Biallelic human SHARPIN loss of function induces autoinflammation and immunodeficiency.

The linear ubiquitin assembly complex (LUBAC) consists of HOIP, HOIL-1 and SHARPIN and is essential for proper immune responses. Individuals with HOIP and HOIL-1 deficiencies present with severe immunodeficiency, autoinflammation and glycogen storage disease. In mice, the loss of Sharpin leads to severe dermatitis due to excessive keratinocyte cell death. Here, we report two individuals with SHARPIN deficiency who manifest autoinflammatory symptoms but unexpectedly no dermatological problems. Fibroblasts and B cells from these individuals showed attenuated canonical NF-κB responses and a propensity for cell death mediated by TNF superfamily members. Both SHARPIN-deficient and HOIP-deficient individuals showed a substantial reduction of secondary lymphoid germinal center B cell development. Treatment of one SHARPIN-deficient individual with anti-TNF therapies led to complete clinical and transcriptomic resolution of autoinflammation. These findings underscore the critical function of the LUBAC as a gatekeeper for cell death-mediated immune dysregulation in humans.

The Aconitate Decarboxylase 1/Itaconate Pathway Modulates Immune Dysregulation and Associates with Cardiovascular Disease Markers and Disease Activity in Systemic Lupus Erythematosus.

The Krebs cycle enzyme aconitate decarboxylase 1 (ACOD1) mediates itaconate synthesis in monocytes and macrophages. Previously, we reported that administration of 4-octyl itaconate to lupus-prone mice abrogated immune dysregulation and clinical features. In this study, we explore the role of the endogenous ACOD1/itaconate pathway in the development of TLR7-induced lupus (imiquimod [IMQ] model). We found that, in vitro, ACOD1 was induced in mouse bone marrow-derived macrophages and human monocyte-derived macrophages following TLR7 stimulation. This induction was partially dependent on type I IFN receptor signaling and on specific intracellular pathways. In the IMQ-induced mouse model of lupus, ACOD1 knockout (Acod1-/-) displayed disruptions of the splenic architecture, increased serum levels of anti-dsDNA and proinflammatory cytokines, and enhanced kidney immune complex deposition and proteinuria, when compared with the IMQ-treated wild-type mice. Consistent with these results, Acod1-/- bone marrow-derived macrophages treated in vitro with IMQ showed higher proinflammatory features. Furthermore, itaconate serum levels in systemic lupus erythematosus patients were decreased compared with healthy individuals, in association with disease activity and specific perturbed cardiometabolic parameters. These findings suggest that the ACOD1/itaconate pathway plays important immunomodulatory and vasculoprotective roles in systemic lupus erythematosus, supporting the potential therapeutic role of itaconate analogs in autoimmune diseases.

Somatic Mutations in UBA1 and Severe Adult-Onset Autoinflammatory Disease.

BACKGROUND: Adult-onset inflammatory syndromes often manifest with overlapping clinical features. Variants in ubiquitin-related genes, previously implicated in autoinflammatory disease, may define new disorders. METHODS: We analyzed peripheral-blood exome sequence data independent of clinical phenotype and inheritance pattern to identify deleterious mutations in ubiquitin-related genes. Sanger sequencing, immunoblotting, immunohistochemical testing, flow cytometry, and transcriptome and cytokine profiling were performed. CRISPR-Cas9-edited zebrafish were used as an in vivo model to assess gene function. RESULTS: We identified 25 men with somatic mutations affecting methionine-41 (p.Met41) in UBA1, the major E1 enzyme that initiates ubiquitylation. (The gene UBA1 lies on the X chromosome.) In such patients, an often fatal, treatment-refractory inflammatory syndrome develops in late adulthood, with fevers, cytopenias, characteristic vacuoles in myeloid and erythroid precursor cells, dysplastic bone marrow, neutrophilic cutaneous and pulmonary inflammation, chondritis, and vasculitis. Most of these 25 patients met clinical criteria for an inflammatory syndrome (relapsing polychondritis, Sweet's syndrome, polyarteritis nodosa, or giant-cell arteritis) or a hematologic condition (myelodysplastic syndrome or multiple myeloma) or both. Mutations were found in more than half the hematopoietic stem cells, including peripheral-blood myeloid cells but not lymphocytes or fibroblasts. Mutations affecting p.Met41 resulted in loss of the canonical cytoplasmic isoform of UBA1 and in expression of a novel, catalytically impaired isoform initiated at p.Met67. Mutant peripheral-blood cells showed decreased ubiquitylation and activated innate immune pathways. Knockout of the cytoplasmic UBA1 isoform homologue in zebrafish caused systemic inflammation. CONCLUSIONS: Using a genotype-driven approach, we identified a disorder that connects seemingly unrelated adult-onset inflammatory syndromes. We named this disorder the VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. (Funded by the NIH Intramural Research Programs and the EU Horizon 2020 Research and Innovation Program.).

