Formation of robust bound states of interacting microwave photons.

Systems of correlated particles appear in many fields of modern science and represent some of the most intractable computational problems in nature. The computational challenge in these systems arises when interactions become comparable to other energy scales, which makes the state of each particle depend on all other particles1. The lack of general solutions for the three-body problem and acceptable theory for strongly correlated electrons shows that our understanding of correlated systems fades when the particle number or the interaction strength increases. One of the hallmarks of interacting systems is the formation of multiparticle bound states2-9. Here we develop a high-fidelity parameterizable fSim gate and implement the periodic quantum circuit of the spin-½ XXZ model in a ring of 24 superconducting qubits. We study the propagation of these excitations and observe their bound nature for up to five photons. We devise a phase-sensitive method for constructing the few-body spectrum of the bound states and extract their pseudo-charge by introducing a synthetic flux. By introducing interactions between the ring and additional qubits, we observe an unexpected resilience of the bound states to integrability breaking. This finding goes against the idea that bound states in non-integrable systems are unstable when their energies overlap with the continuum spectrum. Our work provides experimental evidence for bound states of interacting photons and discovers their stability beyond the integrability limit.

Accurately computing the electronic properties of a quantum ring.

A promising approach to study condensed-matter systems is to simulate them on an engineered quantum platform1-4. However, the accuracy needed to outperform classical methods has not been achieved so far. Here, using 18 superconducting qubits, we provide an experimental blueprint for an accurate condensed-matter simulator and demonstrate how to investigate fundamental electronic properties. We benchmark the underlying method by reconstructing the single-particle band structure of a one-dimensional wire. We demonstrate nearly complete mitigation of decoherence and readout errors, and measure the energy eigenvalues of this wire with an error of approximately 0.01 rad, whereas typical energy scales are of the order of 1 rad. Insight into the fidelity of this algorithm is gained by highlighting the robust properties of a Fourier transform, including the ability to resolve eigenenergies with a statistical uncertainty of 10-4 rad. We also synthesize magnetic flux and disordered local potentials, which are two key tenets of a condensed-matter system. When sweeping the magnetic flux we observe avoided level crossings in the spectrum, providing a detailed fingerprint of the spatial distribution of local disorder. By combining these methods we reconstruct electronic properties of the eigenstates, observing persistent currents and a strong suppression of conductance with added disorder. Our work describes an accurate method for quantum simulation5,6 and paves the way to study new quantum materials with superconducting qubits.

Observation of Broadband Entanglement in Microwave Radiation from a Single Time-Varying Boundary Condition.

Entangled pairs of microwave photons are commonly produced in the narrow frequency band of a resonator, which represents a modified vacuum density of states. We generate and investigate the entanglement of a stream of photon pairs, generated in a semi-infinite broadband transmission line, terminated by a superconducting quantum interference device (SQUID). A weak pump signal modulates the SQUID inductance, resulting in a single time-varying boundary condition, and we detect all four quadratures of the microwave radiation emitted at two different frequencies separated by 0.7 GHz. Power calibration is done in situ, and we find positive logarithmic negativity and two-mode squeezing below the vacuum in the observed radiation, indicating entanglement.

Role of Thermal Equilibrium Dynamics in Atomic Motion during Nonthermal Laser-Induced Melting.

This study shows that initial atomic velocities as given by thermodynamics play an important role in the dynamics of phase transitions. We tracked the atomic motion during nonthermal laser-induced melting of InSb at different initial temperatures. The ultrafast atomic motion following bond breaking can in general be governed by two mechanisms: the random velocity of each atom at the time of bond breaking (inertial model), and the forces acting on the atoms after bond breaking. The melting dynamics was found to follow the inertial model over a wide temperature range.

Good survival rates in systemic lupus erythematosus in southern Sweden, while the mortality rate remains increased compared with the population.

