Expression of calcium-binding proteins MRP8 and MRP14 in inflammatory muscle diseases

The pathophysiological role of infiltrating macrophages and their subtypes in idiopathic inflammatory myopathies such as dermatomyositis, polymyositis, and inclusion body myositis is not fully clear. Monocytes exhibit various phenotypes with different functional properties such as release of pro- or anti-inflammatory mediators. Expression of myeloid-related proteins MRP8 and MRP14, two calcium-binding S100-proteins, characterizes a proinflammatory subtype of macrophages. We immunohistochemically investigated expression of MRP8 and MRP14 in muscle biopsies of 33 patients with dermatomyositis, polymyositis, and inclusion body myositis. We found a clear association of expression of MRP8 and MRP14 by infiltrating macrophages with degeneration of myofibers. Because MRP8 and MRP14 are secreted by activated macrophages we investigated if these proteins would have direct extracellular effects on myocytes. We found that the purified MRP8/MRP14 complex inhibited proliferation and differentiation of C2C12 myoblasts and that it induced apoptosis via activation of caspase-3 in a time- and dose-dependent manner. These results indicate that in the course of inflammatory myopathies, activated macrophages can promote destruction and impair regeneration of myocytes via secretion of MRP8/MRP14.     

Immunocytochemical study of CD45 T cell isoforms in inflammatory myopathies.

The CD45RO and CD45RA antigens subdivide the CD8+ and the CD4+ T cells into primed memory cells and unprimed virgin T cells, respectively. To assess the relative abundance of the CD8+ and the CD4+ T cells expressing the two CD45 isoforms in the major inflammatory myopathies, we immunophenotyped T cells in muscle specimens from patients with inclusion body myositis, polymyositis (PM), and dermatomyositis. The analysis was according to diagnosis and sites of cell accumulation: endomysial inflammatory cells focally surrounding and invading nonnecrotic fibers were analyzed in inclusion body myositis and PM and perivascular infiltrates in PM and dermatomyositis. In all diseases and at all sites of accumulation, the CD45RO+ memory T cells were predominant and the CD45RO/CD45RA ratio exceeded that in normal blood. In PM and inclusion body myositis, the marked enrichment of endomysial T cells in memory cells implicates these cells in the pathogenesis. The enrichment of perivascular T cells in dermatomyositis and PM in memory cells may be a result of enhanced transendothelial migratory capacity of these cells; alternatively, the virgin-to-memory cell conversion may occur after diapedesis.     

Myositiden

Idiopathic inflammatory myopathies (IIM) are diseases that are potentially amenable to immunomodulatory therapy. The challenge for the neuropathologist consists in distinguishing these myopathies from secondary inflammatory myopathies, especially in the context of some muscular dystrophies and metabolic diseases that may also show inflammatory infiltrates. There are generalized IIMs (dermatomyositis, polymyositis, sporadic inclusion body myositis) and focal ones (e.g., proliferative myositis, macrophagic myofasciitis). This review provides diagnostic criteria for each of these and includes pathogenetic mechanisms where available.     

Update on idiopathic inflammatory myopathies

The inflammatory myopathies are a group of acquired diseases, characterized by an inflammatory infiltrate of the skeletal muscle. On the basis of clinical, immuno-pathological and demographic features, three major diseases can be identified: dermatomyositis (DM); polymyositis (PM); and inclusion body myositis (IBM). New diagnostic criteria have recently been introduced, which are crucial for discriminating between the three different subsets of inflammatory myopathies and for excluding other disorders. DM is a complement-mediated microangiopathy affecting skin and muscle. PM and IBM are T cell-mediated disorders, where CD8-positive cytotoxic T cells invade muscle fibres expressing MHC class I antigens, thus leading to fibre necrosis. In IBM, vacuolar formation with amyloid deposits are also present. This article summarizes the main clinical, laboratory, electrophysiological, immunological and histologic features as well as the therapeutic options of the inflammatory myopathies.     

