PD-L1- and IL-4-expressing basophils promote pathogenic accumulation of T follicular helper cells in lupus.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by anti-nuclear autoantibodies whose production is promoted by autoreactive T follicular helper (TFH) cells. During SLE pathogenesis, basophils accumulate in secondary lymphoid organs (SLO), amplify autoantibody production and disease progression through mechanisms that remain to be defined. Here, we provide evidence for a direct functional relationship between TFH cells and basophils during lupus pathogenesis, both in humans and mice. PD-L1 upregulation on basophils and IL-4 production are associated with TFH and TFH2 cell expansions and with disease activity. Pathogenic TFH cell accumulation, maintenance, and function in SLO were dependent on PD-L1 and IL-4 in basophils, which induced a transcriptional program allowing TFH2 cell differentiation and function. Our study establishes a direct mechanistic link between basophils and TFH cells in SLE that promotes autoantibody production and lupus nephritis.

Cross-Comparison of Inflammatory Skin Disease Transcriptomics Identifies PTEN as a Pathogenic Disease Classifier in Cutaneous Lupus Erythematosus.

Tissue transcriptomics is used to uncover molecular dysregulations underlying diseases. However, the majority of transcriptomics studies focus on single diseases with limited relevance for understanding the molecular relationship between diseases or for identifying disease-specific markers. In this study, we used a normalization approach to compare gene expression across nine inflammatory skin diseases. The normalized datasets were found to retain differential expression signals that allowed unsupervised disease clustering and identification of disease-specific gene signatures. Using the NS-Forest algorithm, we identified a minimal set of biomarkers and validated their use as diagnostic disease classifier. Among them, PTEN was identified as being a specific marker for cutaneous lupus erythematosus and found to be strongly expressed by lesional keratinocytes in association with pathogenic type I IFNs. In fact, PTEN facilitated the expression of IFN-ß and IFN-κ in keratinocytes by promoting activation and nuclear translocation of IRF3. Thus, cross-comparison of tissue transcriptomics is a valid strategy to establish a molecular disease classification and to identify pathogenic disease biomarkers.

Differentiation of IL-26+ TH17 intermediates into IL-17A producers via epithelial crosstalk in psoriasis.

Interleukin (IL)-26 is a TH17 cytokine with known antimicrobial and pro-inflammatory functions. However, the precise role of IL-26 in the context of pathogenic TH17 responses is unknown. Here we identify a population of blood TH17 intermediates that produce high levels of IL-26 and differentiate into IL-17A-producing TH17 cells upon TGF-ß1 exposure. By combining single cell RNA sequencing, TCR sequencing and spatial transcriptomics we show that this process occurs in psoriatic skin. In fact, IL-26+ TH17 intermediates infiltrating psoriatic skin induce TGF-ß1 expression in basal keratinocytes and thereby promote their own differentiation into IL-17A-producing cells. Thus, our study identifies IL-26-producing cells as an early differentiation stage of TH17 cells that infiltrates psoriatic skin and controls its own maturation into IL17A-producing TH17 cells, via epithelial crosstalk involving paracrine production of TGF-ß1.

The cGAS-STING pathway drives type I IFN immunopathology in COVID-19.

COVID-19, which is caused by infection with SARS-CoV-2, is characterized by lung pathology and extrapulmonary complications1,2. Type I interferons (IFNs) have an essential role in the pathogenesis of COVID-19 (refs 3-5). Although rapid induction of type I IFNs limits virus propagation, a sustained increase in the levels of type I IFNs in the late phase of the infection is associated with aberrant inflammation and poor clinical outcome5-17. Here we show that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, which controls immunity to cytosolic DNA, is a critical driver of aberrant type I IFN responses in COVID-19 (ref. 18). Profiling COVID-19 skin manifestations, we uncover a STING-dependent type I IFN signature that is primarily mediated by macrophages adjacent to areas of endothelial cell damage. Moreover, cGAS-STING activity was detected in lung samples from patients with COVID-19 with prominent tissue destruction, and was associated with type I IFN responses. A lung-on-chip model revealed that, in addition to macrophages, infection with SARS-CoV-2 activates cGAS-STING signalling in endothelial cells through mitochondrial DNA release, which leads to cell death and type I IFN production. In mice, pharmacological inhibition of STING reduces severe lung inflammation induced by SARS-CoV-2 and improves disease outcome. Collectively, our study establishes a mechanistic basis of pathological type I IFN responses in COVID-19 and reveals a principle for the development of host-directed therapeutics.