OBJECTIVE: To ascertain the mortality rate and causes of death in patients with systemic lupus erythematosus (SLE) within a defined region in southern Sweden during the time period 1981-2014 and determine whether these have changed over time. METHODS: In 1981, a prospective observation study of patients with SLE was initiated in southern Sweden. All incident SLE patients within a defined geographic area were identified using previously validated methods including diagnosis and immunology registers. Patients with a confirmed SLE diagnosis were then followed prospectively at the Department of Rheumatology in Lund. Clinical data was collected at regular visits. Patients were recruited from 1981 to 2006 and followed until 2014. The patient cohort was split into two groups based on the year of diagnosis to determine secular trends. Causes of death were retrieved from medical records and from the cause of death registry at The National Board of Health and Welfare in Sweden. RESULTS: In all, 175 patients were diagnosed with SLE during the study period. A total of 60 deaths occurred during a total of 3053 years of follow-up. In the first half of the study inclusion period 46 patients died, compared with 14 in the latter. The majority of patients (51.7%) died of cardiovascular disease. Infections caused 15% of the deaths and malignancy was the cause of death in 13.3% of patients. SLE was the main cause of death for 6.7% of the patients and a contributing factor for half of the patients. Standardized mortality ratio was increased in patients by a factor of 2.5 compared with the general population. Deaths occurred at an even rate throughout the whole observation period. No significant difference in standardized mortality ratio was observed between genders but was increased in older female patients. Furthermore, secular mortality trends were not identified. CONCLUSIONS: In this long-term epidemiologic follow-up study of incident SLE, we report a substantially raised mortality rate amongst SLE patients compared with the general population. The mortality rates have not changed significantly during the observation period that spanned three decades. The main cause of death was cardiovascular disease and this finding was consistent over time.

White matter lesions and brain atrophy in systemic lupus erythematosus patients: correlation to cognitive dysfunction in a cohort of systemic lupus erythematosus patients using different definition models for neuropsychiatric systemic lupus erythematosus.

Aim The aim of this study was to evaluate the extent of white matter lesions, atrophy of the hippocampus and corpus callosum, and their correlation with cognitive dysfunction (CD), in patients diagnosed with systemic lupus erythematosus (SLE). Methods Seventy SLE patients and 25 healthy individuals (HIs) were included in the study. To evaluate the different SLE and neuropsychiatric SLE (NPSLE) definition schemes, patients were grouped both according to the American College of Rheumatology (ACR) definition, as well as the more stringent ACR-Systemic Lupus International Collaborating Clinics definition. Patients and HIs underwent a 3 Tesla brain MRI and a standardized neuropsychological test. MRI data were evaluated for number and volume of white matter lesions and atrophy of the hippocampus and corpus callosum. Differences between groups and subgroups were evaluated for significance. Number and volume of white matter lesions and atrophy of the hippocampus and corpus callosum were correlated to cognitive dysfunction. Results The total volume of white matter lesions was significantly larger in SLE patients compared to HIs ( p = 0.004). However, no significant differences were seen between the different SLE subgroups. Atrophy of the bilateral hippocampus was significantly more pronounced in patients with NPSLE compared to those with non-NPSLE (right: p = 0.010; left p = 0.023). Significant negative correlations between cognitive test scores on verbal memory and number and volume of white matter lesions were present. Conclusion SLE patients have a significantly larger volume of white matter lesions on MRI compared to HIs and the degree of white matter lesion volume correlates to cognitive dysfunction, specifically to verbal memory. No significant differences in the number or volume of white matter lesions were identified between subgroups of SLE patients regardless of the definition model used.

Tumour necrosis factor-α/etanercept complexes in serum predict long-term efficacy of etanercept treatment in seronegative rheumatoid arthritis.

OBJECTIVE: To study whether serum levels of tumour necrosis factor-α (TNF-α), free or bound to etanercept, in biological-naïve adults with rheumatoid arthritis (RA) could predict the long-term efficacy of etanercept, measured as drug survival. METHOD: We identified 145 biological-naïve patients with RA starting treatment with etanercept at the Department of Rheumatology, Skåne University Hospital (1999-2008), of whom 16 had seronegative and 129 seropositive RA. TNF-α in serum was quantified using enzyme-linked immunosorbent assay in samples from the onset of treatment and at 6 week follow-up. Drug survival time was used to evaluate the long-term efficacy of etanercept. RESULTS: Levels of TNF-α were significantly increased at follow-up compared to at the start. At the 6 week follow-up, circulating TNF-α mainly comprised TNF-α in complex with etanercept. Longer drug survival time correlated with increased TNF-α at 6 week follow-up in the patients with seronegative RA, but not in the seropositive patients. CONCLUSION: We demonstrated that levels of circulating TNF-α increased in almost all individuals after initiation of treatment with etanercept and that this increase mainly comprised TNF-α in complex with etanercept. More importantly, this increase may predict drug survival in adults with seronegative, but not seropositive, RA and suggests that measuring TNF-α/etanercept complexes in serum may be relevant in patients with seronegative RA.

