-professional antigen presenting cells to maintain immunological tolerance. Here we report that 3-hydroxy-L-kynurenamine (3-HKA) is a biogenic amine produced via an alternative pathway of tryptophan metabolism. In vitro, 3-HKA has an anti-inflammatory profile by inhibiting the IFN-γ mediated STAT1/NF-κΒ pathway in both mouse and human dendritic cells (DCs) with a consequent decrease in the release of pro-inflammatory chemokines and cytokines, most notably TNF, IL-6, and IL12p70. 3-HKA has protective effects in an experimental mouse model of psoriasis by decreasing skin thickness, erythema, scaling and fissuring, reducing TNF, IL-1β, IFN-γ, and IL-17 production, and inhibiting generation of effector CD8 + T cells. Similarly, in a mouse model of nephrotoxic nephritis, besides reducing inflammatory cytokines, 3-HKA improves proteinuria and serum urea nitrogen, overall ameliorating immune-mediated glomerulonephritis and renal dysfunction. Overall, we propose that this biogenic amine is a crucial component of tryptophan-mediated immune tolerance., (© 2021. The Author(s).)

The Aryl hydrocarbon receptor (AhR) is a critical regulator of both innate and adaptive immune responses, with potent immunomodulatory effects that makes this receptor an attractive molecular target for novel therapeutics. Accumulating evidence indicates that diverse-both host's and microbial-tryptophan metabolites profoundly regulate the immune system in the host via AhR, promoting either tolerance or immunity, largely as a function of the qualitative and quantitative nature of the metabolites being contributed by either source. Additional findings indicate that host and microbiota-derived tryptophan metabolic pathways can influence the outcome of immune responses to tumors. Here, we review recent studies on the role and modalities of AhR activation by various ligands, derived from either host-cell or microbial-cell tryptophan metabolic pathways, in the regulation of immune responses. Moreover, we highlight potential implications of those ligands and pathways in tumor immunotherapy, with particular relevance to checkpoint-blockade immune intervention strategies.

Mutations in the WFS1 gene, encoding wolframin (WFS1), cause endoplasmic reticulum (ER) stress and are associated with a rare autosomal-recessive disorder known as Wolfram syndrome (WS). WS is clinically characterized by childhood-onset diabetes mellitus, optic atrophy, deafness, diabetes insipidus and neurological signs. We identified two novel WFS1 mutations in a patient with WS, namely, c.316-1G > A (in intron 3) and c.757A > T (in exon 7). Both mutations, located in the N-terminal region of the protein, were predicted to generate a truncated and inactive form of WFS1. We found that although the WFS1 protein was not expressed in peripheral blood mononuclear cells (PBMCs) of the proband, no constitutive ER stress activation could be detected in those cells. In contrast, WS proband's PBMCs produced very high levels of proinflammatory cytokines (i.e. TNF-α, IL-1β, and IL-6) in the absence of any stimulus. WFS1 silencing in PBMCs from control subjects by means of small RNA interference also induced a pronounced proinflammatory cytokine profile. The same cytokines were also significantly higher in sera from the WS patient as compared to matched healthy controls. Moreover, the chronic inflammatory state was associated with a dominance of proinflammatory T helper 17 (Th17)-type cells over regulatory T (Treg) lymphocytes in the WS PBMCs. The identification of a state of systemic chronic inflammation associated with WFS1 deficiency may pave the way to innovative and personalized therapeutic interventions in WS., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Interleukin-4-induced-1 (IL4i1) is an amino acid oxidase secreted from immune cells. Recent observations have suggested that IL4i1 is pro-tumorigenic via unknown mechanisms. As IL4i1 has homologs in snake venoms (L-amino acid oxidases [LAAO]), we used comparative approaches to gain insight into the mechanistic basis of how conserved amino acid oxidases regulate cell fate and function. Using mammalian expressed recombinant proteins, we found that venom LAAO kills cells via hydrogen peroxide generation. By contrast, mammalian IL4i1 is non-cytotoxic and instead elicits a cell protective gene expression program inhibiting ferroptotic redox death by generating indole-3-pyruvate (I3P) from tryptophan. I3P suppresses ferroptosis by direct free radical scavenging and through the activation of an anti-oxidative gene expression program. Thus, the pro-tumor effects of IL4i1 are likely mediated by local anti-ferroptotic pathways via aromatic amino acid metabolism, arguing that an IL4i1 inhibitor may modulate tumor cell death pathways., Competing Interests: LZ, AF, CM, MR, GZ, SS, MG, SS, SS, CO, FF, AL, PM No competing interests declared, TK Thomas Köcher is affiliated with Vienna BioCenter Core Facilities GmbH. The author has no financial interests to declare., (© 2021, Zeitler et al.)

