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Upon sensing cytosolic DNA, the enzyme cGAS induces innate immune responses that underpin anti-microbial defenses and certain autoimmune diseases. Missense mutations of PRKDC encoding the DNA-dependent protein kinase (DNA-PK) catalytic subunit (DNA-PKcs) are associated with autoimmune diseases, yet how DNA-PK deficiency leads to increased immune responses remains poorly understood. In this study, we report that DNA-PK phosphorylates cGAS and suppresses its enzymatic activity. DNA-PK deficiency reduces cGAS phosphorylation and promotes antiviral innate immune responses, thereby potently restricting viral replication. Moreover, cells isolated from DNA-PKcs-deficient mice or patients carrying PRKDC missense mutations exhibit an inflammatory gene expression signature. This study provides a rational explanation for the autoimmunity of patients with missense mutations of PRKDC , and suggests that cGAS-mediated immune signaling is a potential target for therapeutic interventions. The enzyme cGAS induces innate immune responses upon recognition of cytosolic DNA. Here, using in vitro and in vivo models, the authors identify DNA-PK as a negative regulator of cGAS signalling.

Autoimmunity can occur when a checkpoint of self-tolerance fails. The study of familial autoimmune diseases can reveal pathophysiological mechanisms involved in more common autoimmune diseases. Here, by whole-exome/genome sequencing we identify heterozygous, autosomal-dominant, germline loss-of-function mutations in the SOCS1 gene in ten patients from five unrelated families with early onset autoimmune manifestations. The intracellular protein SOCS1 is known to downregulate cytokine signaling by inhibiting the JAK-STAT pathway. Accordingly, patient-derived lymphocytes exhibit increased STAT activation in vitro in response to interferon-γ, IL-2 and IL-4 that is reverted by the JAK1/JAK2 inhibitor ruxolitinib. This effect is associated with a series of in vitro and in vivo immune abnormalities consistent with lymphocyte hyperactivity. Hence, SOCS1 haploinsufficiency causes a dominantly inherited predisposition to early onset autoimmune diseases related to cytokine hypersensitivity of immune cells. SOCS1 is a potent suppressor of JAK-STAT signalling responses to IFNγ and γ-chain cytokines and thereby limits inflammation. Here the authors identify and characterize heterozygous SOCS1 mutations in 10 patients from 5 unrelated families with autoimmune diseases.

Type I and III interferons (IFN-I/λ) are important antiviral mediators against SARS-CoV-2 infection. Here, we demonstrate that plasmacytoid dendritic cells (pDC) are the predominant IFN-I/λ source following their sensing of SARS-CoV-2-infected cells. Mechanistically, this short-range sensing by pDCs requires sustained integrin-mediated cell adhesion with infected cells. In turn, pDCs restrict viral spread by an IFN-I/λ response directed toward SARS-CoV-2-infected cells. This specialized function enables pDCs to efficiently turn-off viral replication, likely via a local response at the contact site with infected cells. By exploring the pDC response in SARS-CoV-2 patients, we further demonstrate that pDC responsiveness inversely correlates with the severity of the disease. The pDC response is particularly impaired in severe COVID-19 patients. Overall, we propose that pDC activation is essential to control SARS-CoV-2-infection. Failure to develop this response could be important to understand severe cases of COVID-19. Plasmacytoid DC (pDC) have been shown to secrete type I IFN and to be involved in controlling replication and spread of some viruses. Here the authors show that in severe SARS-CoV-2 infection pDC function is impaired leading to reduced type I IFN production and possibly lower viral control.

The genetic encephalopathy Aicardi–Goutières syndrome is thought to be due to misidentification of self-derived nucleic acids and the induction of a type I interferon–mediated response. Administration of three reverse-transcriptase inhibitors reduced interferon signaling and serum levels of interferon in patients with the syndrome.