Systemic lupus erythematosus: still a challenge for physicians.

Systemic lupus erythematosus (SLE) has a complex clinical picture, and a number of defects in the immune system have been described in patients with the disease. Most organs can be involved in SLE, and in addition to the typical major organ manifestations (e.g. from kidneys and the central nervous system), early cardiovascular disease is a major determinant of prognosis. Several important findings during the last decade have increased the understanding of the mechanisms behind the disease characteristics and the underlying autoimmune process. Amongst, these are defects in the handling of apoptotic cells, increased expression of type I interferon-regulated genes and activation of autoreactive B cells, with both the type I interferon system and the B lymphocyte stimulator (BLyS) having key roles. In addition, a large number of genes have been identified that contribute to these abnormalities. It has also become clear that certain SLE risk genes are associated with some organ manifestations, such as STAT4 with nephritis and IRF8 with myocardial infarction. Furthermore, environmental factors that can induce SLE or trigger a disease flare have been identified. As a consequence of this increased knowledge, new treatments for SLE have been developed. The most recently approved drug for SLE is belimumab, which blocks BLyS, and several new therapies and therapeutic strategies are in the pipeline for clinical application.

Deciphering systemic lupus erythematosus-associated serum biomarkers reflecting apoptosis and disease activity.

Systemic lupus erythematosus (SLE) is a severe chronic inflammatory autoimmune connective tissue disease. Despite major efforts, SLE remains a poorly understood disease with unpredictable course, unknown etiology and complex pathogenesis. Apoptosis combined with deficiency in clearing apoptotic cells is an important etiopathogenic event in SLE, which could contribute to the increased load of potential autoantigen(s); however, the lack of disease-specific protein signatures deciphering SLE and the underlying biological processes is striking and represents a key limitation. In this retrospective pilot study, we explored the immune system as a specific sensor for disease, in order to advance our understanding of SLE. To this end, we determined multiplexed serum protein expression profiles of crude SLE serum samples, using antibody microarrays. The aim was to identify differential immunoprofiles, or snapshots of the immune response modulated by the disease, reflecting apoptosis, a key process in the etiology of SLE and disease activity. The results showed that multiplexed panels of SLE-associated serum biomarkers could be decoded, in particular reflecting disease activity, but potentially the apoptosis process as well. While the former biomarkers could display a potential future use for prognosis, the latter biomarkers might help shed further light on the apoptosis process taking place in SLE.

Pro-inflammatory S100 proteins are associated with glomerulonephritis and anti-dsDNA antibodies in systemic lupus erythematosus.

Objectives Systemic lupus erythematosus (SLE) is associated with elevated levels of S100A8/A9, pro-inflammatory proteins mainly secreted by activated polymorphonuclear neutrophils (PMNs). The underlying mechanisms for increased S100A8/A9 levels and their relation to the clinical phenotype have not been carefully investigated. We assessed S100A8/A9 and S100A12 levels in SLE patient sera in relation to disease activity, clinical phenotype, presence of anti-dsDNA antibodies and ability to promote phagocytosis of necrotic cells (NCs) by PMNs. Methods Serum levels of S100A8/A9 and S100A12 were measured by ELISA in paired samples of 100 SLE patients at time points of higher and lower disease activity. Serum-mediated phagocytosis of NCs by PMNs was analysed by flow cytometry. Clinical data were recorded at time points of blood sampling. Results Serum levels of S100A8/A9 and S100A12 were increased in SLE patients with high disease activity compared to paired samples at low disease activity ( p = 0.01 and p = 0.008, respectively). Elevated levels of S100A8/A9 were particularly seen in patients with anti-dsDNA antibodies ( p = 0.01) and glomerulonephritis before treatment ( p = 0.02). Immunosuppressive therapy was associated with a reduction of S100A8/A9 serum levels ( p = 0.002). The ability of serum to support phagocytosis of NCs by PMNs was related to increased S100A8/A9 levels ( p = 0.01). Conclusions Elevated serum levels of S100A8/A9 may be used to monitor disease activity and response to treatment in SLE patients, especially in patients with glomerulonephritis. S100A12 may be a marker of disease activity in SLE. Increased S100A8/A9 levels may reflect immune-pathological processes involving phagocytosis of immune complexes by PMNs.