Interferon lambda promotes immune dysregulation and tissue inflammation in TLR7-induced lupus.

Type III IFN lambdas (IFN-λ) have recently been described as important mediators of immune responses at barrier surfaces. However, their role in autoimmune diseases such as systemic lupus erythematosus (SLE), a condition characterized by aberrant type I IFN signaling, has not been determined. Here, we identify a nonredundant role for IFN-λ in immune dysregulation and tissue inflammation in a model of TLR7-induced lupus. IFN-λ protein is increased in murine lupus and IFN-λ receptor (Ifnlr1) deficiency significantly reduces immune cell activation and associated organ damage in the skin and kidneys without effects on autoantibody production. Single-cell RNA sequencing in mouse spleen and human peripheral blood revealed that only mouse neutrophils and human B cells are directly responsive to this cytokine. Rather, IFN-λ activates keratinocytes and mesangial cells to produce chemokines that induce immune cell recruitment and promote tissue inflammation. These data provide insights into the immunobiology of SLE and identify type III IFNs as important factors for tissue-specific pathology in this disease.

Sex differences in neutrophil biology modulate response to type I interferons and immunometabolism.

Differences between female and male immunity may contribute to variations in response to infections and predisposition to autoimmunity. We previously reported that neutrophils from reproductive-age males are more immature and less activated than their female counterparts. To further characterize the mechanisms that drive differential neutrophil phenotypes, we performed RNA sequencing on circulating neutrophils from healthy adult females and males. Female neutrophils displayed significant up-regulation of type I IFN (IFN)-stimulated genes (ISGs). Single-cell RNA-sequencing analysis indicated that these differences are neutrophil specific, driven by a distinct neutrophil subset and related to maturation status. Neutrophil hyperresponsiveness to type I IFNs promoted enhanced responses to Toll-like receptor agonists. Neutrophils from young adult males had significantly increased mitochondrial metabolism compared to those from females and this was modulated by estradiol. Assessment of ISGs and neutrophil maturation genes in Klinefelter syndrome (47, XXY) males and in prepubescent children supported that differences in neutrophil phenotype between adult male and female neutrophils are hormonally driven and not explained by X chromosome gene dosage. Our results indicate that there are distinct sex differences in neutrophil biology related to responses to type I IFNs, immunometabolism, and maturation status that may have prominent functional and pathogenic implications.

Transcriptomic, epigenetic, and functional analyses implicate neutrophil diversity in the pathogenesis of systemic lupus erythematosus.

