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Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone which is essential in eukaryotes. It is required for the activation and stabilization of a wide variety of client proteins and many of them are involved in important cellular pathways. Since Hsp90 affects numerous physiological processes such as signal transduction, intracellular transport, and protein degradation, it became an interesting target for cancer therapy. Structurally, Hsp90 is a flexible dimeric protein composed of three different domains which adopt structurally distinct conformations. ATP binding triggers directionality in these conformational changes and leads to a more compact state. To achieve its function, Hsp90 works together with a large group of cofactors, termed co-chaperones. Co-chaperones form defined binary or ternary complexes with Hsp90, which facilitate the maturation of client proteins. In addition, posttranslational modifications of Hsp90, such as phosphorylation and acetylation, provide another level of regulation. They influence the conformational cycle, co-chaperone interaction, and inter-domain communications. In this review, we discuss the recent progress made in understanding the Hsp90 machinery.

Hemophagocytic lymphohistocytosis (HLH) is characterized by fulminant cytokine storm leading to multiple organ dysfunction and high mortality. HLH is classified into familial (fHLH) and into secondary (sHLH). fHLH is rare and it is due to mutations of genes encoding for perforin or excretory granules of natural killer (NK) cells of CD8-lymphocytes. sHLH is also known as macrophage activation syndrome (MAS). Macrophage activation syndrome (MAS) in adults is poorly studied. Main features are fever, hepatosplenomegaly, hepatobiliary dysfunction (HBD), coagulopathy, cytopenia of two to three cell lineages, increased triglycerides and hemophagocytosis in the bone marrow. sHLH/MAS complicates hematologic malignancies, autoimmune disorders and infections mainly of viral origin. Pathogenesis is poorly understood and it is associated with increased activation of macrophages and NK cells. An autocrine loop of interleukin (IL)-1β over-secretion leads to cytokine storm of IL-6, IL-18, ferritin, and interferon-gamma; soluble CD163 is highly increased from macrophages. The true incidence of sHLH/MAS among patients with sepsis has only been studied in the cohort of the Hellenic Sepsis Study Group. Patients meeting the Sepsis-3 criteria and who had positive HSscore or co-presence of HBD and disseminated intravascular coagulation (DIC) were classified as patients with macrophage activation-like syndrome (MALS). The frequency of MALS ranged between 3 and 4% and it was an independent entity associated with early mortality after 10 days. Ferritin was proposed as a diagnostic and surrogate biomarker. Concentrations >4,420 ng/ml were associated with diagnosis of MALS with 97.1% specificity and 98% negative predictive value. Increased ferritin was also associated with increased IL-6, IL-18, IFNγ, and sCD163 and by decreased IL-10/TNFα ratio. A drop of ferritin by 15% the first 48 h was a surrogate finding of favorable outcome. There are 10 on-going trials in adults with sHLH; two for the development of biomarkers and eight for management. Only one of them is focusing in sepsis. The acronym of the trial is PROVIDE (ClinicalTrials.gov NCT03332225) and it is a double-blind randomized clinical trial aiming to deliver to patients with septic shock treatment targeting their precise immune state. Patients diagnosed with MALS are receiving randomized treatment with placebo or the IL-1β blocker anakinra.

ObjectivesTo evaluate the efficacy and safety of ianalumab (VAY736), a B cell-depleting, B cell activating factor receptor-blocking, monoclonal antibody, in patients with active primary Sjögren’s syndrome (pSS) in a double-blind, placebo-controlled, phase II, single-centre study.MethodsPatients with pSS, EULAR Sjögren’s Syndrome Disease Activity Index (ESSDAI) ≥6, were randomised to ianalumab single infusion at either 3 mg/kg (n=6), 10 mg/kg (n=12) or placebo (n=9). Outcomes were measured blinded at baseline and weeks 6, 12, 24, and unblinded at end of study (EoS) when B cell numbers had recovered. Clinical outcomes included ESSDAI, EULAR Sjögren’s Syndrome Patient Reported Index (ESSPRI), salivary flow rate, ocular staining score, physician global assessment and patient assessments of fatigue and general quality of life. Laboratory-based measures included circulating leucocyte subsets and markers of B cell activity.ResultsA similar trend showing positive therapeutic effect by ianalumab was observed across the primary clinical outcome (ESSDAI) and all secondary clinical outcomes (ESSPRI, Multidimensional Fatigue Inventory, Short Form-36, global assessments by physician and patient) versus the placebo-treated group. Rapid and profound B cell depletion of long-lasting duration occurred after a single infusion of ianalumab at either dose. Serum Ig light chains decreased, with return to baseline levels at EoS. Changes in some clinical outcomes persisted through to EoS in the higher dose group. Adverse effects were largely limited to mild to moderate infusion reactions within 24 hours of ianalumab administration.ConclusionsOverall results in this single-dose study suggest potent and sustained B cell depletion by ianalumab could provide therapeutic benefits in patients with pSS without major side effects.