Treatment with belimumab in systemic lupus erythematosus does not impair antibody response to 13-valent pneumococcal conjugate vaccine.

Background/purpose The objective of this study was to explore the impact of systemic lupus erythematosus and belimumab given in addition to standard of care therapy on 13-valent conjugated pneumococcal vaccine (PCV13) response. Methods Forty-seven systemic lupus erythematosus patients and 21 healthy controls were immunized with a single dose of 13-valent conjugated pneumococcal vaccine. Forty systemic lupus erythematosus patients were treated with traditional disease-modifying anti rheumatic drugs, 11 of those received belimumab in addition, and 32 patients were treated with concomitant prednisolone. Quantification of serotype specific IgG levels to 12 pneumococcal capsular polysaccharides was performed in serum taken before and four to six weeks after vaccination using multiplex fluorescent microsphere immunoassay. IgG levels against serotypes 23F and 6B were also analyzed using standard enzyme-linked immunosorbent assays. Opsonophagocytic assay was performed on serotype 23F to evaluate the functionality of the antibodies. Pre- and post-vaccination log transformed antibody levels were compared to determine the impact of systemic lupus erythematosus diagnosis and different treatments on antibody response. Results Systemic lupus erythematosus patients as a group showed lower post-vaccination antibody levels and lower fold increase of antibody levels after vaccination compared to controls ( p = 0.02 and p = 0.009, respectively). Systemic lupus erythematosus patients treated with belimumab in addition to standard of care therapy or with only hydroxychloroquine did not differ compared to controls, whereas the other treatment groups had significantly lower fold increase of post-vaccination antibody levels. Higher age was associated with lower post-vaccination antibody levels among systemic lupus erythematosus patients. Conclusion Belimumab given in addition to traditional disease-modifying anti rheumatic drugs or prednisolone did not further impair antibody response to 13-valent conjugated pneumococcal vaccine.

Differences in body structure and function between patients with systemic lupus erythematosus and healthy individuals, with particular reference to joint hypermobility.

OBJECTIVES: To explore differences in body structure and function in systemic lupus erythematosus (SLE) patients and controls, with particular reference to joint hypermobility, and to evaluate the usefulness of the Brighton criteria for diagnosing joint hypermobility syndrome (JHS) in SLE. METHOD: Female SLE patients were, according to age group, consecutively invited to participate in the study. Controls were healthy females matched for age. All individuals were examined by a physician according to the Brighton criteria, and by an occupational therapist and a physiotherapist to obtain the Beighton scores, overall joint mobility, and manifestations in body structure and function. RESULTS: Sixteen (23%) SLE patients and 19 (27%) controls had a Beighton score ≥ 4 (non-significant, ns), and 39 (55%) individuals in the SLE group and 22 (31%) in the control group satisfied the Brighton criteria for JHS (p < 0.01). Many individuals in both groups exceeded the normative values for joint mobility in joints other than those included in the Beighton score. Stratifying for a Beighton score ≥ 4 vs. < 4, there were no significant differences in body structure or body function constituting JHS either in the SLE patients or in the controls. CONCLUSIONS: Although the presence of joint hypermobility in SLE patients was frequent, we could not verify that this caused excess manifestations in addition to the SLE symptoms.

Variations in the epidemiology of systemic lupus erythematosus in southern Sweden.