Myopathology of non-infectious inflammatory myopathies - the current status

Besides the classical inflammatory myopathies (IM), dermatomyositis (DM), polymyositis, and inclusion body myositis, the much larger spectrum of IM includes focal and nodular myositis, granulomatous myositis, macrophagic myofasciitis, graft vs. host myositis, eosinophilic myositis, and other immune-associated conditions, some of them only recently described. In addition, paraneoplastic, statin-induced and critical illness myopathies have been considered immune-associated IM. Infectious, i.e., bacterial, viral, and parasitic IM are much less frequent in the northern hemisphere. In IM, muscle biopsy is an essential diagnostic procedure to initiate therapy. The myopathological spectrum encompasses disease-specific histopathological features, such as perifascicular atrophy in DM, non-necrotizing granulomas in sarcoid myopathy, autophagic vacuoles with tubulofilamentous inclusions in inclusion body myositis, rarely electron microscopic criteria, such as undulating tubules in endothelial cells of DM specimens, and, foremost, immunohistochemical findings. These latter features concern inflammatory infiltrates, the muscle parenchyma, the interstitial compartment, and the vasculature with varying involvement of each component in the different IM. Differences in immunohistochemical parameters among the IM, such as major histocompatibility complexes I and II, cytokines, cell adhesion molecules, different types of inflammatory cells, metalloproteinases, and complement factors procure a large gamut of data, the individual patterns of which characterize the myopathology of individual IM.     

The pathological diagnosis of specific inflammatory myopathies.

Pathological diagnosis of dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM) should be possible in almost all cases when an appropriately involved muscle is biopsied. DM shows characteristic patterns of muscle fiber damage and capillary damage. Lymphocytes and macrophages are seen in PM and IBM partially invading non-necrotic fibers. IBM is also characterized by rimmed vacuoles with membranous whorls, characteristic masses of filaments in cytoplasm and sometimes in nuclei, and grouped atrophic fibers. Muscle fiber damage in PM is more variable. Inflammatory myopathy can be associated with HTLV-1 and HIV infection. In the latter a strong resemblance to PM is reported. Separate, still less well characterized forms of inflammatory myopathy occur in young children.     

Skeletal muscle fibers express major histocompatibility complex class II antigens independently of inflammatory infiltrates in inflammatory myopathies

The aim of our study was to address the question of whether muscle fibers express major histocompatibility complex (MHC) class II in inflammatory myopathies. For this purpose we performed a systematic study of MHC class II antigen expression on muscle fiber membranes in muscle tissue from polymyositis and dermatomyositis patients in various stages of disease activity. Thirty-two patients with classical clinical signs of myositis were divided into subgroups depending on duration of clinical signs of myositis and presence or absence of inflammatory infiltrates in muscle tissue. Immunohistochemistry as well as double-immunofluorescence stainings were used to identify the presence of MHC class II in muscle tissue. MHC class I was included for comparison. Quantification of positive staining was performed using an image analysis system in addition to evaluation by manual microscopic scoring and laser confocal microscopy. It was demonstrated that a significant proportion of skeletal muscle fibers in inflammatory myopathies express MHC class II as well as MHC class I and that MHC antigen expression is independent of the inflammatory cell infiltration. Furthermore, there were no differences in staining pattern between polymyositis and dermatomyositis patients. Our results indicate that MHC class II and MHC class I molecules may be involved in initiating and maintaining the pathological condition in myositis rather than only being a consequence of a preceding local inflammation.     

Recent advances in the morphology of myositis

Myositis in man may be divided into infectious and non-infectious forms. The myopathologist more often deals with the latter forms which comprise dermatomyositis/polymyositis, inclusion body myositis, mixed connective tissue disease/collagenoses, and granulomatous myopathies. Modern morphological techniques as enzyme-histochemistry, electron microscopy, immunohistology, and morphometry are of different value in various forms of myositis, but are often indispensable techniques in up-to-date diagnostic work up of a myositis.     