Neutrophil dysregulation is implicated in the pathogenesis of systemic lupus erythematosus (SLE). SLE is characterized by elevated levels of a pathogenic neutrophil subset known as low-density granulocytes (LDGs). The origin and phenotypic, functional, and pathogenic heterogeneity of LDGs remain to be systematically determined. Transcriptomics and epigenetic assessment of lupus LDGs, autologous normal-density neutrophils, and healthy control neutrophils was performed by bulk and single-cell RNA sequencing and assay for transposase-accessible chromatin sequencing. Functional readouts were compared among neutrophil subsets. SLE LDGs display significant transcriptional and epigenetic heterogeneity and comprise 2 subpopulations of intermediate-mature and immature neutrophils, with different degrees of chromatin accessibility and differences in transcription factor motif analysis. Differences in neutrophil extracellular trap (NET) formation, oxidized mitochondrial DNA release, chemotaxis, phagocytosis, degranulation, ability to harm the endothelium, and responses to type I interferon (IFN) stimulation are evident among LDG subsets. Compared with other immune cell subsets, LDGs display the highest expression of IFN-inducible genes. Distinct LDG subsets correlate with specific clinical features of lupus and with the presence and severity of coronary artery disease. Phenotypic, functional, and pathogenic neutrophil heterogeneity are prevalent in SLE and may promote immune dysregulation and prominent vascular damage characteristic of this disease.

Amino acid signatures of HLA Class-I and II molecules are strongly associated with SLE susceptibility and autoantibody production in Eastern Asians.

Human leukocyte antigen (HLA) is a key genetic factor conferring risk of systemic lupus erythematosus (SLE), but precise independent localization of HLA effects is extremely challenging. As a result, the contribution of specific HLA alleles and amino-acid residues to the overall risk of SLE and to risk of specific autoantibodies are far from completely understood. Here, we dissected (a) overall SLE association signals across HLA, (b) HLA-peptide interaction, and (c) residue-autoantibody association. Classical alleles, SNPs, and amino-acid residues of eight HLA genes were imputed across 4,915 SLE cases and 13,513 controls from Eastern Asia. We performed association followed by conditional analysis across HLA, assessing both overall SLE risk and risk of autoantibody production. DR15 alleles HLA-DRB1*15:01 (P = 1.4x10-27, odds ratio (OR) = 1.57) and HLA-DQB1*06:02 (P = 7.4x10-23, OR = 1.55) formed the most significant haplotype (OR = 2.33). Conditioned protein-residue signals were stronger than allele signals and mapped predominantly to HLA-DRB1 residue 13 (P = 2.2x10-75) and its proxy position 11 (P = 1.1x10-67), followed by HLA-DRB1-37 (P = 4.5x10-24). After conditioning on HLA-DRB1, novel associations at HLA-A-70 (P = 1.4x10-8), HLA-DPB1-35 (P = 9.0x10-16), HLA-DQB1-37 (P = 2.7x10-14), and HLA-B-9 (P = 6.5x10-15) emerged. Together, these seven residues increased the proportion of explained heritability due to HLA to 2.6%. Risk residues for both overall disease and hallmark autoantibodies (i.e., nRNP: DRB1-11, P = 2.0x10-14; DRB1-13, P = 2.9x10-13; DRB1-30, P = 3.9x10-14) localized to the peptide-binding groove of HLA-DRB1. Enrichment for specific amino-acid characteristics in the peptide-binding groove correlated with overall SLE risk and with autoantibody presence. Risk residues were in primarily negatively charged side-chains, in contrast with rheumatoid arthritis. We identified novel SLE signals in HLA Class I loci (HLA-A, HLA-B), and localized primary Class II signals to five residues in HLA-DRB1, HLA-DPB1, and HLA-DQB1. These findings provide insights about the mechanisms by which the risk residues interact with each other to produce autoantibodies and are involved in SLE pathophysiology.

Region specificity of rheumatoid foot symptoms associated with ultrasound-detected synovitis and joint destruction.

