Mixed Connective Tissue Disease as Different Entity: Global Methylation Aspect.

Mixed connective tissue disease (MCTD) is a very rare disorder that belongs in the rare and clinically multifactorial groups of diseases. The pathogenesis of MCTD is still unclear. The best understood epigenetic alteration is DNA methylation whose role is to regulate gene expression. In the literature, there are ever-increasing assumptions that DNA methylation can be one of the possible reasons for the development of Autoimmune Connective Tissue Diseases (ACTDs) such as systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). The aim of this study was to define the global DNA methylation changes between MCTD and other ACTDs patients in whole blood samples. The study included 54 MCTD patients, 43 SSc patients, 45 SLE patients, and 43 healthy donors (HC). The global DNA methylation level was measured by ELISA. Although the global DNA methylation was not significantly different between MCTD and control, we observed that hypomethylation distinguishes the MCTD patients from the SSc and SLE patients. The present analysis revealed a statistically significant difference of global methylation between SLE and MCTD (p < 0.001), SLE and HC (p = 0.008), SSc and MCTD (p ≤ 0.001), and SSc and HC (p < 0.001), but neither between MCTD and HC (p = 0.09) nor SSc and SLE (p = 0.08). The highest % of global methylation (median, IQR) has been observed in the group of patients with SLE [0.73 (0.43, 1.22] and SSc [0,91 (0.59, 1.50)], whereas in the MCTD [0.29 (0.20, 0.54)], patients and healthy subjects [0.51 (0.24, 0.70)] were comparable. In addition, our study provided evidence of different levels of global DNA methylation between the SSc subtypes (p = 0.01). Our study showed that patients with limited SSc had a significantly higher global methylation level when compared to diffuse SSc. Our data has shown that the level of global DNA methylation may not be a good diagnostic marker to distinguish MCTD from other ACTDs. Our research provides the groundwork for a more detailed examination of the significance of global DNA methylation as a distinguishing factor in patients with MCTD compared to other ACTDs patients.

Predisposition of HLA-DRB1*04:01/*15 heterozygous genotypes to Japanese mixed connective tissue disease.

Mixed connective tissue disease (MCTD) is a rare systemic autoimmune disease characterized by the production of anti-U1 ribonucleoprotein antibodies and systemic symptoms similar to those of some other autoimmune diseases. HLA-DRB1 polymorphisms are important genetic risk factors for MCTD, but precise associations of DRB1 genotypes with MCTD have not been reported in Japanese people. Genotyping of HLA-DRB1 and -DQB1 was performed in Japanese MCTD patients (n = 116) and controls (n = 413). Associations of specific allele carriers and genotype frequencies with MCTD were analyzed.The following alleles were found to be associated with predisposition to MCTD: HLA-DRB1*04:01 (P = 8.66 × 10-6, Pc = 0.0003, odds ratio [OR] 7.96, 95% confidence interval [CI] 3.13‒20.24) and DRB1*09:01 (P = 0.0189, Pc = 0.5468, OR 1.73, 95% CI 1.12‒2.67). In contrast, the carrier frequency of the DRB1*13:02 allele (P = 0.0032, Pc = 0.0929, OR 0.28, 95% CI 0.11‒0.72) was lower in MCTD patients than in controls. The frequencies of heterozygosity for HLA-DRB1*04:01/*15 (P = 1.88 × 10-7, OR 81.54, 95% CI 4.74‒1402.63) and DRB1*09:01/*15 (P = 0.0061, OR 2.94, 95% CI 1.38‒6.25) were also higher in MCTD patients. Haplotype and logistic regression analyses suggested a predisposing role for HLA-DRB1*04:01, DQB1*03:03, and a protective role for DRB1*13:02. Increased frequencies of HLA-DRB1*04:01/*15 and DRB1*09:01/*15 heterozygous genotypes were found in Japanese MCTD patients.

Integrative Analysis Reveals a Molecular Stratification of Systemic Autoimmune Diseases.