Indoleamine 2,3-dioxygenases (IDOs) degrade l-tryptophan to kynurenines and drive the de novo synthesis of nicotinamide adenine dinucleotide. Unsurprisingly, various invertebrates, vertebrates, and even fungi produce IDO. In mammals, IDO1 also serves as a homeostatic regulator, modulating immune response to infection via local tryptophan deprivation, active catabolite production, and non-enzymatic cell signaling. Whether fungal Idos have pleiotropic functions that impact on host-fungal physiology is unclear. Here, we show that Aspergillus fumigatus possesses three ido genes that are expressed under conditions of hypoxia or tryptophan abundance. Loss of these genes results in increased fungal pathogenicity and inflammation in a mouse model of aspergillosis, driven by an alternative tryptophan degradation pathway to indole derivatives and the host aryl hydrocarbon receptor. Fungal tryptophan metabolic pathways thus cooperate with the host xenobiotic response to shape host-microbe interactions in local tissue microenvironments., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

The aryl-hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates numerous cellular responses. Originally investigated in toxicology because of its ability to bind environmental contaminants, AhR has attracted enormous attention in the field of immunology in the last 20 years. In addition, the discovery of endogenous and plant-derived ligands points to AhR also having a crucial role in normal cell physiology. Thus, AhR is emerging as a promiscuous receptor that can mediate either toxic or physiologic effects upon sensing multiple exogenous and endogenous molecules. Within this scenario, several factors appear to contribute to the outcome of gene transcriptional regulation by AhR, including the nature of the ligand as such and its further metabolism by AhR-induced enzymes, the local tissue microenvironment, and the presence of coregulators or specific transcription factors in the cell. Here, we review the current knowledge on the array of transcription factors and coregulators that, by interacting with AhR, tune its transcriptional activity in response to endogenous and exogenous ligands.

Knowledge of a protein's spatial dynamics at the subcellular level is key to understanding its function(s), interactions, and associated intracellular events. Indoleamine 2,3-dioxygenase 1 (IDO1) is a cytosolic enzyme that controls immune responses via tryptophan metabolism, mainly through its enzymic activity. When phosphorylated, however, IDO1 acts as a signaling molecule in plasmacytoid dendritic cells (pDCs), thus activating genomic effects, ultimately leading to long-lasting immunosuppression. Whether the two activities-namely, the catalytic and signaling functions-are spatially segregated has been unclear. We found that, under conditions favoring signaling rather than catabolic events, IDO1 shifts from the cytosol to early endosomes. The event requires interaction with class IA phosphoinositide 3-kinases (PI3Ks), which become activated, resulting in full expression of the immunoregulatory phenotype in vivo in pDCs as resulting from IDO1-dependent signaling events. Thus, IDO1's spatial dynamics meet the needs for short-acting as well as durable mechanisms of immune suppression, both under acute and chronic inflammatory conditions. These data expand the theoretical basis for an IDO1-centered therapy in inflammation and autoimmunity., (© 2020 The Authors.)

HOPS/Tmub1 is a ubiquitously expressed transmembrane ubiquitin-like protein that shuttles between nucleus and cytoplasm during cell cycle progression. HOPS causes cell cycle arrest in G 0 /G 1 phase, an event associated to stabilization of p19 Arf , an important tumor suppressor protein. Moreover, HOPS plays an important role in driving centrosomal assembly and maintenance, mitotic spindle proper organization, and ultimately a correct cell division. Recently, HOPS has been described as an important regulator of p53, which acts as modifier, stabilizing p53 half-life and playing a key role in p53 mediating apoptosis after DNA damage. NF-κB is a transcription factor with a central role in many cellular events, including inflammation and apoptosis. Our experiments demonstrate that the transcriptional activity of the p65/RelA NF-κB subunit is regulated by HOPS. Importantly, Hops -/- cells have remarkable alterations of pro-inflammatory responses. Specifically, we found that HOPS enhances NF-κB activation leading to increase transcription of inflammatory mediators, through the reduction of IκBα stability. Notably, this effect is mediated by a direct HOPS binding to the E3 ubiquitin ligase TRAF6, which lessens TRAF6 stability ultimately leading increased IKK complex activation. These findings uncover a previously unidentified function of HOPS/Tmub1 as a novel modulator of TRAF6, regulating inflammatory responses driven by activation of the NF-κB signaling pathway. The comprehension on how HOPS/Tmub1 takes part to the inflammatory processes in vivo and whether this function is important in the control of proliferation and tumorigenesis could establish the basis for the development of novel pharmacological strategies.