OBJECTIVE: The epidemiology of systemic lupus erythematosus (SLE) within a defined region in southern Sweden was studied during the time period 1981-2006. Furthermore, whether the phenotypic expression of SLE changed during the study period was investigated. METHODS: Patients with suspected SLE were retrieved from diagnosis registries, hospital records and central laboratory databases. All new cases of SLE in this region were identified using validated retrieval methods and observed prospectively in a structured follow-up program. SLE disease manifestations, including classification criteria, were followed over time. RESULTS: A total of 174 cases were diagnosed with SLE during 1981-2006. In the first period of the study, from 1981 to 1993, the incidence of SLE was 5.0/100,000 inhabitants and in the second period of the study, 1994-2006, the annual incidence decreased to 2.8/100,000. During the first period the highest incidence was among females between the ages of 45 and 54 years; 15.1/100,000 inhabitants, which was reduced in the second period to 3.8/100,000. During the second period the highest age and sex specific incidence was among women between 25 and 34 years (6.6/100,000 inhabitants). The point prevalence of SLE on 31 December 1993 was 55/100,000 inhabitants compared with 31 December 2006, when it was 65/100,000 inhabitants. The phenotype of the disease did not vary significantly during the study period. CONCLUSION: The incidence rate of SLE in younger females remained stable from 1981 to 2006. However, in middle-aged women the incidence was substantially reduced in the latter half of the study period.

Total cost and cost predictors in systemic lupus erythematosus - 8-years follow-up of a Swedish inception cohort.

OBJECTIVE: To study the annual direct and indirect costs in systemic lupus erythematosus (SLE) and how age, disease manifestations, disease activity, and organ damage influence total costs and predicted costs for SLE. METHODS: Clinical data on all patients with a diagnosis of SLE living in a defined area in southern Sweden during eight years were linked to health authority registries and the social insurance system which contain data on cost. Cost data on four matched population controls for each patient were also extracted. The controls were matched for age, sex, and area of residence. RESULTS: Data from 127 patients with SLE and 508 population controls were extracted. The mean annual total cost for SLE patients was SEK 180,520 ($30,093); the highest costs were found in the subgroup with nephritis SEK 229,423 ($38,246). The total costs for the patient group were significantly higher (p < 0.05) compared to the population controls of SEK 59,985 ($10,000). Of the total costs, 72% were due to indirect costs, 3% to SLE-specific pharmaceuticals, and the remaining 25% were in- and outpatient related costs. During the study period, inpatient days decreased by 60%, while outpatient contacts increased by 25%. Age (inverse relation), increasing disease activity, and acquired organ damage were significant predictors of total costs (all p < 0.05). CONCLUSION: The total annual costs for unselected SLE patients were found to be three times those for matched population controls. Important predictors of total costs were found.

Hand function and performance of daily activities in systemic lupus erythematosus: a clinical study.

This clinical study was performed to investigate hand problems in individuals with systemic lupus erythematosus (SLE) in comparison with healthy controls, and to explore problems in the performance of daily activities related to these hand problems, in order to objectify findings from a previous mail survey. We also investigated whether a simple hand test could detect hand problems in SLE. All individuals, 71 with SLE and 71 healthy controls, were examined for manifestations in body structures and body functions of the hands with a study-specific protocol. The simple hand test was performed by all the individuals and the arthritis impact measurement scale (AIMS 2) questionnaire was completed by the SLE individuals. In the SLE group, 58% had some kind of difficulty in the simple hand test, compared with 8% in the control group. Fifty percent of the SLE individuals experienced problems in performing daily activities due to hand deficits. Pain in the hands, reduced strength and dexterity, Raynaud's phenomenon and trigger finger were the most prominent body functions affecting the performance of daily activities. Deficits in hand function are common in SLE and affect the performance of daily activities. The simple hand test may be a useful tool in detecting hand problems.

A follow-up meeting post death is appreciated by family members of deceased patients.

BACKGROUND: A practice with a follow-up meeting post death (FUMPD) with physician and staff for family members of patients who died in the intensive care unit (ICU) was started as a quality project to improve the support of families in post-ICU bereavement. A quality improvement control was conducted after 4 years. METHOD: The quality improvement control was made retrospectively as an anonymous non-coded questionnaire. Part A related to the FUMPD. Part B inquired if we could contact the family member again for a research project to evaluate family support post-ICU bereavement. The questionnaires were sent to 84 family members of 56 deceased patients. RESULTS: Part A: 46 out of 84 family members answered and had attended a FUMPD. Ninety-one percent of the family members thought that we should continue to offer FUMPD. Seventy-eight percent were satisfied with their meeting. Eighty percent felt that they understood the cause of death. The majority wanted the meeting to take place within 6 weeks of death. Ninety-one percent rated the physician as important to be present at the meeting. The social worker was rated more important to attend the meeting than the assistant nurse. Ninety-one percent wanted to discuss the cause of death.Part B: 54 out of 84 family members answered. Twenty out of 54 did not want us to contact them again. CONCLUSION: A routine with a Follow-Up Meeting Post Death with the ICU team for the families of the patients who die in the ICU is appreciated. The presence of the physician is important.