OBJECTIVE: Clinical heterogeneity, a hallmark of systemic autoimmune diseases, impedes early diagnosis and effective treatment, issues that may be addressed if patients could be classified into groups defined by molecular pattern. This study was undertaken to identify molecular clusters for reclassifying systemic autoimmune diseases independently of clinical diagnosis. METHODS: Unsupervised clustering of integrated whole blood transcriptome and methylome cross-sectional data on 955 patients with 7 systemic autoimmune diseases and 267 healthy controls was undertaken. In addition, an inception cohort was prospectively followed up for 6 or 14 months to validate the results and analyze whether or not cluster assignment changed over time. RESULTS: Four clusters were identified and validated. Three were pathologic, representing "inflammatory," "lymphoid," and "interferon" patterns. Each included all diagnoses and was defined by genetic, clinical, serologic, and cellular features. A fourth cluster with no specific molecular pattern was associated with low disease activity and included healthy controls. A longitudinal and independent inception cohort showed a relapse-remission pattern, where patients remained in their pathologic cluster, moving only to the healthy one, thus showing that the molecular clusters remained stable over time and that single pathogenic molecular signatures characterized each individual patient. CONCLUSION: Patients with systemic autoimmune diseases can be jointly stratified into 3 stable disease clusters with specific molecular patterns differentiating different molecular disease mechanisms. These results have important implications for future clinical trials and the study of nonresponse to therapy, marking a paradigm shift in our view of systemic autoimmune diseases.

Association study between immune-related miRNAs and mixed connective tissue disease.

BACKGROUND: Mixed connective tissue disease (MCTD) is a rare condition that is distinguished by the presence of specific U1-RNP antibodies. Information about its etiopathology and diagnostics is still unclear. miRNAs such as miR-146, miR-155, and miR-143 emerged as key regulators of the immune system, known to be involved in the development of autoimmune diseases and cancers. We performed an association study between immune-related miRNAs and MCTD severity and susceptibility. METHODS: A total of 169 MCTD patients and 575 healthy subjects were recruited to the case-control study. The miRNA polymorphisms were genotyped using TaqMan SNP genotyping assay. TNF-α, IL-6, and IFN-γ levels in serum were determined using ELISA. qRT-PCR of TRAF6, IRAK1, and microRNAs was performed using Taqman miRNA assays and TaqMan Gene Expression Assays. RESULTS: miR-146a rs2910164 G allele and GG genotype as well as miR-143 rs713147 A allele were more frequent in healthy subjects than in MCTD patients. miR-146a rs2910164 CC genotype and miR-143 T-rs353299*T-rs353291*T-rs713147*G-rs353298 and C-rs353299*C-rs353291*T-rs713147*A-rs353298 haplotypes were associated with MCTD susceptibility. miR-146a rs2910164 C/T was associated with scleroderma and lymphadenopathy. miR-143 rs353299 C/T was associated with swollen fingers or hands, the presence of enlarged lymph nodes, and pericarditis/pleuritis. miR-143 rs353298 A/G was associated with the occurrence of pericarditis/pleuritis and scleroderma. miR-143 rs353291 T/C showed association with pericarditis/pleuritis. The serum TNF-α, IFN-γ, and IL-6 levels were significantly higher in MCTD patients compared to healthy subjects. miR-143 SNPs were associated with higher proinflammatory cytokine concentration in serum only in healthy controls. IRAK1 and TRAF6 expression were higher in the MCTD patients compared to controls. CONCLUSIONS: The results of our case-control study indicate the possible significance of miR-146a and miR-143/145 in the susceptibility and clinical picture of MCTD.

Variety of endosomal TLRs and Interferons (IFN-α, IFN-ß, IFN-γ) expression profiles in patients with SLE, SSc and MCTD.

We investigated Toll-like receptor (TLR)-3/-7/-8/-9 and interferon (IFN)-α/ß/γ mRNA expression in whole blood and serum IFN-α/ß/γ levels in patients with mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) and in healthy subjects to assess the association between the TLR-IFN expression and severity of and susceptibility to diseases, and identify potential biomarkers. Expression of the IFN-γ, TLR-3 and TLR-8 was detected only in SLE patients. TLR-7, IFN-α and IFN-ß expression was highest in SLE, while TLR-9 expression was highest in SSc patients. In SLE and MCTD patients a strong correlation was observed between TLR-7 and IFN-α expression and IFN-ß and IFN-α expression. In MCTD patients, negative correlation between IFN-α and TLR-9 and TLR-7 and TLR-9 was revealed. TLR-9 expression in anti-U1-70k-negative, anti-C negative and anti-SmB-negative MCTD patients was higher than in MCTD-positive patients. We observed negative correlations between serum IFN-α levels and TLR-7 expression and C3 and C4 levels in SLE patients. In SLE patients we observed that with increased IFN-γ, TLR-3 and TLR-8 expression increased the value of C3 and C4. Our results confirmed that the endosomal TLR-IFN pathway seems to be more important in SLE than in MCTD or SSc, and that IFN-α and IFN-ß may be possible biomarkers for SLE.