COVID-19 is a highly heterogeneous and complex medical disorder; indeed, severe COVID-19 is probably amongst the most complex of medical conditions known to medical science. While enormous strides have been made in understanding the molecular pathways involved in patients infected with coronaviruses an overarching and comprehensive understanding of the pathogenesis of COVID-19 is lacking. Such an understanding is essential in the formulation of effective prophylactic and treatment strategies. Based on clinical, proteomic, and genomic studies as well as autopsy data severe COVID-19 disease can be considered to be the connection of three basic pathologic processes, namely a pulmonary macrophage activation syndrome with uncontrolled inflammation, a complement-mediated endothelialitis together with a procoagulant state with a thrombotic microangiopathy. In addition, platelet activation with the release of serotonin and the activation and degranulation of mast cells contributes to the hyper-inflammatory state. Auto-antibodies have been demonstrated in a large number of hospitalized patients which adds to the end-organ damage and pro-thrombotic state. This paper provides a clinical overview of the major pathogenetic mechanism leading to severe COVID-19 disease.

Unlike other cells in the body, immune cells have to be able to enter and adapt to life within diverse tissues. Immune cells develop within dedicated immune system organs, such as the bone marrow, thymus and lymphoid tissues, but also inhabit other tissues, wherein they not only provide defense against infection and malignancies but also contribute to homeostatic tissue function. Because different tissues have widely divergent metabolic rates and fuel requirements, this raises interesting questions about the adaptation of immune cells in specific tissues. When immune cells take up residence in different tissues, they develop a transcriptional signature that reflects adaptation to life and function within that tissue. Genes encoding metabolic-pathway proteins are strongly represented within these signatures, reflective of the importance of metabolic adaptation to tissue residence. In this Review, we discuss the available data on the metabolic adaptation of immune cells to life in different tissue sites, within the broader framework of how functional adaptation versus maladaptation in the niche can affect tissue homeostasis. In this Review, Pearce and colleagues discuss the metabolic adaptation of immune cells to various tissues and how functional adaptation compared with maladaptation within the niche can affect tissue homeostasis.

Systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still’s disease (AOSD) are considered the same disease, but a common approach for diagnosis and management is still missing.MethodsIn May 2022, EULAR and PReS endorsed a proposal for a joint task force (TF) to develop recommendations for the diagnosis and management of sJIA and AOSD. The TF agreed during a first meeting to address four topics: similarity between sJIA and AOSD, diagnostic biomarkers, therapeutic targets and strategies and complications including macrophage activation syndrome (MAS). Systematic literature reviews were conducted accordingly.ResultsThe TF based their recommendations on four overarching principles, highlighting notably that sJIA and AOSD are one disease, to be designated by one name, Still’s disease.Fourteen specific recommendations were issued. Two therapeutic targets were defined: clinically inactive disease (CID) and remission, that is, CID maintained for at least 6 months. The optimal therapeutic strategy relies on early use of interleukin (IL-1 or IL-6 inhibitors associated to short duration glucocorticoid (GC). MAS treatment should rely on high-dose GCs, IL-1 inhibitors, ciclosporin and interferon-γ inhibitors. A specific concern rose recently with cases of severe lung disease in children with Still’s disease, for which T cell directed immunosuppressant are suggested. The recommendations emphasised the key role of expert centres for difficult-to-treat patients. All overarching principles and recommendations were agreed by over 80% of the TF experts with a high level of agreement.ConclusionThese recommendations are the first consensus for the diagnosis and management of children and adults with Still’s disease.

COVID-19 infection has a heterogenous disease course; it may be asymptomatic or causes only mild symptoms in the majority of the cases, while immunologic complications such as macrophage activation syndrome also known as secondary hemophagocytic lymphohistiocytosis, resulting in cytokine storm syndrome and acute respiratory distress syndrome, may also occur in some patients. According to current literature, impairment of SARS-CoV-2 clearance due to genetic and viral features, lower levels of interferons, increased neutrophil extracellular traps, and increased pyroptosis and probable other unknown mechanisms create a background for severe disease course complicated by macrophage activation syndrome and cytokine storm. Various genetic mutations may also constitute a risk factor for severe disease course and occurrence of cytokine storm in COVID-19. Once, immunologic complications like cytokine storm occur, anti-viral treatment alone is not enough and should be combined with appropriate anti-inflammatory treatment. Anti-rheumatic drugs, which are tried for managing immunologic complications of COVID-19 infection, will also be discussed including chloroquine, hydroxychloroquine, JAK inhibitors, IL-6 inhibitors, IL-1 inhibitors, anti-TNF-α agents, corticosteroids, intravenous immunoglobulin (IVIG), and colchicine. Early recognition and appropriate treatment of immunologic complications will decrease the morbidity and mortality in COVID-19 infection, which requires the collaboration of infectious disease, lung, and intensive care unit specialists with other experts such as immunologists, rheumatologists, and hematologists.

