Lennart Truedsson

A regulatory polymorphism in PDCD1 is associated with susceptibility to systemic lupus erythematosus in humans

Systemic lupus erythematosus (SLE, OMIM 152700) is a complex autoimmune disease that affects 0.05% of the Western population, predominantly women. A number of susceptibility loci for SLE have been suggested in different populations, but the nature of the susceptibility genes and mutations is yet to be identified. We previously reported a susceptibility locus (SLEB2) for Nordic multi-case families. Within this locus, the programmed cell death 1 gene (PDCD1, also called PD-1) was considered the strongest candidate for association with the disease. Here, we analyzed 2,510 individuals, including members of five independent sets of families as well as unrelated individuals affected with SLE, for single-nucleotide polymorphisms (SNPs) that we identified in PDCD1. We show that one intronic SNP in PDCD1 is associated with development of SLE in Europeans (found in 12% of affected individuals versus 5% of controls; P = 0.00001, r.r. (relative risk) = 2.6) and Mexicans (found in 7% of affected individuals versus 2% of controls; P = 0.0009, r.r. = 3.5). The associated allele of this SNP alters a binding site for the runt-related transcription factor 1 (RUNX1, also called AML1) located in an intronic enhancer, suggesting a mechanism through which it can contribute to the development of SLE in humans.

Functional variants in the B-cell gene BANK1 are associated with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease characterized by production of autoantibodies and complex genetic inheritance. In a genome-wide scan using 85,042 SNPs, we identified an association between SLE and a nonsynonymous substitution (rs10516487, R61H) in the B-cell scaffold protein with ankyrin repeats gene, BANK1. We replicated the association in four independent case-control sets (combined P = 3.7 × 10−10; OR = 1.38). We analyzed BANK1 cDNA and found two isoforms, one full-length and the other alternatively spliced and lacking exon 2 (Δ2), encoding a protein without a putative IP3R-binding domain. The transcripts were differentially expressed depending on a branch point–site SNP, rs17266594, in strong linkage disequilibrium (LD) with rs10516487. A third associated variant was found in the ankyrin domain (rs3733197, A383T). Our findings implicate BANK1 as a susceptibility gene for SLE, with variants affecting regulatory sites and key functional domains. The disease-associated variants could contribute to sustained B cell–receptor signaling and B-cell hyperactivity characteristic of this disease.

Activation of type I interferon system in systemic lupus erythematosus correlates with disease activity but not with antiretroviral antibodies

The objective was to investigate the relation between serum levels of interferon-α (IFN-α), the activity of an endogenous IFN-a inducing factor (SLE-IIF), clinical and immunological disease activity as well as serum levels of antiretroviral antibodies in SLE. Serum levels of IFN-α were measured in serial sera from 30 patients sampled at different stages of disease activity (SLEDAI score). The SLE-IIF activity was measured by its ability to induce IFN-α production in cultures of normal peripheral blood mononuclear cells. Both serum IFN-α and SLE-IIF increased markedly at flare in serially followed patients. The SLEDAI score, levels of anti-dsDNA antibodies and IL-10 correlated positively, and complement components Clq, C3 and leukocytes correlated inversely with serum concentrations of IFN-α. The extent of multiple organ involvement correlated with serum IFN-α. No relation between concentrations of retroviral peptide binding antibodies and IFN-α or SLE-IIF activity was found. The close relationship between disease activity in SLE patients and IFN-α serum levels suggests that activation of the type I IFN system might be of importance in the disease process.

Neutrophil Extracellular Traps That Are Not Degraded in Systemic Lupus Erythematosus Activate Complement Exacerbating the Disease

Ongoing inflammation including activation of the complement system is a hallmark of systemic lupus erythematosus (SLE). Antimicrobial neutrophil extracellular traps (NETs) are composed of secreted chromatin that may act as a source of autoantigens typical for SLE. In this study, we investigated how complement interacts with NETs and how NET degradation is affected by complement in SLE patients. We found that sera from a subset of patients with active SLE had a reduced ability to degrade in vitro-generated NETs, which was mostly restored when these patients were in remission. Patients that failed to degrade NETs had a more active disease and they also displayed lower levels of complement proteins C4 and C3 in blood. We discovered that NETs activated complement in vitro and that deposited C1q inhibited NET degradation including a direct inhibition of DNase-I by C1q. Complement deposition on NETs may facilitate autoantibody production, and indeed, Abs against NETs and NET epitopes were more pronounced in patients with impaired ability to degrade NETs. NET-bound autoantibodies inhibited degradation but also further increased C1q deposition, potentially exacerbating the disease. Thus, NETs are a potent complement activator, and this interaction may play an important role in SLE. Targeting complement with inhibitors or by removing complement activators such as NETs could be beneficial for patients with SLE.