OBJECTIVES: We aimed to clarify the clinical implication of ultrasound (US)-detected foot joint inflammation in tightly controlled patients with rheumatoid arthritis (RA). METHODS: We evaluated bilateral foot joints (second to fifth metatarsophalangeal joints of forefoot; tarsometatarsal, cuneonavicular and midtarsal joints of midfoot) of 430 RA patients for synovitis using Power Doppler (PD) imaging by US. We made a cross-sectional and a 3-year longitudinal analysis about the associations of US-detected synovitis with clinical, laboratory and radiographic data as well as foot-specific outcomes using a self-administered foot evaluation questionnaire (SAFE-Q). RESULTS: The US-detected foot synovitis was seen in 28% of patients. The US-detected synovitis was closely related to 28 joint-disease activity score (DAS28) more in the forefoot than in the midfoot, while related to joint destruction in both. Multiple regression analyses showed significant associations between midfoot PD positivity and SAFE-Q in the remission group. SAFE-Q was worsened after the 3-year interval, but PD positivity at baseline did not contribute to the changes. On the other hand, destruction of the joints with US-detected synovitis significantly progressed in 3 years than with not. CONCLUSIONS: US-detected synovitis on foot joints were related to systemic inflammation, clinical symptoms, and future joint destruction with region specificity.

Severe joint deformity and patient global assessment of disease are associated with discrepancies between sonographic and clinical remission: A cross-sectional study of rheumatoid arthritis patients.

OBJECTIVE: Although recent clinical trials showed that ultrasound (US) remission is not required to achieve good outcomes at the group level, it currently remains unclear whether the prognosis of individual patients in clinical remission, but not US remission, i.e. those with subclinical sonographic synovitis (SSS), is favorable. However, it is no longer acceptable to perform US on all patients in order to identify those with SSS. Therefore, the present study was initiated to elucidate the conditions under which SSS is frequently detected. METHODS: In total, 563 consecutive RA patients were recruited. Bilateral 2-5 MCP, wrist, ankle, and 2-5 MTP joints were scanned by US, and Gray scale and Power Doppler (PD) images were scored semi-quantitatively. Clinical data were obtained by physicians who were blind to US results. Changes in the modified Total Sharp Score (mTSS) of tocilizumab (TCZ) users were calculated. RESULTS: A total of 402 patients were included. SSS was more frequently detected in patients with more severe joint deformity, even if they were in remission. In contrast, a high Patient Global Assessment of Disease (PtGA) did not reflect SSS. Furthermore, the relationship between PtGA and PD scores was weak. Although the frequency of SSS was high in TCZ user, the presence of SSS in TCZ users not always results in the progression of mTSS. CONCLUSIONS: While remission is overestimated in patients with severe joint deformity, underestimations may occur in those who do not fulfill remission criteria because of a high PtGA.

Activated neutrophil carbamylates albumin via the release of myeloperoxidase and reactive oxygen species regardless of NETosis.

Objective: An anti-carbamylated albumin antibody was detected in rheumatoid arthritis (RA) patients, and its presence was associated with serum myeloperoxidase (MPO) levels, as we reported previously. Since MPO is a key enzyme for carbamylation and is released by neutrophil extracellular traps (NETs), we aimed to demonstrate that NETosis induces carbamylation.Methods: Human neutrophils were isolated from a healthy donor, pre-treated with or without diphenyleneiodonium (DPI, an inhibitor for the generation of reactive oxygen species (ROS)), Cl-amidine (a peptidylarginine deiminase inhibitor), 4-aminobenzoic acid hydrazide (4-ABAH, an MPO inhibitor), or GW311616A (a neutrophil elastase (NE) inhibitor), and incubated for 8 h with or without phorbol 12-myristate 13-acetate (PMA). Proteins in the medium were collected and the carbamylation of albumin was evaluated by Western blotting.Results: The carbamylation of albumin was detected in the culture medium of activated neutrophils. NETosis was observed under the stimulation by PMA. DPI and 4-ABAH inhibited the carbamylation of albumin and NETosis. GW311616A inhibited NETosis, but not carbamylation. Neither carbamylation nor NETosis was inhibited by Cl-amidine.Conclusion: Activated neutrophils may carbamylate ambient albumin, and this is dependent on ROS and MPO, but does not require NETosis.

Feasibility of patient-oriented ultrasound joint selection: Cross-sectional observational study on rheumatoid arthritis.

