Essential role for autophagy during invariant NKT cell development.

Autophagy is an evolutionarily conserved cellular homeostatic pathway essential for development, immunity, and cell death. Although autophagy modulates MHC antigen presentation, it remains unclear whether autophagy defects impact on CD1d lipid loading and presentation to invariant natural killer T (iNKT) cells and on iNKT cell differentiation in the thymus. Furthermore, it remains unclear whether iNKT and conventional T cells have similar autophagy requirements for differentiation, survival, and/or activation. We report that, in mice with a conditional deletion of the essential autophagy gene Atg7 in the T-cell compartment (CD4 Cre-Atg7(-/-)), thymic iNKT cell development--unlike conventional T-cell development--is blocked at an early stage and mature iNKT cells are absent in peripheral lymphoid organs. The defect is not due to altered loading of intracellular iNKT cell agonists; rather, it is T-cell-intrinsic, resulting in enhanced susceptibility of iNKT cells to apoptosis. We show that autophagy increases during iNKT cell thymic differentiation and that it developmentally regulates mitochondrial content through mitophagy in the thymus of mice and humans. Autophagy defects result in the intracellular accumulation of mitochondrial superoxide species and subsequent apoptotic cell death. Although autophagy-deficient conventional T cells develop normally, they show impaired peripheral survival, particularly memory CD8(+) T cells. Because iNKT cells, unlike conventional T cells, differentiate into memory cells while in the thymus, our results highlight a unique autophagy-dependent metabolic regulation of adaptive and innate T cells, which is required for transition to a quiescent state after population expansion.

Interferon-γ induces leucine-rich repeat kinase LRRK2 via extracellular signal-regulated kinase ERK5 in macrophages.

The gene encoding leucine-rich repeat kinase 2 (LRRK2) comprises a major risk factor for Parkinson's disease. Recently, it has emerged that LRRK2 plays important roles in the immune system. LRRK2 is induced by interferon-γ (IFN-γ) in monocytes, but the signaling pathway is not known. Here, we show that IFN-γ-mediated induction of LRRK2 was suppressed by pharmacological inhibition and RNA interference of the extracellular signal-regulated kinase 5 (ERK5). This was confirmed by LRRK2 immunostaining, which also revealed that the morphological responses to IFN-γ were suppressed by ERK5 inhibitor treatment. Both human acute monocytic leukemia THP-1 cells and human peripheral blood monocytes stimulated the ERK5-LRRK2 pathway after differentiation into macrophages. Thus, LRRK2 is induced via a novel, ERK5-dependent IFN-γ signal transduction pathway, pointing to new functions of ERK5 and LRRK2 in human macrophages. Leucine-rich repeat kinase 2 (LRRK2) is a major risk factor for the development of Parkinson's disease (PD). However, the role of LRRK2 in the affected neurons remains enigmatic. Recently, LRRK2 has been reported to be strongly expressed in the immune system. Here, we demonstrate that LRRK2 is induced by Interferon gamma via extracellular signal-regulated kinase 5 (ERK5) in macrophages, thus providing new insights in LRRK2 and ERK5 biology.

The effect of SGLT2 inhibitors on the endothelium and the microcirculation: from bench to bedside and beyond.

AIMS: The beneficial cardiovascular effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors irrespective of the presence of diabetes mellitus are nowadays well established and they already constitute a significant pillar for the management of heart failure, irrespective of the ejection fraction. The exact underlying mechanisms accountable for these effects, however, remain largely unknown. The direct effect on endothelial function and microcirculation is one of the most well studied. The broad range of studies presented in this review aims to link all available data from the bench to bedside and highlight the existing gaps as well as the future directions in the investigations concerning the effects of SGLT2 inhibitors on the endothelium and the microcirculation. METHODS AND RESULTS: An extensive search has been conducted using the MEDLINE/PubMed database in order to identify the relevant studies. Preclinical data suggest that SGLT2 inhibitors directly affect endothelial function independently of glucose and specifically via several interplaying molecular pathways, resulting in improved vasodilation, increased NO production, enhanced mitochondrial homeostasis, endothelial cell viability, and angiogenesis as well as attenuation of oxidative stress and inflammation. Clinical data systematically confirm this beneficial effect on the endothelium, whereas the evidence concerning the effect on the microcirculation is conflicting. CONCLUSION: Preclinical and clinical studies indicate that SGLT2 inhibitors attenuate endothelial and microvascular dysfunction via a combination of mechanisms, which play a role in their beneficial cardiovascular effect.