Complement deficiencies and systemic lupus erythematosus.

The complement system involves both the innate and the adaptive immune systems and has important roles in the pathogenesis of SLE. Complement deficiencies within the classical pathway (C1q, C4 and C2) of activation predispose for development of the autoimmune disease SLE. The association between complement deficiencies and SLE could be explained by several mechanisms, including impaired clearance of immune complexes and impaired handling of apoptotic cells, aberrant tolerance induction or changes in cytokine regulation. Also during SLE disease flares, the complement system is activated giving rise to partial deficiency or dysfunction due to consumption. On the other hand, complement also takes part in the inflammatory reaction in the disease that gives rise to the tissue and organ damage. In this review various aspects of the relation between complement and SLE are discussed.

A risk haplotype of STAT4 for systemic lupus erythematosus is over-expressed, correlates with anti-dsDNA and shows additive effects with two risk alleles of IRF5

Systemic lupus erythematosus (SLE) is the prototype autoimmune disease where genes regulated by type I interferon (IFN) are over-expressed and contribute to the disease pathogenesis. Because signal transducer and activator of transcription 4 (STAT4) plays a key role in the type I IFN receptor signaling, we performed a candidate gene study of a comprehensive set of single nucleotide polymorphism (SNPs) in STAT4 in Swedish patients with SLE. We found that 10 out of 53 analyzed SNPs in STAT4 were associated with SLE, with the strongest signal of association (P = 7.1 × 10−8) for two perfectly linked SNPs rs10181656 and rs7582694. The risk alleles of these 10 SNPs form a common risk haplotype for SLE (P = 1.7 × 10−5). According to conditional logistic regression analysis the SNP rs10181656 or rs7582694 accounts for all of the observed association signal. By quantitative analysis of the allelic expression of STAT4 we found that the risk allele of STAT4 was over-expressed in primary human cells of mesenchymal origin, but not in B-cells, and that the risk allele of STAT4 was over-expressed (P = 8.4 × 10−5) in cells carrying the risk haplotype for SLE compared with cells with a non-risk haplotype. The risk allele of the SNP rs7582694 in STAT4 correlated to production of anti-dsDNA (double-stranded DNA) antibodies and displayed a multiplicatively increased, 1.82-fold risk of SLE with two independent risk alleles of the IRF5 (interferon regulatory factor 5) gene.

Cardiovascular Disease in Systemic Lupus Erythematosus A Study of 75 Patients from a Defined Population

All patients with systemic lupus erythematosus in a prospective, epidemiologically based study within a defined area in southern Sweden were invited to participate in an investigation of cardiac function. From 1981 to 1988, 101 patients were included in the study, and 75 of them were investigated according to a fixed protocol by echocardiography, Doppler cardiography, electrocardiography (ECG) at rest and at exercise, and myocardial scintigraphy (in patients whose ECG became abnormal during exercise). IgG anticardiolipin antibodies (IgG aCL) were determined by ELISA. Twenty of the 75 patients (27%) had valvular disease and 12 of these (60%) had increased concentrations of IgG aCL, compared with 12 of 55 (22%) without valvular disease (p less than 0.01). Pericardial effusion was detected in 14 patients (19%) during the study period. Mild pulmonary hypertension was found in 11 patients (16%), who also had increased frequency of IgG aCL. Myocardial infarction had occurred in 7 patients, 3 of whom were women less than 40 years of age. Echocardiography revealed regional hypokinesis or akinesis in 5 of the patients with myocardial infarction. Exercise testing revealed low work capacity in 13 of 54 patients (24%), the limiting symptoms being mainly exhaustion or musculoskeletal pain. An abnormal resting ECG was found in 9 of the patients participating in the exercise test. During exercise, abnormal ST-depression was observed in 8 patients, 2 of whom developed angina. Myocardial scintigraphy was performed in 6 of these patients, revealing reversible uptake defects in all. Prolonged glucocorticoid treatment was associated with valvular abnormalities as well as myocardial infarction. Valvular abnormalities and IgG aCL appeared to be risk factors for cerebral infarction.

Hereditary C2 Deficiency in Sweden: Frequent Occurrence of Invasive Infection, Atherosclerosis, and Rheumatic Disease.