Identification of a novel myositis-associated antibody directed against cortactin

Objective

The aim of this study is to describe a novel myositis-associated autoantibody (anti-cortactin antibody) and assess related clinical and immunological manifestations and its clinical significance.

Methods

Adult patients with myositis (dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, and inclusion body myositis), as well as patients with other autoimmune diseases and non-inflammatory myopathies were analyzed for the presence of anti-cortactin antibody using in-house developed ELISA and immunoblotting techniques with a commercial source of purified cortactin. The cut-off for positive status was determined in a group of healthy volunteers.

Results

Antibody against cortactin was positive in 7/34 (20%) polymyositis patients, 9/117 (7.6%) dermatomyositis, 2/7 (26%) immune-mediated necrotizing myopathy, and none of the 4 patients with inclusion body myositis. The antibody also tested positive in 3/101 patients with other autoimmune diseases (2 systemic sclerosis and 1 systemic lupus erythematosus), and in 1/29 patients with non-inflammatory myopathy. No relevant association with specific clinical features was found in patients with these antibodies. Anti-cortactin antibody was more frequently positive in patients with polymyositis and immune-mediated necrotizing myopathy than in the remaining myositis patients, and was the only myositis autoantibody found in sera of 3 patients from these groups.

Conclusions

Our data indicate that cortactin is a novel target antigen in patients with autoimmune diseases, especially patients with polymyositis or immune-mediated necrotizing myopathy. Anti-cortactin can be considered a new myositis-associated antibody.     

Idiopathic Inflammatory Myopathies

The idiopathic inflammatory myopathies include polymyositis and dermatomyositis, which tend to be responsive to drug therapy, and inclusion body myositis, which is often unresponsive or only partially responsive to drugs. Corticosteroids are considered the first line treatment of these disorders, and as well as being anti-inflammatory are immunosuppressive when used at dosages above prednisolone 20 mg/day or equivalent. In those patients who are refractory to corticosteroids, or are prone to develop complications from corticosteroids, second line drugs such as methotrexate, azathioprine or intravenous immunoglobulin should be introduced. These therapies tend to be slow acting, but response often occurs in 4 to 6 weeks and allows the dosage of corticosteroid to be reduced more rapidly. In those occasional patients with inflammatory myopathies that are refractory to corticosteroids and second line agents, one should consider adding in a third line agent such as cyclosporin, chlorambucil or cyclophosphamide. Although most clinicians would use these immunosuppressive drugs singly in combination with corticosteroids, multiple drug therapy should be considered in severe refractory cases.     

Local T-Cell Proliferation and Differentiation in Inflammatory Myopathies

Our objective was to investigate the patterns of proliferation and differentiation of infiltrating cells in inflammatory myopathies. Immunohistochemical staining was performed on muscle biopsy specimens from 18 patients with inclusion body myositis, polymyositis and dermatomyositis using monoclonal and polyclonal antibodies.
An abundance of cells were TNF-α⁺ (4–8%), ICAM-1⁺ (7–65%). IFN-γ⁺ (3–6%), and Ki-67⁺ (4–8%). It was shown that 70% of the Ki-67⁺ cells were Ki-67⁺CD3⁺ cells. Very few mononuclear cells were IL-2R⁺. MHC-I expression was found on nearly all muscle fibres in all cases, while MHC-II expression was found on occasional muscle fibres in 1/3 of cases. Analysis of repeated biopsies from four IBM patients after prednisolone treatment showed no change in the proportions of TNF-α, ICAM-1, IFN-γ or Ki-67 positive cells. In inflammatory myopathies there is an intense proliferation and differentiation of inflammatory cells in situ , indicating a local stimulation of the inflammatory process.     