Objective: Ultrasonography (US) is a useful tool for evaluating the activity of rheumatoid arthritis (RA) patients. As the systemic evaluation of many joints is time-consuming, a method to evaluate this activity with a smaller number of joints is needed. The aim of this study was to clarify whether the number of joints assessed may be reduced using patient-oriented joint selection.Methods: A total of 492 RA patients were recruited at Kyoto University Hospital. Bilateral metacarpophalangeal (MCP), (proximal) interphalangeal (PIP/IP), and wrist joints were evaluated by US. Gray scale and power Doppler imaging findings were scored by a 0-3 semi-quantitative method. Clinical assessments were performed by physicians who were blind to US results, and a questionnaire on subjective symptoms was collected from each patient.Results: The correlation between the US score of all 22 joints (US22) and patient-oriented painful joints (PtUS) or physician-oriented tender and/or swollen joints were moderate (Spearman's ρ = 0.435) and weak (ρ = 0.383), respectively. These correlations were weaker than that between the total US score of 5 preselected joints (unilateral 2MCP, 3MCP, 2PIP, 3PIP, and the wrist) and US22 (ρ = 0.813). However, when focusing on patients whose painful joints were 5 and more, the correlation between PtUS and US22 was markedly stronger (ρ = 0.757).Conclusion: Patient-oriented joint selection reflected actual joint inflammation to some extent. However, excessive reductions in the number of joints assessed need to be avoided even if patients do not have arthralgia because of the potential for underestimations.

Carbamylated albumin is one of the target antigens of anti-carbamylated protein antibodies.

Objectives: Anti-carbamylated protein (anti-CarP) antibodies are detected in RA patients. Fetal calf serum is used as an antigen source in anti-CarP ELISA, and the precise target antigens have not been found. We aimed to identify the target antigens of anti-CarP antibodies. Methods: Western blotting of anti-CarP antibodies was conducted. Anti-carbamylated human albumin (CarALB) antibody was detected by in-house ELISA for 493 RA patients and 144 healthy controls (HCs). An inhibition ELISA of anti-CarP antibodies by CarALB and citrullinated albumin (citALB) was performed using eight RA patients' sera. Serum CarALB was detected by liquid chromatography-tandem mass spectroscopy (LC/MS/MS), and the serum MPO concentration was measured by ELISA. Results: We focused on carbamylated albumin because it corresponded to the size of the thickest band detected by western blotting of anti-CarP antibodies. Anti-CarALB antibody was detected in 31.4% of RA patients, and the correlation of the titres between anti-CarALB and anti-CarP was much closer than that between anti-citALB and anti-CCP antibodies (ρ = 0.59 and ρ = 0.16, respectively). The inhibition ELISA showed that anti-CarP antibodies were inhibited by CarALB, but not by citALB. CarALB was detected in sera from RA patients by LC/MS/MS. The serum MPO concentration was correlated with disease activity and was higher in RA patients with anti-CarALB antibody than in those without. Conclusion: We found that carbamylated albumin is a novel target antigen of anti-CarP antibodies, and it is the first reported target antigen that has not been reported as the target of ACPA.

The aconitate decarboxylase 1/itaconate pathway modulates immune dysregulation and associates with cardiovascular disease markers in SLE.

