Temporal alterations of immunohistochemical findings in polymyositis

Expression of CD163 and major histocompatibility complex class I as diagnostic markers for idiopathic inflammatory myopathies

BACKGROUND

To develop an inflammation-related immunohistochemistry marker-based algorithm that confers higher diagnostic ability for idiopathic inflammatory myopathies (IIMs) than IIM-related histopathologic features.

METHODS

Muscle biopsy tissues from 129 IIM patients who met the 2017 EULAR/ACR criteria and 73 control tissues from patients with non-inflammatory myopathies or healthy muscle specimens were evaluated for histological features and immunostaining results of CD3, CD4, CD8, CD20, CD68, CD163, MX1, MHC class I, MHC class II, and HLA-DR. Diagnostic algorithms for IIM were developed based on the results of the classification and regression tree (CART) analysis, which used immunostaining results as predictor variables for classifying patients with IIMs.

RESULTS

In the analysis set (IIM, n = 129; control, n = 73), IIM-related histopathologic features had a diagnostic accuracy of 87.6% (sensitivity 80.6%; specificity 100.0%) for IIMs. Notably, muscular expression of CD163 (99.2% vs. 20.8%, p < 0.001) and MHC class I (87.6% vs. 23.1%, p < 0.001) was significantly higher in the IIM group than in controls. Based on the CART analysis results, we developed an algorithm combining CD163 and MHC class I expression that conferred a diagnostic accuracy of 95.5% (sensitivity 96.1%; specificity 94.5%). In addition, our algorithm was able to correctly diagnose IIM in 94.1% (16/17) of patients who did not meet the 2017 EUALR/ACR criteria but were diagnosed as having IIMs by an expert physician.

CONCLUSIONS

Combination of CD163 and MHC class I muscular expression may be useful in diagnosing IIMs.

An analysis of the sensitivity and specificity of MHC-I and MHC-II immunohistochemical staining in muscle biopsies for the diagnosis of inflammatory myopathies

Although there have been several previous reports of immunohistochemical staining for MHC antigens in muscle biopsies, there appears to be a lack of consensus about its routine use in the diagnostic evaluation of biopsies from patients with suspected inflammatory myopathy. Positive MHC-I staining is nonspecific but is widely used as a marker for inflammatory myopathy, whilst the role of MHC-II staining is not clearly defined. We investigated the sensitivity and specificity of MHC-I and MHC-II immunostaining for the diagnosis of inflammatory myopathy in a large group of biopsies from a single reference laboratory. Positive staining for MHC-I was found to have a high sensitivity in biopsies from patients with inflammatory myopathy but a very low specificity, as it was also common in other non-inflammatory myopathies and neurogenic disorders. On the other hand, MHC-II positivity had a much higher specificity in all major subgroups of inflammatory myopathy, especially inclusion body myositis. The findings indicate that the combination of MHC-I and MHC-II staining results in a higher degree of specificity for the diagnosis of inflammatory myopathy and that in biopsies with inflammation, positive MHC-II staining strongly supports the diagnosis of an immune-mediated myopathy. We recommend that immunohistochemical staining for both MHC-I and MHC-II should be included routinely in the diagnostic evaluation of muscle biopsies from patients with suspected inflammatory myopathy. However, as the sensitivity and interpretation of MHC staining may depend on the technique used, further studies are needed to compare procedures in different centres and develop standardised protocols.

Essential muscle pathology for the rheumatologist

This review introduces/refreshes some basic histopathologic methods and findings of skeletal muscle biopsies with emphasis on those diseases commonly encountered in a rheumatologist's practice. The 3 general areas of myopathology discussed are metabolic myopathies, toxic myopathies, and inflammatory myopathies. The authors, neuropathologists, hope to provide in this article what they think are some commonalities and disease-specific methods in their pathologic workup as well as a practical approach to the collaboration that pathologists undertake with their rheumatology colleagues to come to a working diagnosis.

Idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies are a group of systemic autoimmune syndromes characterized by striated muscle inflammation. Here, we discuss the clinical features of this group of conditions and review the recent developments in the understanding of the pathogenesis and immunogenetics of the idiopathic inflammatory myopathies. The role of myositis-specific autoantibodies and their clinical significance and an overview of management are also provided.