Abstract: Although frequently asymptomatic, homozygous C2 deficiency (C2D) is known to be associated with severe infections and rheumatic disease. We describe the clinical findings in 40 persons with C2D from 33 families identified in Sweden over 25 years. Medical records covering 96% of the accumulated person-years were reviewed, giving a mean observation time of 39 years (range, 1-77 yr). Severe infection was the predominant clinical manifestation in the cohort: 23 patients had a past history of invasive infections, mainly septicemia or meningitis caused by Streptococcus pneumoniae, and 12 patients had repeated infections of this kind. Nineteen patients had at least 1 episode of pneumonia, and recurrent pneumonia was documented in 10 patients. Repeated infections occurred mainly during infancy and childhood. Systemic lupus erythematosus was found in 10 patients. Another 7 patients had undifferentiated connective tissue disease (n = 4) or vasculitis (n = 3). We found no correlation between susceptibility to invasive infection and rheumatologic disease. Cardiovascular disease occurred at a high rate, with a total of 10 acute myocardial infarctions and 5 cerebrovascular episodes in 6 patients. Causes of death among the C2D patients were infection (n = 5), acute myocardial infarction (n = 3), and cancer (n = 1). We suggest that severe infection may be the principal clinical manifestation of C2D. We also provide novel evidence for a possible role of C2D in the development of atherosclerosis consistent with findings in mannan-binding deficiency and experimental C3 deficiency. In addition, we confirm the well-known association between C2D and systemic lupus erythematosus. Abbreviations: ACR = American College of Rheumatology, AMI = acute myocardial infarction, ANA = antinuclear antibodies, C2D = homozygous C2 deficiency, MASP = MBL-associated serine protease, MBL = mannan-binding lectin, MHC = major histocompatibility complex, PCR = polymerase chain reaction, SLE = systemic lupus erythematosus.

Platelet transcriptional profile and protein expression in patients with systemic lupus erythematosus: up-regulation of the type I interferon system is strongly associated with vascular disease

Patients with systemic lupus erythematosus (SLE) have a markedly increased risk to develop cardiovascular disease, and traditional cardiovascular risk factors fail to account for this increased risk. We used microarray to probe the platelet transcriptome in patients with SLE and healthy controls, and the gene and protein expression of a subset of differentially expressed genes was further investigated and correlated to platelet activation status. Real-time PCR was used to confirm a type I interferon (IFN) gene signature in patients with SLE, and the IFN-regulated proteins PRKRA, IFITM1 and CD69 (P < .0001) were found to be up-regulated in platelets from SLE patients compared with healthy volunteers. Notably, patients with a history of vascular disease had increased expression of type I IFN-regulated proteins as well as more activated platelets compared with patients without vascular disease. We suggest that interferogenic immune complexes stimulate production of IFNα that up-regulates the megakaryocytic type I IFN-regulated genes and proteins. This could affect platelet activation and contribute to development of vascular disease in SLE. In addition, platelets with type I IFN signature could be a novel marker for vascular disease in SLE.

C1q Inhibits Immune Complex-Induced Interferon-alpha Production in Plasmacytoid Dendritic Cells A Novel Link Between C1q Deficiency and Systemic Lupus Erythematosus Pathogenesis

OBJECTIVE C1q deficiency is the strongest risk factor known for the development of systemic lupus erythematosus (SLE), since almost all humans with a genetic deficiency of C1q develop this disease. Low C1q serum concentration is also a typical finding in SLE during flares, emphasizing the involvement of C1q in SLE pathogenesis. Recent studies have revealed that C1q has a regulatory effect on Toll-like receptor-induced cytokine production. Therefore, we undertook this study to investigate whether C1q could regulate production of interferon-alpha (IFNalpha). METHODS Peripheral blood mononuclear cells (PBMCs) and plasmacytoid dendritic cells (PDCs) were stimulated with 3 known interferogenic stimuli and cultured with physiologic concentrations of C1q. IFNalpha production was determined by an immunoassay. RESULTS C1q significantly inhibited PBMC IFNalpha production induced by RNA-containing immune complexes (ICs), herpes simplex virus (HSV), and CpG DNA. C1q also inhibited PDC IFNalpha production induced by ICs and CpG DNA but increased PDC IFNalpha production induced by HSV. The regulatory role of C1q was not specific for IFNalpha but was also seen for interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha. We demonstrated binding of C1q to PDCs both by surface plasmon resonance interaction analysis and by flow cytometry, and we also demonstrated intracellular detection of 2 C1q binding proteins. CONCLUSION Our findings contribute to the understanding of why C1q deficiency is such a strong risk factor for SLE and suggest an explanation for the up-regulation of the type I IFN system seen in SLE patients.