Objective: The Krebs cycle enzyme Aconitate Decarboxylase 1 (ACOD1) mediates itaconate synthesis in myeloid cells.. Previously, we reported that administration of 4-octyl itaconate abrogated lupus phenotype in mice. Here, we explore the role of the endogenous ACOD1/itaconate pathway in the development of murine lupus as well as their relevance in premature cardiovascular damage in SLE. Methods: We characterized Acod1 protein expression in bone marrow-derived macrophages and human monocyte-derived macrophages, following a TLR7 agonist (imiquimod, IMQ). Wild type and Acod1-/- mice were exposed to topical IMQ for 5 weeks to induce an SLE phenotype and immune dysregulation was quantified. Itaconate serum levels were quantified in SLE patients and associated to cardiometabolic parameters and disease activity. Results: ACOD1 was induced in mouse bone marrow-derived macrophages (BMDM) and human monocyte-derived macrophages following in vitro TLR7 stimulation. This induction was partially dependent on type I Interferon receptor signaling and specific intracellular pathways. In the IMQ-induced mouse model of lupus, ACOD1 knockout (Acod1-/-) displayed disruptions of the splenic architecture, increased serum anti-dsDNA and proinflammatory cytokine levels, enhanced kidney immune complex deposition and proteinuria, when compared to the IMQ-treated WT mice. Consistent with these results, Acod1-/- BMDM exposed to IMQ showed higher proinflammatory features in vitro. Itaconate levels were decreased in SLE serum compared to healthy control sera, in association with specific perturbed cardiometabolic parameters and subclinical vascular disease. Conclusion: These findings suggest that the ACOD1/itaconate pathway plays important immunomodulatory and vasculoprotective roles in SLE, supporting the potential therapeutic role of itaconate analogs in autoimmune diseases.

Real-Time High Throughput Technique to Quantify Neutrophil Extracellular Traps Formation in Human Neutrophils.

Neutrophils are myeloid-lineage cells that form a crucial part of the innate immune system. The past decade has revealed additional key roles that neutrophils play in the pathogenesis of cancer, autoimmune diseases, and various acute and chronic inflammatory conditions by contributing to the initiation and perpetuation of immune dysregulation through multiple mechanisms, including the formation of neutrophil extracellular traps (NETs), which are structures crucial in antimicrobial defense. Limitations in techniques to quantify NET formation in an unbiased, reproducible, and efficient way have restricted our ability to further understand the role of neutrophils in health and diseases. We describe an automated, real-time, high-throughput method to quantify neutrophils undergoing NET formation using a live cell imaging platform coupled with a membrane permeability-dependent dual-dye approach using two different DNA dyes to image intracellular and extracellular DNA. This methodology is able to help assess neutrophil physiology and test molecules that can target NET formation.

Quantification of Neutrophils Undergoing NET Formation and Distinguishing Mechanisms of Neutrophil Cell Death by Use of a High-Throughput Method.

Neutrophils, the most abundant white blood cell type in humans, play a crucial role in innate host defenses. Recent studies have revealed additional key roles in the pathogenesis of cancer and autoimmune diseases through multiple mechanisms including the formation of neutrophil extracellular traps (NETs). Further research to expand the understanding of neutrophils' role in health and diseases is limited by lack of techniques to quantify neutrophils undergoing NET formation in an objective, reproducible, and efficient manner. In this chapter, we describe an automated high-throughput method to quantify NETting neutrophils in real time using a two-color, live-content imaging platform, the IncuCyte™S3 (Essen BioScience, Inc.) system, coupled to membrane integrity-dependent dual-dye approach to image intracellular and extracellular DNA. Based on characteristic differences in nuclear morphology and membrane integrity, this method may also be used to distinguish between different types of neutrophil cell death. This platform can help to assess neutrophil physiology and to develop and test therapeutic targets.

Neutrophils as Drivers of Immune Dysregulation in Autoimmune Diseases with Skin Manifestations.

Dysregulation in the phenotype and function of neutrophils may play important roles in the initiation and perpetuation of autoimmune responses, including conditions affecting the skin. Neutrophils can have local and systemic effects on innate and adaptive immune cells as well as on resident cells in the skin, including keratinocytes (KCs). Aberrant formation/clearance of neutrophil extracellular traps (NETs) in systemic autoimmunity and chronic inflammatory diseases have been associated with the externalization of modified autoantigens in peripheral blood and tissues. NETs can impact the function of many cells, including macrophages, lymphocytes, dendritic cells, fibroblasts, and KCs. Emerging evidence has unveiled the pathogenic key roles of neutrophils in systemic lupus erythematosus, idiopathic inflammatory myopathies, psoriasis, hidradenitis suppurativa, and other chronic inflammatory conditions. As such, neutrophil-targeting strategies represent promising therapeutic options for these diseases.