Severe Acute Respiratory Syndrome-Coronavirus-2 is responsible for the current pandemic that has led to more than 10 million confirmed cases of Coronavirus Disease-19 (COVID-19) and over 500,000 deaths worldwide (4 July 2020). Virus-mediated injury to multiple organs, mainly the respiratory tract, activation of immune response with the release of pro-inflammatory cytokines, and overactivation of the coagulation cascade and platelet aggregation leading to micro- and macrovascular thrombosis are the main pathological features of COVID-19. Empirical multidrug therapeutic approaches to treat COVID-19 are currently used with extremely uncertain outcomes, and many others are being tested in clinical trials. Acetylsalicylic acid (ASA) has both anti-inflammatory and antithrombotic effects. In addition, a significant ASA-mediated antiviral activity against DNA and RNA viruses, including different human coronaviruses, has been documented. The use of ASA in patients with different types of infections has been associated with reduced thrombo-inflammation and lower rates of clinical complications and in-hospital mortality. However, safety issues related both to the risk of bleeding and to that of developing rare but serious liver and brain damage mostly among children (i.e., Reye's syndrome) should be considered. Hence, whether ASA might be a safe and reasonable therapeutic candidate to be tested in clinical trials involving adults with COVID-19 deserves further attention. In this review we provide a critical appraisal of current evidence on the anti-inflammatory, antithrombotic, and antiviral effects of ASA, from both a pre-clinical and a clinical perspective. In addition, the potential benefits and risks of use of ASA have been put in the context of the adult-restricted COVID-19 population.

Garcinoic acid (GA or δ-T3-13'COOH), is a natural vitamin E metabolite that has preliminarily been identified as a modulator of nuclear receptors involved in β-amyloid (Aβ) metabolism and progression of Alzheimer's disease (AD). In this study, we investigated GA's effects on Aβ oligomer formation and deposition. Specifically, we compared them with those of other vitamin E analogs and the soy isoflavone genistein, a natural agonist of peroxisome proliferator-activated receptor γ (PPARγ) that has therapeutic potential for managing AD. GA significantly reduced Aβ aggregation and accumulation in mouse cortical astrocytes. Similarly to genistein, GA up-regulated PPARγ expression and apolipoprotein E (ApoE) efflux in these cells with an efficacy that was comparable with that of its metabolic precursor δ-tocotrienol and higher than those of α-tocopherol metabolites. Unlike for genistein and the other vitamin E compounds, the GA-induced restoration of ApoE efflux was not affected by pharmacological inhibition of PPARγ activity, and specific activation of pregnane X receptor (PXR) was observed together with ApoE and multidrug resistance protein 1 (MDR1) membrane transporter up-regulation in both the mouse astrocytes and brain tissue. These effects of GA were associated with reduced Aβ deposition in the brain of TgCRND8 mice, a transgenic AD model. In conclusion, GA holds potential for preventing Aβ oligomerization and deposition in the brain. The mechanistic aspects of GA's properties appear to be distinct from those of other vitamin E metabolites and of genistein., Competing Interests: Conflict of interest—The authors declare that they have no conflicts of interest., (© 2020 Marinelli et al.)

The cellular prion protein (PrPC), a cell surface glycoprotein originally identified for its central role in prion diseases (also called transmissible spongiform encephalopathies), has recently been implicated in the pathogenesis of other neurodegenerative disorders, such as Alzheimer&rsquo;s and Parkinson&rsquo;s diseases, by acting as a toxicity-transducing receptor for different misfolded protein isoforms, or in some case by exerting neuroprotective effects. Interestingly, PrPC has also been reported to play unexpected functions outside the nervous system, for example by contributing to myelin homeostasis, regulating specific processes of the immune system and participating in various aspects of cancer progression. Collectively, these observations point to a much broader role for PrPC in physiological and disease processes than originally assumed. In this manuscript, we provide an overview of what is known about the role of PrPC beyond prion disorders and discuss the potential implications of targeting this protein in different diseases.