The Impact of the Patras Carnival on the Course of the COVID-19 Pandemic and the Outbreak of Influenza A: A Multicenter Cross-Sectional Study.

Background: We investigated the impact of the indoor mass gathering of young people during the Patras Carnival in Greece on the course of the COVID-19 pandemic and the influenza A epidemic. Materials and Methods: For influenza A, we tested 331 subjects with high fever (>38 °C), who arrived at five separate private laboratories over a two-week period after the carnival, via rapid test. One hundred and eighty-eight of them were young adults (17−35 years old), all unvaccinated against influenza A but all immunized against SARS-CoV-2, either through vaccination or previous infection. For the SARS-CoV-2 pandemic, we tested 2062 subjects at two time periods, two weeks before and two weeks after the carnival, also via rapid test. Additionally, we examined 42 samples positive for influenza A and 51 samples positive for SARS-CoV-2 for the possibility of co-infection via molecular testing (i.e., RT-PCR). Results: 177/331 (53.5%) subjects tested positive for influenza A, and 109/177 (61.6%) of the positive subjects were young adults, and 93/109 (85.3%) of these subjects were tested in the first week after the carnival. Additionally, 42 samples of those subjects were molecularly tested, and 5 were found negative for influenza A but positive for SARS-CoV-2. Regarding the SARS-CoV-2 pandemic, the increase in the positivity index for young adults between the pre-carnival and post-carnival periods was moderate. Conclusions: Our study indicates that the indoor mass gathering of young people during the carnival contributed to the outbreak of an influenza A epidemic and had a moderate but not statistically significant impact on the course of the SARS-CoV-2 pandemic, corroborating the crucial role of vaccination against the epidemic's waves. It also showed the need for the use of high-quality rapid tests for their management.

Acute hepatitis and liver injury in hospitalized patients with COVID­19 infection.

Coronavirus disease 2019 (COVID-19) is a systemic illness with an increased host inflammatory response that affects multiple extra-pulmonary organs, including the gastrointestinal tract. Abnormalities in liver biochemistry have been observed in a significant proportion of patients with COVID-19 upon admission, and this proportion increases with hospitalization. These abnormalities are typically manifested as elevations in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, with less frequently detected elevations in the levels of cholestatic enzymes. Elevated aminotransaminase levels have been linked to an increased risk of mortality and complications, indicating the severity of COVID-19 infection. The present study evaluated the prevalence and the baseline factors associated with the development of acute hepatitis (ΑΗ), liver injury (LI) and associated patterns, as well as the presence of abnormalities in the levels of aminotransferases at discharge in the same cohort. For this purpose, 1,304 patients with confirmed COVID-19 infection were enrolled in the study. According to the results obtained, AST levels at baseline were the only independent factor for AH during hospital stay, while AST, alkaline phosphatase and ferritin levels were independent baseline factors for the development of LI. The patients with hepatocellular, compared to those with cholestatic LI, exhibited similar survival rates, as well as similarities in the development of acute kidney injury and the need for oxygen via high-flow nasal cannula and/or mechanical ventilation. In addition, age and ALT were independent risk factors for persistent abnormal values of AST and ALT at discharge.

Prednisolone treatment induces tolerogenic dendritic cells and a regulatory milieu in myasthenia gravis patients.

FOXP3-expressing naturally occurring CD4(+)CD25(high) T regulatory cells (Treg) are relevant in the control of autoimmunity, and a defect in this cell population has been observed in several human autoimmune diseases. We hypothesized that altered functions of peripheral Treg cells might play a role in the immunopathogenesis of myasthenia gravis, a T cell-dependent autoimmune disease characterized by the presence of pathogenic autoantibodies specific for the nicotinic acetylcholine receptor. We report in this study a significant decrease in the in vitro suppressive function of peripheral Treg cells isolated from myasthenia patients in comparison to those from healthy donors. Interestingly, Treg cells from prednisolone-treated myasthenia gravis patients showed an improved suppressive function compared with untreated patients, suggesting that prednisolone may play a role in the control of the peripheral regulatory network. Indeed, prednisolone treatment prevents LPS-induced maturation of monocyte-derived dendritic cells by hampering the up-regulation of costimulatory molecules and by limiting secretion of IL-12 and IL-23, and enhancing IL-10. In addition, CD4(+) T cells cultured in the presence of such tolerogenic dendritic cells are hyporesponsive and can suppress autologous CD4(+) T cell proliferation. The results shown in this study indicate that prednisolone treatment promotes an environment that favors immune regulation rather than inflammation.