Dynamics of magnetization at infinite temperature in a Heisenberg spin chain.

Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain's center, [Formula: see text]. The first two moments of [Formula: see text] show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.

Stable quantum-correlated many-body states through engineered dissipation.

Engineered dissipative reservoirs have the potential to steer many-body quantum systems toward correlated steady states useful for quantum simulation of high-temperature superconductivity or quantum magnetism. Using up to 49 superconducting qubits, we prepared low-energy states of the transverse-field Ising model through coupling to dissipative auxiliary qubits. In one dimension, we observed long-range quantum correlations and a ground-state fidelity of 0.86 for 18 qubits at the critical point. In two dimensions, we found mutual information that extends beyond nearest neighbors. Lastly, by coupling the system to auxiliaries emulating reservoirs with different chemical potentials, we explored transport in the quantum Heisenberg model. Our results establish engineered dissipation as a scalable alternative to unitary evolution for preparing entangled many-body states on noisy quantum processors.

Contribution of IKBKE and IFIH1 gene variants to SLE susceptibility.

The type I interferon system genes IKBKE and IFIH1 are associated with the risk of systemic lupus erythematosus (SLE). To identify the sequence variants that are able to account for the disease association, we resequenced the genes IKBKE and IFIH1. Eighty-six single-nucleotide variants (SNVs) with potentially functional effect or differences in allele frequencies between patients and controls determined by sequencing were further genotyped in 1140 SLE patients and 2060 controls. In addition, 108 imputed sequence variants in IKBKE and IFIH1 were included in the association analysis. Ten IKBKE SNVs and three IFIH1 SNVs were associated with SLE. The SNVs rs1539241 and rs12142086 tagged two independent association signals in IKBKE, and the haplotype carrying their risk alleles showed an odds ratio of 1.68 (P-value=1.0 × 10(-5)). The risk allele of rs12142086 affects the binding of splicing factor 1 in vitro and could thus influence its transcriptional regulatory function. Two independent association signals were also detected in IFIH1, which were tagged by a low-frequency SNV rs78456138 and a missense SNV rs3747517. Their joint effect is protective against SLE (odds ratio=0.56; P-value=6.6 × 10(-3)). In conclusion, we have identified new SLE-associated sequence variants in IKBKE and IFIH1, and proposed functional hypotheses for the association signals.

Increased serum type I interferon activity in early systemic sclerosis patients is associated with antibodies against Sjögren's syndrome antigens and nuclear ribonucleoprotein antigens.

OBJECTIVE: To study serum type I interferon (IFN) activity in patients with early systemic sclerosis (SSc). METHOD: Serum type I IFN activity was measured in 33 consecutive patients with SSc and a disease duration of < 2 years and in 13 healthy individuals by calculating a type I IFN score according to the induction of six IFN-α regulated genes in a reporter cell line. RESULTS: Twenty-seven per cent of the SSc patients had an increased type I IFN score compared to none of the healthy individuals (p < 0.05). The clinical SSc phenotype associated with high serum type I IFN activity did not differ from patients with low serum type I IFN activity regarding the presence of skin or lung fibrosis, pulmonary hypertension, or digital complications. Patients with high serum type I IFN activity were younger (p < 0.01) and had a lower frequency of cardiac involvement (p = 0.053), lower leucocyte count (p < 0.001), higher immunoglobulin (Ig)G levels (p < 0.05), and a higher amount of antibodies against extractable nuclear antigens (p < 0.01) than patients with low serum type I IFN activity. The presence of antibodies against topoisomerase I, Sjögren's syndrome antigen, and nuclear ribonucleoprotein antigens was associated with higher type I IFN activity (p < 0.05 for all comparisons). CONCLUSIONS: Our study indicates that increased serum type I IFN activity in early SSc patients is associated with an antibody and laboratory profile that may reflect a subclinical overlap of SSc with other type I IFN-driven connective tissue diseases (CTDs).