Is the T-G-CT-G SNRNP70 haplotype another proof that mixed connective tissue disease is distinct from systemic lupus erythematosus and systemic sclerosis? A novel gene variant in SNRNP70 gene.

OBJECTIVES: U1-70K, encoded by the SNRNP70 gene, is a key early immunogen in connective tissue disease. The aim of the study was the genetic analysis of the SNRNP70 gene in mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) patients. METHODS: SNRNP70 genetic variants were detected using 3730 DNA Analyzer. SNRNP70 rs560811128 G/A (c.476-252 G/A), rs78616533delCT (c.475+130_475+131delCT) and rs117167710 T/C (c.393+326 T/C) variants were genotyped using the technique of sequence-specific hybridisation probe binding assays. SNRNP70 393_47 G/A mutation was detected using TaqMan SNP genotyping assay. RESULTS: We found one novel c.393+47G>A and three, c.476-252 G/A, c.475+130_475+131delCT and c.393+326 T/C, previously recorded variants. The present study revealed that T-G-CT-G haplotype demonstrated significantly higher frequencies in MCTD patients than in SLE and SSc patients. In MCTD patients c.475+130_475+131delCT distribution of genotype was gender-dependent and showed association with thrombo-/leukocytopenia. Mutation at position c.476-252G>A was predicted to possibly have an impact on splicing of the SNRNP70 transcript and it was present only in one MCTD patient. CONCLUSIONS: Our results demonstrated that the T-G-CT-G SNRNP70 haplotype is another proof that MCTD may be distinct from SLE and SSc. The novel c.476-252G>A mutation in SNRNP70 gene created a new acceptor splice site and may potentially alert of splicing of the SNRNP70 transcript.

Epigenome-Wide Comparative Study Reveals Key Differences Between Mixed Connective Tissue Disease and Related Systemic Autoimmune Diseases.

Mixed Connective Tissue Disease (MCTD) is a rare complex systemic autoimmune disease (SAD) characterized by the presence of increased levels of anti-U1 ribonucleoprotein autoantibodies and signs and symptoms that resemble other SADs such as systemic sclerosis (SSc), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE). Due to its low prevalence, this disease has been very poorly studied at the molecular level. We performed for the first time an epigenome-wide association study interrogating DNA methylation data obtained with the Infinium MethylationEPIC array from whole blood samples in 31 patients diagnosed with MCTD and 255 healthy subjects. We observed a pervasive hypomethylation involving 170 genes enriched for immune-related function such as those involved in type I interferon signaling pathways or in negative regulation of viral genome replication. We mostly identified epigenetic signals at genes previously implicated in other SADs, for example MX1, PARP9, DDX60, or IFI44L, for which we also observed that MCTD patients exhibit higher DNA methylation variability compared with controls, suggesting that these sites might be involved in plastic immune responses that are relevant to the disease. Through methylation quantitative trait locus (meQTL) analysis we identified widespread local genetic effects influencing DNA methylation variability at MCTD-associated sites. Interestingly, for IRF7, IFI44 genes, and the HLA region we have evidence that they could be exerting a genetic risk on MCTD mediated through DNA methylation changes. Comparison of MCTD-associated epigenome with patients diagnosed with SLE, or Sjögren's Syndrome, reveals a common interferon-related epigenetic signature, however we find substantial epigenetic differences when compared with patients diagnosed with rheumatoid arthritis and systemic sclerosis. Furthermore, we show that MCTD-associated CpGs are potential epigenetic biomarkers with high diagnostic value. Our study serves to reveal new genes and pathways involved in MCTD, to illustrate the important role of epigenetic modifications in MCTD pathology, in mediating the interaction between different genetic and environmental MCTD risk factors, and as potential biomarkers of SADs.