Processing of two latent membrane protein 1 MHC class I epitopes requires tripeptidyl peptidase II involvement.

The EBV Ag latent membrane protein 1 (LMP1) has been described as a potential target for T cell immunotherapy in EBV-related malignancies. However, only a few CD8(+) T cell epitopes are known, and the benefit of LMP1-specific T cell immunotherapy has not yet been proven. In this work, we studied the processing of the two LMP1 HLA-A02-restricted epitopes, YLLEMLRWL and YLQQNWWTL. We found that target cells endogenously expressing the native LMP1 are not recognized by CTLs specific for these epitopes because the N-terminal part of LMP1 limits the efficiency of epitope generation. We further observed that the proteasome is not required for the generation of both epitopes and that the YLLEMLRWL epitope seems to be destroyed by the proteasome, because blocking of proteasomal activities enhanced specific CTL activation. Activation of LMP1-specific CTLs could be significantly reduced after inhibition of the tripeptidyl peptidase II, suggesting a role for this peptidase in the processing of both epitopes. Taken together, our results demonstrate that the MHC class I-restricted LMP1 epitopes studied in this work are two of very few epitopes known to date to be processed proteasome independently by tripeptidyl peptidase II.

FOXN1 forms higher-order nuclear condensates displaced by mutations causing immunodeficiency.

The transcription factor FOXN1 is a master regulator of thymic epithelial cell (TEC) development and function. Here, we demonstrate that FOXN1 expression is differentially regulated during organogenesis and participates in multimolecular nuclear condensates essential for the factor's transcriptional activity. FOXN1's C-terminal sequence regulates the diffusion velocity within these aggregates and modulates the binding to proximal gene regulatory regions. These dynamics are altered in a patient with a mutant FOXN1 that is modified in its C-terminal sequence. This mutant is transcriptionally inactive and acts as a dominant negative factor displacing wild-type FOXN1 from condensates and causing athymia and severe lymphopenia in heterozygotes. Expression of the mutated mouse ortholog selectively impairs mouse TEC differentiation, revealing a gene dose dependency for individual TEC subtypes. We have therefore identified the cause for a primary immunodeficiency disease and determined the mechanism by which this FOXN1 gain-of-function mutant mediates its dominant negative effect.

Cathepsin G is differentially expressed in primary human antigen-presenting cells.

Cathepsins are required for the processing of antigens in order to make them suitable for loading on major histocompatibility complex (MHC) class II molecules, for subsequent presentation to CD4(+) T cells. It was shown that antigen processing in monocyte-derived dendritic cells (DC), a commonly used DC model, is different from that of primary human DC. Here, we report that the two subsets of human myeloid DC (mDC) and plasmacytoid DC (pDC) differ in their cathepsin distribution. The serine protease cathepsin G (CatG) was detected in mDC1, mDC2, pDC, cortical thymic epithelial cells (cTEC) and high levels of CatG were determined in pDC. To address the role of CatG in the processing and presentation of a Multiple Sclerosis-associated autoantigen myelin basic protein (MBP), we used a non-CatG expressing fibroblast cell line and fibroblasts, which were preloaded with purified CatG. We find that preloading fibroblasts with CatG results in a decrease of MBP84-98-specific T cell proliferation, when compared to control cells. Our data suggest a different processing signature in primary human antigen-presenting cells and CatG may be of functional importance.

HDAC inhibitors and their potential applications to glioblastoma therapy.

Natural killer (NK) cells are integral components of the antitumor immune response. The downregulation of ligands for NK-cell stimulatory receptors represents a strategy whereby glioblastoma cells can evade NK-cell attacks. Histone deacetylase inhibitors can stimulate the (re)expression of these ligands, driving cytotoxic responses against glioblastoma cells that efficiently inhibit tumor growth.

The histone deacetylase inhibitor trichostatin a promotes apoptosis and antitumor immunity in glioblastoma cells.