Basophils and IgE contribute to mixed connective tissue disease development.

BACKGROUND: Mixed connective tissue disease (MCTD) is a rare and complex autoimmune disease that presents mixed features with other connective tissue diseases, such as systemic lupus erythematosus, systemic sclerosis, and myositis. It is characterized by high levels of anti-U1 small nuclear ribonucleoprotein 70k autoantibodies and a high incidence of life-threatening pulmonary involvement. The pathophysiology of MCTD is not well understood, and no specific treatment is yet available for the patients. Basophils and IgE play a role in the development of systemic lupus erythematosus and thus represent new therapeutic targets for systemic lupus erythematosus and other diseases involving basophils and IgE in their pathogenesis. OBJECTIVE: We sought to investigate the role of basophils and IgE in the pathophysiology of MCTD. METHODS: Basophil activation status and the presence of autoreactive IgE were assessed in peripheral blood of a cohort of patients with MCTD and in an MCTD-like mouse model. Basophil depletion and IgE-deficient animals were used to investigate the contribution of basophils and IgE in the lung pathology development of this mouse model. RESULTS: Patients with MCTD have a peripheral basopenia and activated blood basophils overexpressing C-C chemokine receptor 3. Autoreactive IgE raised against the main MCTD autoantigen U1 small nuclear ribonucleoprotein 70k were found in nearly 80% of the patients from the cohort. Basophil activation and IgE anti-U1 small nuclear ribonucleoprotein 70k were also observed in the MCTD-like mouse model along with basophil accumulation in lymph nodes and lungs. Basophil depletion dampened lung pathology, and IgE deficiency prevented its development. CONCLUSIONS: Basophils and IgE contribute to MCTD pathophysiology and represent new candidate therapeutic targets for patients with MCTD.

Effects of BAFF Neutralization on Atherosclerosis Associated With Systemic Lupus Erythematosus.

OBJECTIVE: Cardiovascular disease (CVD) is the leading cause of death in systemic lupus erythematosus (SLE). B cells play a key role in the pathogenesis of lupus, and anti-BAFF therapy has been approved for use in SLE. Since mature B cells also promote atherosclerosis, we undertook this study to evaluate, in a mouse model and in SLE patients, whether BAFF neutralization has an atheroprotective effect in SLE. METHODS: The effect of BAFF on atherosclerosis associated with lupus was investigated in the atherosclerosis/lupus-prone apolipoprotein E-knockout D227K mouse model and in a cohort of SLE patients. Mice were treated with a blocking anti-BAFF monoclonal antibody (mAb), while fed a standard chow diet. Carotid plaque and carotid intima-media thickness were assessed by ultrasound at baseline and during follow-up in SLE patients who were asymptomatic for CVD. RESULTS: Anti-BAFF mAb in ApoE-/- D227K mice induced B cell depletion, efficiently treated lupus, and improved atherosclerosis lesions (21% decrease; P = 0.007) in mice with low plasma cholesterol levels but worsened the lesions (17% increase; P = 0.06) in mice with high cholesterol levels. The atheroprotective effect of the BAFF-BAFF receptor signaling inhibition on B cells was counterbalanced by the proatherogenic effect of the BAFF-TACI signaling inhibition on macrophages. In SLE patients, blood BAFF levels were associated with subclinical atherosclerosis (r = 0.26, P = 0.03). Anti-BAFF mAb treatment had a differential effect on the intima-media thickness progression in SLE patients depending on body mass index. CONCLUSION: Depending on the balance between lipid-induced and B cell-induced proatherogenic conditions, anti-BAFF could be detrimental or beneficial, respectively, to atherosclerosis development in SLE.

