Clinical relevance of autoantibodies in systemic rheumatic diseases

Autoantibodies directed to intracellular antigens are serological hallmarks of systemic rheumatic diseases. Identification of circulating autoantibodies is helpful in establishing the correct diagnosis, indicating the prognosis and providing a guide to treatment and follow-up. Some autoantibodies are included in diagnostic and classification criteria for diseases such as anti-Sm antigen and anti-double-stranded DNA antibodies in systemic lupus erythematosus, anti-U1 nuclear ribonucleoprotein antibodies in mixed connective tissue disease, and anti-SS-A/Ro and anti-SS-B/La antibodies in Sjögren's syndrome. Over the past 30 years, the identification of new autoantibody systems was advanced by the initiation or adaptation of novel techniques such as double immunodiffusion to detect antibodies to saline-soluble nuclear antigens, extraction-reconstitution and ELISA techniques to detect histone and chromatin antibodies, immunoblotting and immunoprecipitation to detect a wide range of antibodies directed against naturally occurring and recombinant proteins. These techniques have been made possible by advances in cellular and molecular biology and in turn, the sera from index patients have been important reagents to identify novel intracellular macromolecules. This paper will focus on the clinical relevance of several autoantibody systems described by Tan and his colleagues over the past 30 years.Abbreviations ANA antinuclear antibody - CENPs centromere proteins - CTD connective tissue disease - DIA drug-induced autoimmunity - DIL drug-induced lupus - HIV human immunodeficiency virus - IIF indirect immunofluorescence - JCA juvenile chronic arthritis - MCTD mixed connective tissue disease - MSA mitotic spindle apparatus - NOR nucleolar organizer - NuMA nuclear mitosis antigen - PBC primary biliary cirrhosis - PCNA proliferating cell nuclear antigen - PM polymyositis - RA rheumatoid arthritis - RNP ribonucleoprotein - SLE systemic lupus erythematosus - SS Sjögren's syndrome - SSc systemic sclerosis - UCTD undifferentiated connective tissue disease     

5-Methylcytosine content of DNA in blood, synovial mononuclear cells and synovial tissue from patients affected by autoimmune rheumatic diseases

The percentage of 5-methylcytosine (m⁵Cyt) has been determined in peripheral blood, synovial mononuclear cells and synovial tissue from patients affected by various rheumatic autoimmune diseases. The determination was performed by reversed-phase high-performance liquid chromatography. Fifteen controls were compared to twenty-one patients affected by rheumatoid arthritis and to nine patients affected by systemic lupus erythematosus. The mean percentage of m⁵Cyt in normal individuals was significantly higher than in the rheumatoid arthritis and systemic lupus erythematosus patients. In addition, patients with active disease showed lower values than patients in remission. This finding is in agreement with the hypothesis that DNA hypomethylation may play a role in the pathogenesis of the autoimmune diseases, resulting in altered oncogen expression. Therapy with cyclosporin A led to a decrease in the percentage of m⁵Cyt in three rheumatoid arthritis patients, but a rebound was observed when the cyclosporin A was suspended. The percentage of m⁵Cyt in the DNA of synovial tissue from four rheumatoid arthritis patients and five patients with osteoarthritis was similar; this observation confirms that, in addition to disease-specific and disease activity-specific variations, the percentage of m⁵Cyt may also show tissue-specific variations.     

Rheology of synovial fluid

After a discussion of the role of synovial fluid as a joint lubricant, rheological measurements are described with both normal (healthy) synovial fluids and pathological ones. Shear stress and first normal stress difference are measured as a function of shear gradient to calculate the apparent shear viscosity eta 1 and the apparent normal viscosity psi 7 as well as an apparent shear modulus G'. It is found, that in case of diseased synoviae all rheological parameters deteriorate. Most significant changes are observed with the zero shear viscosity eta 0, the shear modulus G', and a characteristic time theta 1, which is the reciprocal of the critical shear rate Dc which determines the onset of shear thinning. The rheological deterioration of synovial fluids is explained in terms of solute structure, whereby a molecular mass of the backbone hyaluronic acid of at least 10(7) g.mol-1 is required for satisfactory function. A theory of the rheological performance of normal synovial fluid as well as its pathological deterioration is proposed.     

Stem cell transplantation for rheumatic autoimmune diseases

Immunoablative therapy and hematopoietic stem cell transplantation (HSCT) is an intensive treatment modality aimed at 'resetting' the dysregulated immune system of a patient with immunoablative therapy and allow outgrowth of a nonautogressive immune system from reinfused hematopoietic stem cells, either from the patient (autologous HSCT) or a healthy donor (allogeneic HSCT). HSCT has been shown to induce profound alterations of the immune system affecting B and T cells, monocytes, and natural killer and dendritic cells, resulting in elimination of autoantibody-producing plasma cells and in induction of regulatory T cells. Most of the available data have been collected through retrospective cohort analyses of autologous HSCT, case series, and translational studies in patients with refractory autoimmune diseases. Long-term and marked improvements of disease activity have been observed, notably in systemic sclerosis, systemic lupus erythematosus, and juvenile idiopathic arthritis, and treatment-related morbidity and mortality have improved due to better patient selection and modifications of transplant regimens. Treatment-related mortality has decreased to approximately 7%. Prospective, randomised, controlled clinical trials are ongoing or planned in systemic sclerosis, systemic lupus erythematosus, and several nonrheumatological conditions.     