A evolução do diagnóstico da doença mista do tecido conjuntivo / Evolution of the diagnosis of mixed connective tissue disease

A Doença Mista do Tecido Conjuntivo (DMTC) é uma doença autoimune crônica composta por um misto de quatro doenças: Lúpus Eritematoso Sistêmico, Esclerose Sistêmica, Dermatomiosite/Polimiosite e Artrite Reumatoide. Por se tratar de uma combinação de doenças autoimunes o diagnóstico é bastante complexo. Atualmente existem quatro combinações sugeridas por diferentes autores para a realização de um diagnóstico preciso, são eles: Kasukawa, Alarcón-Segovia e Villareal, Kahn e Appeboom e Sharp. Desde a sua descoberta em 1972 por Sharp, passaram-se 46 anos e desta forma o objetivo desta revisão foi verificar a evolução do diagnóstico da DMTC desde a sua descoberta até a atualidade. Para isso utilizou-se sites de busca PUBMED e SCIELO. Por se tratar de uma doença autoimune que leva ao desenvolvimento de um quadro inflamatório crônico utilizou-se a ferramenta STRING que permite a análise da interação de proteínas. Até a presente data, não existe um consenso de qual critério deve ser usado para o diagnóstico correto e eficiente desta doença. A baixa relação de interações observadas a partir da ferramenta STRING demonstra que ainda não existem dados suficientes na literatura para que a ligação entre proteínas marcadoras e a DTMC possa ser estabelecida. (AU)

Mixed connective tissue disease (MCTD) is a chronic autoimmune disorder consisting of a mixture of four diseases: systemic lupus erythematosus, systemic sclerosis, dermatomyositis/polymyositis, and rheumatoid arthritis. Because it is a combination of different autoimmune disorders its diagnosis is quite complex. Currently there are four combinations suggested by the following authors to establish an accurate diagnosis: Kasukawa, Alarcón-Segovia & Villareal, Kahn, and Appeboom & Sharp. It has been 46 years since Sharp reported the disease in 1972 and thus the purpose of this review was to investigate the evolution of the diagnosis of MCTD since then. PubMed and SciELO databases were used for this investigation. Because MCTD is an autoimmune disease that leads to the development of a chronic inflammatory condition, the STRING tool was used to allow the analysis of protein interaction. To date, there is no consensus as to what criterion should be used for a correct and efficient diagnosis of this disease. The low ratio of interactions observed from the STRING tool demonstrates that there is not yet enough data in the literature for establishing the binding between marker proteins and MCTD. (AU)

Association of HLA-DRB1 alleles with susceptibility to mixed connective tissue disease in Polish patients.

Mixed connective tissue disease (MCTD) is a systemic autoimmune disease, originally defined as a connective tissue inflammatory syndrome with overlapping features of systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), polymyositis/dermatomyositis (PM/DM) and systemic sclerosis (SSc), characterized by the presence of antibodies against components of the U1 small nuclear ribonucleoprotein (U1snRNP). The aim of the study was to assess the frequency of (high-resolution-typed) DRB1 alleles in a cohort of Polish patients with MCTD (n = 103). Identification of the variants potentially associated with risk and protection was carried out by comparison with the DKMS Polish Bone Marrow Donor Registry (41306 alleles). DRB1*15:01 (odds ratio (OR): 6.06; 95% confidence interval (CI) 4.55-8.06), DRB1*04 (OR: 3.69; 95% CI 2.69-5.01) and *09:01 (OR: 8.12; 95% CI 2.15-21.75) were identified as risk alleles for MCTD, while HLA-DRB1*07:01 allele was found to be protective (OR: 0.50; 95% CI 0.28-0.83). The carrier frequency of the DRB1*01 was higher in MCTD patients compared with controls, although the differences were not statistically significant. Our results confirm the modulating influence of HLA-DRB1 genotypes on development of connective tissue diseases such as MCTD.

Development of mixed connective tissue disease and Sjögren's syndrome in a patient with trisomy X.