Highly sensitive serum cardiac troponin T and cardiovascular events in patients with systemic lupus erythematosus (TROPOPLUS study).

OBJECTIVE: Identification of biological markers able to better stratify cardiovascular risks in SLE patients is needed. We aimed to determine whether serum cardiac troponin T (cTnT) levels measured with a highly sensitive assay [high sensitivity cTnT (HS-cTnT)] may predict cardiovascular events (CVEs) in SLE. METHOD: All SLE patients included between 2007 and 2010 in the randomized, double-blind, placebo-controlled, multicentre PLUS trial were screened. Patients with no past history of CVE at inclusion and a follow-up period of >20 months were analysed. HS-cTnT concentration was measured using the electrochemiluminescence method on serum collected at PLUS inclusion. The primary outcome was the incident CVE. Factors associated with the primary outcome were identified and multivariate analysis was performed. RESULTS: Overall, 442 SLE patients (of the 573 included in the PLUS study) were analysed for the primary outcome with a median follow up of 110 (interquartile range: 99-120) months. Among them, 29 (6.6%) experienced at least one CVE that occurred at a median of 67 (interquartile range: 31-91) months after inclusion. Six out of 29 patients had more than one CVE. In the multivariate analysis, dyslipidaemia, age and HS-cTnT were associated with the occurrence of CVE. Kaplan-Meier analysis showed that a concentration of HS-cTnT > 4.27 ng/l at inclusion increased by 2.7 [hazard ratio 2.7 (95% CI: 1.3, 5.6), P =0.0083] the risk of CVE in SLE. CONCLUSION: HS-cTnT measured in serum is the first identified biomarker independently associated with incident CVE in SLE patients.

Prostaglandin D2 amplifies lupus disease through basophil accumulation in lymphoid organs.

In systemic lupus erythematosus (SLE), autoantibody production can lead to kidney damage and failure, known as lupus nephritis. Basophils amplify the synthesis of autoantibodies by accumulating in secondary lymphoid organs. Here, we show a role for prostaglandin D2 (PGD2) in the pathophysiology of SLE. Patients with SLE have increased expression of PGD2 receptors (PTGDR) on blood basophils and increased concentration of PGD2 metabolites in plasma. Through an autocrine mechanism dependent on both PTGDRs, PGD2 induces the externalization of CXCR4 on basophils, both in humans and mice, driving accumulation in secondary lymphoid organs. Although PGD2 can accelerate basophil-dependent disease, antagonizing PTGDRs in mice reduces lupus-like disease in spontaneous and induced mouse models. Our study identifies the PGD2/PTGDR axis as a ready-to-use therapeutic modality in SLE.

Basophils contribute to pristane-induced Lupus-like nephritis model.

Lupus nephritis (LN), one of the most severe outcomes of systemic lupus erythematosus (SLE), is initiated by glomerular deposition of immune-complexes leading to an inflammatory response and kidney failure. Autoantibodies to nuclear antigens and autoreactive B and T cells are central in SLE pathogenesis. Immune mechanisms amplifying this autoantibody production drive flares of the disease. We previously showed that basophils were contributing to LN development in a spontaneous lupus-like mouse model (constitutive Lyn -/- mice) and in SLE subjects through their activation and migration to secondary lymphoid organs (SLOs) where they amplify autoantibody production. In order to study the basophil-specific mechanisms by which these cells contribute to LN development, we needed to validate their involvement in a genetically independent SLE-like mouse model. Pristane, when injected to non-lupus-prone mouse strains, induces a LN-like disease. In this inducible model, basophils were activated and accumulated in SLOs to promote autoantibody production. Basophil depletion by two distinct approaches dampened LN-like disease, demonstrating their contribution to the pristane-induced LN model. These results enable further studies to decipher molecular mechanisms by which basophils contribute to lupus progression.