Modulation of the Itaconate Pathway Attenuates Murine Lupus.

OBJECTIVE: Itaconic acid, a Krebs cycle-derived immunometabolite, is synthesized by myeloid cells in response to danger signals to control inflammasome activation, type I interferon (IFN) responses, and oxidative stress. As these pathways are dysregulated in systemic lupus erythematosus (SLE), we investigated the role of an itaconic acid derivative in the treatment of established murine lupus. METHODS: Female (NZW × NZB)F1 lupus-prone mice were administered 4-octyl itaconate (4-OI) or vehicle starting after clinical onset of disease (30 weeks of age) for 4 weeks (n = 10 mice /group). At 34 weeks of age (peak disease activity), animals were euthanized, organs and serum were collected, and clinical, metabolic, and immunologic parameters were evaluated. RESULTS: Proteinuria, kidney immune complex deposition, renal scores of severity and inflammation, and anti-RNP autoantibodies were significantly reduced in the 4-OI treatment group compared to the vehicle group. Splenomegaly decreased in the 4-OI group compared to vehicle, with decreases in activation markers in innate and adaptive immune cells, increases in CD8+ T cell numbers, and inhibition of JAK1 activation. Gene expression analysis in splenocytes showed significant decreases in type I IFN and proinflammatory cytokine genes and increased Treg cell-associated markers in the 4-OI group compared to the vehicle group. In human control and lupus myeloid cells, 4-OI in vitro treatment decreased proinflammatory responses and B cell responses. CONCLUSIONS: These results support targeting immunometabolism as a potentially viable approach in autoimmune disease treatment, with 4-OI displaying beneficial roles attenuating immune dysregulation and organ damage in lupus.

Changes in cardiorespiratory function and fatigue following 12 weeks of exercise training in women with systemic lupus erythematosus: a pilot study.

OBJECTIVE: In patients with systemic lupus erythematosus (SLE), fatigue is a debilitating symptom with poorly understood pathophysiology. Cardiorespiratory dysfunction has been hypothesised as a contributor to SLE-fatigue. The purpose of this exploratory study was to examine changes in cardiorespiratory function, following an exercise training programme in women with SLE, together with patient reported outcomes and other pathophysiological measures that may underlie SLE-fatigue. METHODS: Sixteen women with SLE and fatigue (Fatigue Severity Scale (FSS) ≥3) were enrolled in a supervised aerobic exercise training programme of vigorous intensity. The primary outcome was time to reach anaerobic threshold (AT-Time) during a cardiopulmonary exercise test (CPET). Secondary outcomes included changes in the 10-minute walk test (10MWT), FSS scores and the Patient Reported Outcomes Measurement Information System (PROMIS-57) survey. Mitochondrial function was assessed by the oxygen consumption rate (OCR)/extracellular acidification rate (ECAR) metabolic potential ratio. RESULTS: Following 12 weeks of exercise training, AT-Time increased by 93±82 (mean±SD) s (p<0.001), 10MWT increased by 84±66 m (p<0.001) and peak oxygen uptake (VO2) increased by 1.4±2.0 mL/kg/min (p=0.013). There were improvements in FSS score (-1.4±1.0, p<0.0001) and in most of the PROMIS-57 domains. The decrease in FSS scores correlated with an increase in the OCR/ECAR ratio (Pearson's correlation r=-0.59, p=0.03). A subset of subjects (9/15) had significant reduction in their Interferon Stimulated Genes (ISG) (p=0.007) accompanied by a significant increase in the OCR/ECAR ratio (p=0.013). CONCLUSIONS: Cardiorespiratory function was improved in concomitance with reductions in fatigue following a 12-week aerobic exercise programme. The reduction in fatigue scores correlated with improvements in mitochondrial function.