Increased risk of developing systemic lupus erythematosus (SLE) has been reported in patients with Klinefelter syndrome. Here, we describe a 16-year-old Japanese patient with trisomy X (47,XXX) who developed mixed connective tissue disease (MCTD) and Sjögren's syndrome. She had polyarthritis, edematous fingers with Raynaud's phenomenon, sicca syndrome, interstitial lung disease, possible myositis, and was positive for anti-nuclear antibody, anti-nRNP antibody and rheumatoid factor. This is the first report in the literature of a case of MCTD with female polysomy X, which further supports the link between the presence of extra X chromosome(s) and the development of autoimmune diseases.

IL-10, IL-12B and IL-17 gene polymorphisms in patients with mixed connective tissue disease.

OBJECTIVES: Mixed connective tissue disease (MCTD) is a rare systemic autoimmune disease with a prevalence of about 10 cases/100,000. It seems that in the pathogenesis of MCTD no individual cytokines/cells, but rather an altered pattern of these markers altogether may contribute to the autoimmune processes and their balance determines disease activity. IL-10, IL-12 and IL-17F as inflammatory cytokines might be an important functional candidate genes for autoimmune diseases including MCTD. METHODS: The study group consisted of 66 patients with MCTD and of 106 (163 for IL-12B) healthy individuals. SNPs in the IL-10 (- 592C/A, - 1082G/A), IL-12B (+ 1188A/C) and IL-17F (His161Arg, Glu126Gly) genes were investigated by PCR-RFLP approach. RESULTS: The frequency of the IL-10-592A and -1082A allele was higher in MCTD patients than in control groups (both p = 0,0000). In addition the -1082G/A IL-10 gene polymorphism was associated with esophageal involvement and with anti-U1-A and -C antibodies. The IL-17 7488A/G variant showed correlation with presence of anti-SmB and anti-dsDNA antibodies, while the IL-17F 7383A/G variant was associated with Sjögren's syndrome and leuco-and thrombocytopenia. Moreover, the IL-12 SNP + 1188A/C showed correlation with sclerodactyly in MCTD patients. CONCLUSION: Present findings indicate that IL-10 gene variants may be considered as genetic risk factors for MCTD susceptibility.

The HLA profiles of mixed connective tissue disease differ distinctly from the profiles of clinically related connective tissue diseases.

OBJECTIVE: The Norwegian nationwide MCTD cohort was established to obtain unbiased data on key disease issues, and thereby reappraise the concept of MCTD. In the current study, the aims were to obtain detailed HLA profile data on the large Norwegian MCTD cohort and compare these with the HLA profiles of ethnically matched healthy controls and related CTD controls. METHODS: HLA profiles, determined by sequence-based typing of HLA-B* and DRB1*, were compared between four control groups of Norwegian ancestry, SLE (n = 96), SSc (n = 95), PM/DM (n = 84), healthy individuals (n = 282), the complete MCTD cohort (n = 155) and MCTD subsets defined by key clinical parameters. RESULTS: HLA-B*08 [odds ratio (OR) 2.05, P = 1.31 × 10(-4)) and DRB1*04:01 (OR 2.82, P = 3.64 × 10(-8)) were identified as risk alleles for MCTD, while DRB1*04:04, DRB1*13:01 and DRB1*13:02 were protective. Risk alleles for SLE and PM/DM were B*08 and DRB1*03:01. SSc risk was associated with DRB1*08:01. Analyses of MCTD subsets identified B*18 [OR 3.32 (95% CI 1.38, 8.01)] and DRB1*03:01 [OR 1.83 (95% CI 1.03, 3.25)] as independent risk factors for lung fibrosis. CONCLUSION: Novel HLA alleles associated with MCTD and disease subsets were identified and DRB1*04:01 was confirmed as a major risk allele. Altogether, the data reinforce the notion of MCTD as a disease entity distinct from SLE, SSc and PM/DM.

Elevated double negative T cells in pediatric autoimmunity.