Perspectives on epigenetic-based immune intervention for rheumatic diseases

Rheumatic disease can loosely be described as any painful condition affecting the loco-motor system, including joints, muscles, connective tissues, and soft tissues around the joints and bones. There is a wide spectrum of rheumatic diseases, many of which involve autoimmunity, including systemic lupus erythematosus and rheumatoid arthritis. A significant body of evidence now links aberrant epigenetic regulation of gene expression with rheumatic disease and points toward the use of epigenetic targeting agents as potential new treatment options, particularly for those conditions associated with an autoimmune element. In this perspective, I will briefly cover the current knowledge surrounding this area in the field of rheumatology.     

Clinical value of whole-body PET/CT in patients with active rheumatic diseases

Advanced imaging techniques may enable early diagnosis and monitoring of therapy in various rheumatic diseases. To prevent irreversible tissue damage, inflammatory rheumatic disease must be diagnosed and treated in pre-clinical stages, requiring highly sensitive detection techniques. Positron emission tomography (PET) provides highly sensitive, quantitative imaging at a molecular level, revealing the important pathophysiological processes underlying inflammation. This review provides an overview of the current utility of ¹⁸ F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT) in patients with active rheumatic diseases such as rheumatoid arthritis, spondyloarthritis, polymyalgia rheumatica, adult-onset Still’s disease, relapsing polychondritis, immunoglobulin G4-related disease, large-vessel vasculitis, Wegener’s granulomatosis, polymyositis, and dermatomyositis. We also discuss the role of FDG-PET/CT in the diagnosis and monitoring of these diseases.     

Clinical value of whole-body PET/CT in patients with active rheumatic diseases

Advanced imaging techniques may enable early diagnosis and monitoring of therapy in various rheumatic diseases. To prevent irreversible tissue damage, inflammatory rheumatic disease must be diagnosed and treated in pre-clinical stages, requiring highly sensitive detection techniques. Positron emission tomography (PET) provides highly sensitive, quantitative imaging at a molecular level, revealing the important pathophysiological processes underlying inflammation. This review provides an overview of the current utility of ¹⁸?F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT) in patients with active rheumatic diseases such as rheumatoid arthritis, spondyloarthritis, polymyalgia rheumatica, adult-onset Still’s disease, relapsing polychondritis, immunoglobulin G4-related disease, large-vessel vasculitis, Wegener’s granulomatosis, polymyositis, and dermatomyositis. We also discuss the role of FDG-PET/CT in the diagnosis and monitoring of these diseases.     

Degradation products of fibrinogen in synovial fluid

The fibrin/fibrinogen degradation products were measured in 24 synovial fluids sampled from patients with knee joint effusion. It has been observed that they are increased in synovial fluid involved in inflammatory processes. Their presence and concentration seem to be related to the control of local inflammation.     

Proteomic analysis of human osteoarthritis synovial fluid

Background

Osteoarthritis is a chronic musculoskeletal disorder characterized mainly by progressive degradation of the hyaline cartilage. Patients with osteoarthritis often postpone seeking medical help, which results in the diagnosis being made at an advanced stage of cartilage destruction. Sustained efforts are needed to identify specific markers that might help in early diagnosis, monitoring disease progression and in improving therapeutic outcomes. We employed a multipronged proteomic approach, which included multiple fractionation strategies followed by high resolution mass spectrometry analysis to explore the proteome of synovial fluid obtained from osteoarthritis patients. In addition to the total proteome, we also enriched glycoproteins from synovial fluid using lectin affinity chromatography.

Results

We identified 677 proteins from synovial fluid of patients with osteoarthritis of which 545 proteins have not been previously reported. These novel proteins included ADAM-like decysin 1 (ADAMDEC1), alanyl (membrane) aminopeptidase (ANPEP), CD84, fibulin 1 (FBLN1), matrix remodelling associated 5 (MXRA5), secreted phosphoprotein 2 (SPP2) and spondin 2 (SPON2). We identified 300 proteins using lectin affinity chromatography, including the glycoproteins afamin (AFM), attractin (ATRN), fibrillin 1 (FBN1), transferrin (TF), tissue inhibitor of metalloproteinase 1 (TIMP1) and vasorin (VSN). Gene ontology analysis confirmed that a majority of the identified proteins were extracellular and are mostly involved in cell communication and signaling. We also confirmed the expression of ANPEP, dickkopf WNT signaling pathway inhibitor 3 (DKK3) and osteoglycin (OGN) by multiple reaction monitoring (MRM) analysis of osteoarthritis synovial fluid samples.

Conclusions

We present an in-depth analysis of the synovial fluid proteome from patients with osteoarthritis. We believe that the catalog of proteins generated in this study will further enhance our knowledge regarding the pathophysiology of osteoarthritis and should assist in identifying better biomarkers for early diagnosis.