Diagnosis,pathogenesis and treatment of myositis: recent advances

Dermatomyositis (DM), polymyositis (PM), necrotizing myopathy (NM) and inclusion body myositis (IBM) are four distinct subtypes of idiopathic inflammatory myopathies – in short myositis. Recent studies have shed some light on the unique pathogenesis of each entity. Some of the clinical features are distinct, but muscle biopsy is indispensable for making a reliable diagnosis. The use of magnetic resonance imaging of skeletal muscles and detection of myositis‐specific autoantibodies have become useful additions to our diagnostic repertoire. Only few controlled trials are available to substantiate current treatment approaches for myositis and hopes are high that novel modalities will become available within the next few years. In this review we provide an up‐to‐date overview of the pathogenesis and diagnostic approach of myositis. We aim to present a guide towards therapeutic and general management.     

Pathogenesis and therapies of immune-mediated myopathies

The most common autoimmune muscle disorders include dermatomyositis (DM), polymyositis (PM), necrotizing autoimmune myositis (NAM) and sporadic inclusion body myositis (sIBM). DM is a complement-mediated microangiopathy leading to destruction of capillaries, hypoperfusion and inflammatory cell stress on the perifascicular regions. NAM is an increasingly recognized subacute myopathy triggered by statins, viral infections, cancer or autoimmunity with macrophages as the final effector cells causing fiber injury. PM and IBM are T cell-mediated disorders where cytotoxic CD8(+) T cells clonally expand in situ and invade major histocompatibility complex class I expressing muscle fibers. In sIBM, in addition to autoreactive T cells, there are degenerative features characterized by vacuolization and accumulation of stressor or amyloid-related misfolded proteins; an interrelationship between inflammatory and degeneration-associated molecules is prominent and enhances the cascade of pathogenic factors. These disorders are treatable, hence the need to make the correct diagnosis from the outset. The applied therapeutic strategies are outlined and the promising new agents are reviewed.     

Skeletal muscle in polymyositis. Immunohistochemical study.

Thirty-two patients with adult-onset polymyositis uncomplicated by cancer or systemic connective tissue disease were studied. Muscle biopsy specimens were examined with direct immunofluorescence microscopy and results were compared with those in 94 control subjects. Sarcolemmal and sarcoplasmic staining were observed in both groups and considered to be nonspecific. Immune deposits in the muscle microvasculature were present in some cases of systemic lupus erythematosus and dermatomyositis but were not present in polymyositis. Our data suggest that the finding of vascular immunofluorescence excludes the diagnosis of adult polymyositis and implies that the pathogenesis of this disease and other idiopathic inflammatory myopathies may differ.     

Anti-Jo-1 antibody positive polymyositis—successful therapy with leflunomide

Idiopathic inflammatory myopathies (IM), including dermatomyositis (DM) and polymyositis (PM), are a group of systemic rheumatologic diseases of unknown etiology characterized by chronic myositis. Antisynthetase antibodies such as the anti-Jo-1 antibody are known to be highly specific for inflammatory myopathies. Patients with this antibody frequently show a combination of symptoms including interstitial lung disease, fever, polyarthritis, myositis, Raynaud's phenomenon and “mechanic's hands”. In the management of PM with anti-Jo-1 antibody, immunosuppressive agents are used to control the disease. Leflunomide is a new immunosuppressive drug recently introduced in the treatment of rheumatoid and psoriatic arthritis. Here, we report two cases of female patients with PM and anti-Jo-1 antibodies, who were successfully treated with leflunomide.     

Anti-Jo-1 antibody positive polymyositis--successful therapy with leflunomide

Idiopathic inflammatory myopathies (IM), including dermatomyositis (DM) and polymyositis (PM), are a group of systemic rheumatologic diseases of unknown etiology characterized by chronic myositis. Antisynthetase antibodies such as the anti-Jo-1 antibody are known to be highly specific for inflammatory myopathies. Patients with this antibody frequently show a combination of symptoms including interstitial lung disease, fever, polyarthritis, myositis, Raynaud's phenomenon and "mechanic's hands". In the management of PM with anti-Jo-1 antibody, immunosuppressive agents are used to control the disease. Leflunomide is a new immunosuppressive drug recently introduced in the treatment of rheumatoid and psoriatic arthritis. Here, we report two cases of female patients with PM and anti-Jo-1 antibodies, who were successfully treated with leflunomide.     