Background Our study aimed to provide real-world evidence on the treatment patterns, effectiveness and safety of canakinumab in France in Familial Mediterranean Fever (FMF), Mevalonate Kinase Deficiency (MKD), and Tumor necrosis factor Receptor Associated Periodic Syndrome (TRAPS). Methods This study used the JIR cohort, a multicentre international registry created in 2013 to collect data on patients with juvenile inflammatory rheumatic diseases. French patients diagnosed with FMF, MKD or TRAPS and treated with canakinumab were included in this study. Results 31 FMF, 26 MKD and 7 TRAPS patients received canakinumab during the study period. Most of them initiated canakinumab at the recommended dose of 2 mg/kg or 150 mg, but less than half of FMF and MKD patients initiated it at the recommended frequency (every 4 weeks). Two years after initiation, the rate of patients still on treatment was 78.1% in FMF, 73.7% in MKD, and 85.7% in TRAPS patients. While the dose per injection remained globally the same over the course of the treatment, some adjustments of the dose intervals were observed. Six patients had a severe adverse event reported. Of those, three were possibly related to canakinumab. Conclusion This interim analysis showed a good maintenance of canakinumab treatment 2 years after initiation and confirmed its safety profile in real-life practice in France in patients diagnosed with FMF, MKD and TRAPS. The high variety of dose and interval combinations observed in canakinumab treated patients let suppose that physicians adapt the posology to individual situations rather than a fixed treatment plan.

Objectives To validate the previously proposed classification criteria for Henoch–Schönlein purpura (HSP), childhood polyarteritis nodosa (c-PAN), c-Wegener granulomatosis (c-WG) and c-Takayasu arteritis (c-TA). Methods Step 1: retrospective/prospective web-data collection for children with HSP, c-PAN, c-WG and c-TA with age at diagnosis ≤18 years. Step 2: blinded classification by consensus panel of a representative sample of 280 cases. Step 3: statistical (sensitivity, specificity, area under the curve and κ-agreement) and nominal group technique consensus evaluations. Results 827 patients with HSP, 150 with c-PAN, 60 with c-WG, 87 with c-TA and 52 with c-other were compared with each other. A patient was classified as HSP in the presence of purpura or petechiae (mandatory) with lower limb predominance plus one of four criteria: (1) abdominal pain; (2) histopathology (IgA); (3) arthritis or arthralgia; (4) renal involvement. Classification of c-PAN required a systemic inflammatory disease with evidence of necrotising vasculitis OR angiographic abnormalities of medium-/small-sized arteries (mandatory criterion) plus one of five criteria: (1) skin involvement; (2) myalgia/muscle tenderness; (3) hypertension; (4) peripheral neuropathy; (5) renal involvement. Classification of c-WG required three of six criteria: (1) histopathological evidence of granulomatous inflammation; (2) upper airway involvement; (3) laryngo-tracheo-bronchial involvement; (4) pulmonary involvement (x-ray/CT); (5) antineutrophilic cytoplasmic antibody positivity; (6) renal involvement. Classification of c-TA required typical angiographic abnormalities of the aorta or its main branches and pulmonary arteries (mandatory criterion) plus one of five criteria: (1) pulse deficit or claudication; (2) blood pressure discrepancy in any limb; (3) bruits; (4) hypertension; (5) elevated acute phase reactant. Conclusion European League Against Rheumatism/Paediatric Rheumatology International Trials Organisation/Paediatric Rheumatology European Society propose validated classification criteria for HSP, c-PAN, c-WG and c-TA with high sensitivity/specificity.