BACKGROUNDPediatric SARS-CoV-2 infection can be complicated by a dangerous hyperinflammatory condition termed multisystem inflammatory syndrome in children (MIS-C). The clinical and immunologic spectrum of MIS-C and its relationship to other inflammatory conditions of childhood have not been studied in detail.METHODSWe retrospectively studied confirmed cases of MIS-C at our institution from March to June 2020. The clinical characteristics, laboratory studies, and treatment response were collected. Data were compared with historic cohorts of Kawasaki disease (KD) and macrophage activation syndrome (MAS).RESULTSTwenty-eight patients fulfilled the case definition of MIS-C. Median age at presentation was 9 years (range: 1 month to 17 years); 50% of patients had preexisting conditions. All patients had laboratory confirmation of SARS-CoV-2 infection. Seventeen patients (61%) required intensive care, including 7 patients (25%) who required inotrope support. Seven patients (25%) met criteria for complete or incomplete KD, and coronary abnormalities were found in 6 cases. Lymphopenia, thrombocytopenia, and elevation in inflammatory markers, D-dimer, B-type natriuretic peptide, IL-6, and IL-10 levels were common but not ubiquitous. Cytopenias distinguished MIS-C from KD and the degree of hyperferritinemia and pattern of cytokine production differed between MIS-C and MAS. Immunomodulatory therapy given to patients with MIS-C included intravenous immune globulin (IVIG) (71%), corticosteroids (61%), and anakinra (18%). Clinical and laboratory improvement were observed in all cases, including 6 cases that did not require immunomodulatory therapy. No mortality was recorded in this cohort.CONCLUSIONMIS-C encompasses a broad phenotypic spectrum with clinical and laboratory features distinct from KD and MAS.FUNDINGThis work was supported by the National Institutes of Health, National Institute of Arthritis and Musculoskeletal and Skin Diseases; the National Institute of Allergy and Infectious Diseases; Rheumatology Research Foundation Investigator Awards and Medical Education Award; Boston Children's Hospital Faculty Career Development Awards; the McCance Family Foundation; and the Samara Jan Turkel Center.

Background A subanalysis of a randomized clinical trial indicated sepsis survival benefit from interleukin (IL)-1 blockade in patients with features of the macrophage activation-like syndrome (MALS). This study aimed to investigate the frequency of MALS and to develop a biomarker of diagnosis and prognosis. Methods Patients with infections and systemic inflammatory response syndrome were assigned to one test cohort ( n  = 3417) and a validation cohort ( n  = 1704). MALS was diagnosed for patients scoring positive either for the hemophagocytic syndrome score and/or having both hepatobiliary dysfunction and disseminated intravascular coagulation. Logistic regression analysis was used to estimate the predictive value of MALS for 10-day mortality in both cohorts. Ferritin, sCD163, IL-6, IL-10, IL-18, interferon gamma (IFN-γ), and tumor necrosis factor alpha (TNF-α) were measured in the blood the first 24 h; ferritin measurements were repeated in 747 patients on day 3. Results The frequency of MALS was 3.7% and 4.3% in the test and the validation cohort, respectively. In both cohorts, MALS was an independent risk factor for 10-day mortality. A ferritin level above 4420 ng/ml was accompanied by 66.7% and 66% mortality after 28 days, respectively. Ferritin levels above 4420 ng/ml were associated with an increase of IL-6, IL-18, INF-γ, and sCD163 and a decreased IL-10/TNF-α ratio, indicating predominance of pro-inflammatory phenomena. Any less than 15% decrease of ferritin on day 3 was associated with more than 90% sensitivity for unfavorable outcome after 10 days. This high mortality risk was also validated in an independent Swedish cohort ( n  = 109). Conclusions MALS is an independent life-threatening entity in sepsis. Ferritin measurements can provide early diagnosis of MALS and may allow for specific treatment.

Heparin-induced thrombocytopenia/thrombosis (HIT) is a serious immune reaction to heparins, characterized by thrombocytopenia and often severe thrombosis with high morbidity and mortality. HIT is mediated by IgG antibodies against heparin/platelet factor 4 antigenic complexes. These complexes are thought to activate platelets leading to thrombocytopenia and thrombosis. Here we show that HIT immune complexes induce NETosis via interaction with FcγRIIa on neutrophils and through neutrophil-platelet association. HIT immune complexes induce formation of thrombi containing neutrophils, extracellular DNA, citrullinated histone H3 and platelets in a microfluidics system and in vivo, while neutrophil depletion abolishes thrombus formation. Absence of PAD4 or PAD4 inhibition with GSK484 abrogates thrombus formation but not thrombocytopenia, suggesting they are induced by separate mechanisms. NETs markers and neutrophils undergoing NETosis are present in HIT patients. Our findings demonstrating the involvement of NETosis in thrombosis will modify the current concept of HIT pathogenesis and may lead to new therapeutic strategies. The pathogenesis of heparin-induced thrombocytopenia and thrombosis (HIT) is mediated by heparin-reactive autoantibodies binding to platelets (thrombocytes). Here the authors show neutrophil activation and NETosis are elevated in patients with HIT, and are essential for thrombosis in HIT mouse models.