PURPOSE: Autoimmune diseases are thought to be caused by a loss of self-tolerance of the immune system. One candidate marker of immune dysregulation in autoimmune disease is the presence of increased double negative T cells (DNTs) in the periphery. DNTs are characteristically elevated in autoimmune lymphoproliferative syndrome, a systemic autoimmune disease caused by defective lymphocyte apoptosis due to Fas pathway defects. DNTs have also been found in the peripheral blood of adult patients with systemic lupus erythematosus (SLE), where they may be pathogenic. DNTs in children with autoimmune disease have not been investigated. METHODS: We evaluated DNTs in pediatric patients with SLE, mixed connective tissue disease (MCTD), juvenile idiopathic arthritis (JIA), or elevated antinuclear antibody (ANA) but no systemic disease. DNTs (CD3(+)CD56(-)TCRαß(+)CD4(-)CD8(-)) from peripheral blood mononuclear cells were analyzed by flow cytometry from 54 pediatric patients including: 23 SLE, 15 JIA, 11 ANA and 5 MCTD compared to 28 healthy controls. RESULTS: Sixteen cases (29.6 %) had elevated DNTs (≥2.5 % of CD3(+)CD56(-)TCRαß(+) cells) compared to 1 (3.6 %) control. Medication usage including cytotoxic drugs and absolute lymphocyte count were not associated with DNT levels, and percentages of DNTs were stable over time. Analysis of multiple phenotypic and activation markers showed increased CD45RA expression on DNTs from patients with autoimmune disease compared to controls. CONCLUSION: DNTs are elevated in a subset of pediatric patients with autoimmune disease and additional investigations are required to determine their precise role in autoimmunity.

ANCA-associated vasculitis with dual ANCA positivity in coexistence with mixed connective tissue disease.

We here report a rare case of dual antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) in a 38-year-old Japanese woman previously diagnosed with mixed connective tissue disease. The patient was found to be positive for myeloperoxidase- and proteinase 3-ANCA, and was diagnosed with AAV following admission to hospital with fervescence, polyarthralgia, purpura, and asymmetric numbness of the extremities. Examination of her genetic background revealed that she carried HLA-DR9, which confers risk of both diseases in Japanese populations.

[Genetic and environmental contribution to rheumatoid arthritis: a family study]. / Studio di una famiglia con elevata concordanza per artrite reumatoide: ruolo dei fattori genetici, ambientali e costituzionali.

We report on the HLA typing of three brothers (A, B, C) with rheumatoid arthritis (RA) and their six sons. This family is interesting for the full concordance for RA between parents. The aim of this study was the discovery of genetic and/or enviromental cofactors determining this absolute concordance.

The molecular basis for the presence of two autoimmune diseases occurring simultaneously--preliminary observations based on computer analysis.

Specific Human Leukocyte Antigen Class II (HLA II) molecules associated with pemphigus vulgaris (PV), mucous membraine pemphigoid (MMP), and mixed connective tissue disease (MCTD) may react with multiple T cell epitopes within desmoglein 3 (Dsg 3), bullous pemphigoid antigen 2 (BPAG 2), and 70 kDa polypeptide small nuclear ribonucleoproteins (snRNP70) in autoantibody production. We report a group of patients with simultaneous occurrences of PV with MCTD, and MMP with MCTD. In one patient group, we performed serological studies to show presence of antibodies to Dsg 3, Dsg 1, and snRNP70 simultaneously. In the second group, we performed serological studies to show presence of antibodies to BPAG 1, BPAG 2, ß4 integrin, and snRNP70 simultaneously. In both groups, HLA II genes were analyzed and the observations were consistent with previously described associations with PV, MMP, and MCTD. It is possible that HLA-DQß1*0301 allele, present in 10 of 17 patients and DRß1*04 in some of the others, may have the ability to bind to several relevant T cell epitopes in the snRNP70 molecule. We have utilized a computer model to demonstrate that HLA II-restricted T cell epitopes present within the known autoantigens may be capable of eliciting an immune response. While other explanations and mechanisms exist, the authors suggest that epitope spreading may be one possible mechanism, amongst others, that may result in the simultaneous presence of two separate pathogenic autoantibodies.

Epitope mapping of the U1 small nuclear ribonucleoprotein particle in patients with systemic lupus erythematosus and mixed connective tissue disease.

Systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) are autoimmune illnesses characterized by the presence of high titers of autoantibodies directed against a wide range of 'self ' antigens. Proteins of the U1 small nuclear ribonucleoprotein particle (U1 snRNP) are among the most immunogenic molecules in patients with SLE and MCTD. The recent release of a crystallized U1 snRNP provides a unique opportunity to evaluate the effects of tertiary and quaternary structures on autoantigenicity within the U1 snRNP. In the present study, an epitope map was created using the U1 snRNP crystal structure. A total of 15 peptides were tested in a cohort of 68 patients with SLE, 29 with MCTD and 26 healthy individuals and mapped onto the U1 snRNP structure. Antigenic sites were detected in a variety of structures and appear to include RNA binding domains, but mostly exclude regions necessary for protein-protein interactions. These data suggest that while some autoantibodies may target U1 snRNP proteins as monomers or apoptosis-induced, protease-digested fragments, others may recognize epitopes on assembled protein subcomplexes of the U1 snRNP. Although nearly all of the peptides are strong predictors of autoimmune illness, none were successful at distinguishing between SLE and MCTD. The antigenicity of some peptides significantly correlated with several clinical symptoms. This investigation implicitly highlights the complexities of autoimmune epitopes, and autoimmune illnesses in general, and demonstrates the variability of antigens in patient populations, all of which contribute to difficult clinical diagnoses.

CD4+ T cells target epitopes residing within the RNA-binding domain of the U1-70-kDa small nuclear ribonucleoprotein autoantigen and have restricted TCR diversity in an HLA-DR4-transgenic murine model of mixed connective tissue disease.

Mixed connective tissue disease (MCTD) is a systemic autoimmune disease with significant morbidity and premature mortality of unknown pathogenesis. In the present study, we characterized U1-70-kDa small nuclear ribonucleoprotein (70-kDa) autoantigen-specific T cells in a new murine model of MCTD. These studies defined 70-kDa-reactive T cell Ag fine specificities and TCR gene usage in this model. Similar to patients with MCTD, CD4(+) T cells can be readily identified from 70-kDa/U1-RNA-immunized HLA-DR4-transgenic mice. Using both freshly isolated CD4(+) T cells from spleen and lung, and T cell lines, we found that the majority of these T cells were directed against antigenic peptides residing within the RNA-binding domain of 70 kDa. We also found that TCR-beta (TRB) V usage was highly restricted among 70-kDa-reactive T cells, which selectively used TRBV subgroups 1, 2, 6, 8.1, 8.2, and 8.3, and that the TRB CDR3 had conserved sequence motifs which were shared across different TRBV subgroups. Finally, we found that the TRBV and CDR3 regions used by both murine and human 70-kDa-specific CD4(+) T cells were homologous. Thus, T cell recognition of the 70-kDa autoantigen by HLA-DR4-transgenic mice is focused on a limited number of T cell epitopes residing primarily within the RBD of the molecule, using a restricted number of TRBV and CDR3 motifs that are homologous to T cells isolated from MCTD patients.

Sarcoidosis in patients with mixed connective tissue disease: clinical, genetic, serological and histological observations.

The objective of this study was to investigate how the development of sarcoidosis influences the disease course of mixed connective tissue disease (MCTD). The cellular composition of MCTD-associated sarcoidosis granulomas was evaluated and also the disease-accompanying T-cell activation and alterations of the serum cytokine levels were measured before and after the therapy. The HLA-DR specific alleles were also assessed. We present two cases with MCTD coexisting sarcoidosis. Serum concentrations of Th1 and Th2 cytokines were assessed by ELISA. Peripheral blood CD3+ total T-cell numbers, CD4+ and CD8+ T-cell subset were determined by flow cytometry. Furthermore, hematoxylin-eosin staining and immunhistochemistry were performed for histological assessment. HLA-DR specific alleles were determined by using PCR-SSP. Elevated number of activated T-cells and high Th1 cytokine levels were detected, mainly IFN-gamma and TNF-alpha. Histologically, CD4+ and CD8+ T-cells were present in the sarcoidosis infiltrations. The haplotypes were to some extent dissimilar from the HLA-DR genotype from patients with MCTD, or sarcoidosis alone. Sarcoidosis enhances the activation of MCTD, based on the laboratory and clinical findings. Our results show that the inflammation is mainly in the effector phase, while granuloma formation is characteristic of the resolution phase of the disease. The assessment of the cytokine network in sarcoidosis-associated MCTD enables us to select the most effective, individualized therapy protocol for these patients.