Immune checkpoint failures in inflammatory myopathies: An overview

Dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), immune mediated necrotizing myopathy (IMNM) and overlap myositis (OM) are classified as inflammatory myopathies (IM) with involvement of autoimmune features such as autoreactive lymphocytes and autoantibodies. Autoimmunity can be defined as a loss in self-tolerance and attack of autoantigens by the immune system. Self-tolerance is achieved by a group of immune mechanisms occurring in central and periphal lymphoid organs and tissues, called immune checkpoints, that work in synergy to protect the body from harmful immune reactions. Autoimmune disorders appear when immune checkpoints fail. In this review, the different immune checkpoint failures are discussed in DM, PM, IBM and IMNM. Exploring research contribution in each of these immune checkpoints might help to highlight research perspectives in the field and obtain a more complete picture of IM disease pathology.     

Immunohistochemical characterization of the mononuclear cells infiltrating muscle of patients with inflammatory and noninflammatory myopathies

The immunopathogenetic mechanisms associated with the development of inflammatory myopathies are not well defined. In order to identify cells in affected muscle tissue, mononuclear cells infiltrating muscle biopsies from patients with inflammatory myopathies and controls with other neuromuscular diseases were analyzed in situ by an avidin-biotin immunoperoxidase technique. Serial frozen sections were stained for cells expressing total T, helper-induced T, suppressor-cytotoxic T, B, monocyte/macrophage, and HLA-DR phenotypes. A significant increase in the percentage of helper-inducer T cells are noted in the inflammatory myopathies when compared to the disease control group. Furthermore, most of the mononuclear cells in the inflammatory myopathy biopsies were HLA-DR positive, suggesting that the infiltrating T lymphocytes were activated. No significant differences in mononuclear cell distributions were found when the inflammatory myopathy group was broken down into individual groups of patients with polymyositis, polymyositis with associated connective tissue disease, and dermatomyositis.     

Can tissue transglutaminase be a marker of idiopathic inflammatory myopathies?

In the normal striated muscle, tissue transglutaminase (TG2) content is vestigial. However, this protein's presence has been reported to occur in myoblasts and myotubes during the fetal period. Its increased expression has been also found in the muscle tissue in the course of sporadic inclusion body myositis, as well as in polymyositis (PM) and dermatomyositis (DM), which are considered to be diseases of immunological origin. Based on in vitro studies, a substantial TG2 role in the infiltration of some T cell subsets into inflamed tissues has been suggested lately. In this study, the immunohistochemical reactions in the guinea pig experimental myositis specimens and in the ones from PM/DM patients were compared. The guinea pig tissue specimens were taken from muscles affected by experimental myositis induced by intramuscular injections of: 1/sera from 30 neoplasm patients with no metastases; 2/sera from 10 healthy people; 3/sera from 2 DM patients; 4/neuropeptides (SP, NPY or VIP) and from 5/the muscles affected by the reversed passive Arthus reaction (RPAR). The immunostaining for TG2 revealed substantial presence of this protein in single, damaged muscle fibers and a weak reaction in regenerating fibers appearing in PM/DM patients' specimens. From among experimental myositis specimens, a very intensive reaction appeared only in the damaged and regenerating muscle fibers present in the slides from guinea pig muscles injected with DM patients' sera. Such results suggest some presence of a specific factor(s) (the one(s) responsible for TG2 expression in the damaged muscle fibers) in DM patients' sera. The results suggest that transglutaminase can be a marker of inflammatory myopathies. A probable correlation between TG2 expression in muscles and organismal immunological factors, including the complement activation status, requires additional studies.