Histone deacetylase inhibitors (HDACi) have been described as multifunctional anticancer agents. The failure of conventional therapy for glioblastoma (GBM) renders this tumor an attractive target for immunotherapy. Innate immune cells, such as natural killer (NK) cells, play a crucial role in antitumor immune responses. Here, we describe how the HDACi trichostatin A (TSA) promotes apoptosis of tumor cells, as well as augments anti-GBM innate immune responses. In vitro treatment of GBM cells with TSA results in an up-regulation of the natural killer group-2 member-D (NKG2D) ligands major histocompatibility complex class I-related chain (MIC)-A and UL16 binding protein (ULBP)-2 at both mRNA and protein levels, rendering them susceptible to NK cell-mediated lysis. In vivo, TSA delays tumor growth of GBM xenografts. Both the in vitro and in vivo antitumor effect of TSA was significantly reduced by blocking NK cell activity. Our data suggest that HDACi, especially in combination with other clinical immunotherapeutical approaches, may be considered in a combined therapeutic approach for GBM.

Isolation of myeloid dendritic cells and epithelial cells from human thymus.

In this protocol we provide a method to isolate dendritic cells (DC) and epithelial cells (TEC) from the human thymus. DC and TEC are the major antigen presenting cell (APC) types found in a normal thymus and it is well established that they play distinct roles during thymic selection. These cells are localized in distinct microenvironments in the thymus and each APC type makes up only a minor population of cells. To further understand the biology of these cell types, characterization of these cell populations is highly desirable but due to their low frequency, isolation of any of these cell types requires an efficient and reproducible procedure. This protocol details a method to obtain cells suitable for characterization of diverse cellular properties. Thymic tissue is mechanically disrupted and after different steps of enzymatic digestion, the resulting cell suspension is enriched using a Percoll density centrifugation step. For isolation of myeloid DC (CD11c(+)), cells from the low-density fraction (LDF) are immunoselected by magnetic cell sorting. Enrichment of TEC populations (mTEC, cTEC) is achieved by depletion of hematopoietic (CD45(hi)) cells from the low-density Percoll cell fraction allowing their subsequent isolation via fluorescence activated cell sorting (FACS) using specific cell markers. The isolated cells can be used for different downstream applications.

Exploring the MHC-peptide matrix of central tolerance in the human thymus.

Ever since it was discovered that central tolerance to self is imposed on developing T cells in the thymus through their interaction with self-peptide major histocompatibility complexes on thymic antigen-presenting cells, immunologists have speculated about the nature of these peptides, particularly in humans. Here, to shed light on the so-far unknown human thymic peptide repertoire, we analyse peptides eluted from isolated thymic dendritic cells, dendritic cell-depleted antigen-presenting cells and whole thymus. Bioinformatic analysis of the 842 identified natural major histocompatibility complex I and II ligands reveals significant cross-talk between major histocompatibility complex-class I and II pathways and differences in source protein representation between individuals as well as different antigen-presenting cells. Furthermore, several autoimmune- and tumour-related peptides, from enolase and vimentin for example, are presented in the healthy thymus. 302 peptides are directly derived from negatively selecting dendritic cells, thus providing the first global view of the peptide matrix in the human thymus that imposes self-tolerance in vivo.

Human CD4+ T cells displaying viral epitopes elicit a functional virus-specific memory CD8+ T cell response.

The Ag-specific cellular recall response to herpes virus infections is characterized by a swift recruitment of virus-specific memory T cells. Rapid activation is achieved through formation of the immunological synapse and supramolecular clustering of signal molecules at the site of contact. During the formation of the immunological synapse, epitope-loaded MHC molecules are transferred via trogocytosis from APCs to T cells, enabling the latter to function as Ag-presenting T cells (T-APCs). The contribution of viral epitope expressing T-APCs in the regulation of the herpes virus-specific CD8+ T cell memory response remains unclear. Comparison of CD4+ T-APCs with professional APCs such as Ag-presenting CD40L-activated B cells (CD40B-APCs) demonstrated reduced levels of costimulatory ligands. Despite the observed differences, CD4+ T-APCs are as potent as CD40B-APCs in stimulating herpes virus-specific CD8+ T cells resulting in a greater than 35-fold expansion of CD8+ T cells specific for dominant and subdominant viral epitopes. Virus-specific CD8+ T cells generated by CD4+ T-APCs or CD40B-APCs showed both comparable effector function such as specific lysis of targets and cytokine production and also did not differ in their phenotype after expansion. These results indicate that viral epitope presentation by Ag-specific CD4+ T cells may contribute to the rapid recruitment of virus-specific memory CD8+ T cells during a viral recall response.