Upregulation of MHC class I in transgenic mice results in reduced force-generating capacity in slow-twitch muscle

Expression of major histocompatibility complex (MHC) class I in skeletal muscle fibers is an early and consistent finding in inflammatory myopathies. To test if MHC class I has a primary role in muscle impairment, we used transgenic mice with inducible overexpression of MHC class I in their skeletal muscle cells. Contractile function was studied in isolated extensor digitorum longus (EDL, fast-twitch) and soleus (slow-twitch) muscles. We found that EDL was smaller, whereas soleus muscle was slightly larger. Both muscles generated less absolute force in myopathic compared with control mice; however, when force was expressed per cross-sectional area, only soleus muscle generated less force. Inflammation was markedly increased, but no changes were found in the activities of key mitochondrial and glycogenolytic enzymes in myopathic mice. The induction of MHC class I results in muscle atrophy and an intrinsic decrease in force-generation capacity. These observations may have important implications for our understanding of the pathophysiological processes of muscle weakness seen in inflammatory myopathies. Muscle Nerve, 2008.

Advances in the immunopathophysiology of the idiopathic inflammatory myopathies: Not as simple as suspected

In the past three decades, not much has changed in the pathophysiologic concepts of dermatomyositis and polymyositis. However, in the past couple of years, many changes have occurred reflecting the extremely complex nature of the immune response in general. New pathophysiologic models are needed, but at present, none of them encompasses all the recent findings. The changing concepts of dermatomyositis and polymyositis offer new opportunities for unraveling these diseases and developing better strategies for prevention and treatment. This article discusses the most important developments and their methodologic short-comings.

Role of major histocompatibility complex class I molecules in autoimmune myositis

PURPOSE OF REVIEW

Recent work has continued to clarify the role of major histocompatibility complex class I in the pathogenesis of autoimmune myositis. In the past year, several new observations have been made in this area. This review describes these findings and discusses their relevance to the pathogenesis of autoimmune myositis.

RECENT FINDINGS

Recent studies have confirmed earlier observations of the up-regulation of major histocompatibility complex class I antigens in myositis. In particular, a recent study has strengthened the conclusion that major histocompatibility complex class I expression is highly specific to inflammatory myopathies and may be of diagnostic value. Two new studies have indicated that endoplasmic reticulum stress response pathway (the endoplasmic reticulum overload [NF-kB] and unfolded protein response [GRP78]) are highly activated in patients with myositis. One study using transgenic mice has further indicated that abnormal accumulation of major histocompatibility complex class I in the endoplasmic reticulum of muscle may be responsible for the initiation of this endoplasmic reticulum stress response. Furthermore, studies of normal muscle cells have shown that endoplasmic reticulum stress also plays an important role in skeletal muscle development. Investigations of autoantigen expression in myositis biopsies have revealed that regenerating muscle cells express high levels of autoantigens and major histocompatibility complex class I, indicating that these cells are the targets of cytotoxic T-cell attack and may participate in the initiation of a myositis-specific autoimmune response.

SUMMARY

Defining the role of major histocompatibility complex class I in autoimmune myositis may be useful not only for diagnosis of this group of diseases but also for therapeutic opportunities for these difficult disorders.

Activation of the endoplasmic reticulum stress response in autoimmune myositis: potential role in muscle fiber damage and dysfunction

OBJECTIVE

The etiology and pathogenesis of human inflammatory myopathies remain unclear. Findings of several studies suggest that the degree of inflammation does not correlate consistently with the severity of clinical disease or of structural changes in the muscle fibers, indicating that nonimmune pathways may contribute to the pathogenesis of myositis. This study was undertaken to investigate these pathways in myositis patients and in a class I major histocompatibility complex (MHC)-transgenic mouse model of myositis.

METHODS

We examined muscle tissue from human myositis patients and from class I MHC-transgenic mice for nonimmune pathways, using biochemical, immunohistochemical, and gene expression profiling assays.

RESULTS

Up-regulation of class I MHC in skeletal muscle fibers was an early and consistent feature of human inflammatory myopathies. Class I MHC staining in muscle fibers of myositis patients showed both cell surface and a reticular pattern of internal reactivity. The pathways of endoplasmic reticulum (ER) stress response, the unfolded protein response (glucose-regulated protein 78 pathway), and the ER overload response (NF-kappaB pathway) were significantly activated in muscle tissue of human myositis patients and in the mouse model. Ectopic expression of wild-type mouse class I MHC (H-2K(b)) but not degradable glycosylation mutants of H-2K(b) induced ER stress response in C(2)C(12) skeletal muscle cells.

CONCLUSION

These results indicate that the ER stress response may be a major nonimmune mechanism responsible for skeletal muscle damage and dysfunction in autoimmune myositis. Strategies to interfere with this pathway may have therapeutic value in patients with this disease.

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.