Background Inborn errors of immunity (IEI) and autoantibodies to type I interferons (IFNs) underlie critical COVID-19 pneumonia in at least 15% of the patients, while the causes of multisystem inflammatory syndrome in children (MIS-C) remain elusive. Objectives To detect causal genetic variants in very rare cases with concomitant critical COVID-19 pneumonia and MIS-C. Methods Whole exome sequencing was performed, and the impact of candidate gene variants was investigated. Plasma levels of cytokines, specific antibodies against the virus, and autoantibodies against type I IFNs were also measured. Results We report a 3-year-old child who died on day 56 of SARS-CoV-2 infection with an unusual clinical presentation, combining both critical COVID-19 pneumonia and MIS-C. We identified a large, homozygous loss-of-function deletion in IFNAR1 , underlying autosomal recessive IFNAR1 deficiency. Conclusions Our findings confirm that impaired type I IFN immunity can underlie critical COVID-19 pneumonia, while suggesting that it can also unexpectedly underlie concomitant MIS-C. Our report further raises the possibility that inherited or acquired dysregulation of type I IFN immunity might contribute to MIS-C in other patients.

Systemic sclerosis (SSc) is a generalized disease of the connective tissue, arterioles, and microvessels, characterized by the appearance of fibrosis and vascular obliteration. There are two main phenotypical forms of SSc: a diffuse cutaneous form that extends towards the proximal region of the limbs and/or torso, and a limited cutaneous form where the cutaneous sclerosis only affects the extremities of the limbs (without passing beyond the elbows and knees). There also exists in less than 10% of cases forms that never involve the skin. This is called SSc sine scleroderma. The prognosis depends essentially on the occurrence of visceral damage and more particularly interstitial lung disease (which is sometimes severe), pulmonary arterial hypertension, or primary cardiac damage, which represent the three commonest causes of mortality in SSc. Another type of involvement with poor prognosis, scleroderma renal crisis, is rare (less than 5% of cases). Cutaneous extension is also an important parameter, with the diffuse cutaneous forms having less favorable prognosis.

Chimeric antigen receptor (CAR) T-cell therapy targeting B cells has shown promising results, including drug-free remission, in adult-onset autoimmune diseases. Extending this therapeutic approach to the pediatric population, particularly for juvenile autoimmune diseases, presents an exciting opportunity. However, challenges specific to juvenile-onset autoimmune conditions, such as long-term adverse events, heightened disease activity, and the imperative to reduce steroid exposure, must be considered. While this strategy appears viable for these severe conditions, the limited data available for this population and the absence of evidence on cases with a high genetic component, such as monogenic lupus, represent significant challenges. Most monogenic lupus cases are associated with innate immune defects, and the involvement of B cells in these genetic anomalies remains poorly understood. In this review, we examine the potential indications, current knowledge, and limitations of CAR-T cell therapy in juvenile-onset autoimmune diseases, extending the discussion beyond early-onset lupus.

Aicardi-Goutières syndrome (AGS) is a genetic type I interferon (IFN)-mediated disease characterized by neurological involvement with onset in utero or in childhood. Here, we analyze peripheral blood samples from patients bearing AGS-causing mutations in ADAR1, RNASEH2B or SAMHD1 using single-cell transcriptomics and targeted metabolomics. Using machine-learning approaches and differential gene expression analysis, we identified a loss of transcription factor hypoxia induced factor 1 α (HIF-1α) expression and activity associated with features of a metabolic switch favoring oxidative phosphorylation and glutathione metabolism over glycolysis in monocytes and dendritic cells. Evidences of mitochondrial stress and accumulation of cytosolic double-stranded DNA and RNA were also found. The energy metabolic switch was confirmed at the metabolic level in primary peripheral blood mononuclear cells of AGS patients. Chemical stabilization of HIF-1α using a synthetic drug in in vitro cellular models of AGS, reversed the energy metabolic switch towards glycolysis, attenuated mitochondrial stress, and markedly reduced the IFN response and IP-10 production. We therefore propose that an energy metabolic switch contributes to chronic inflammation in AGS and that targeting this pathway might represent a potential therapeutic approach. Aicardi-Goutières syndrome (AGS) is a brain condition characterized by type I interferon (IFN)-mediated inflammation. Here, the authors demonstrate a negative correlation between the metabolic regulator, HIF-1α, and type-I IFN responses in AGS.