Myositis
Abstract # 652 A Novel Dermatomyositis (DM)-Associated Autoantibody Directed Against a 155 kd Protein I Targoff, E Shamim, D Sherry, C Wallace, H Haftel, F Miller, L Rider, The Childhood Myositis Heterogeneity & Intl Myositis Collab Study Grps.
This study investigated novel autoantibodies (Abs) in children and adults with dermatomyositis (DM). Immunoprecipitation (IPP) and standard serologic methods were used to test sera from patients with myositis.
IPP of serum from a DM patient (BR) demonstrated a distinct protein of approximately 155 kd from HeLa cell extract. Screening a large population of children and adults with myositis identified 30 additional sera that IPP a protein of similar size and appearance to BR, often accompanied by a second, much weaker protein of 140 kd that was similar in size to a recently identified anti-MJ Ab. 29/31 patients with anti-155kd had DM, including 9 with adult onset and 20 with juvenile DM (JDM). Five adults had CA-associated DM, and 3 JDM patients had an overlapping autoimmune disease (SLE, LSc, IDDM). Characteristic DM rashes were almost uniformly present. In contrast to patients with anti-synthetases, only 4% had Raynauds, 0% had interstitial lung disease, and 38% had arthritis. Of 13 patients with > 2 years follow-up, 54% had a chronic course, and 23% each had a polycyclic or monocyclic course of illness.
Several defined Abs have been described in polymyositis and DM, but they occur in less than half of adult patients and thus are of limited value clinically. This study describes a new Ab associated with DM, with potential predominance in JDM. This Ab may define a clinical group that is distinct from other myositis-associated Abs. Additional studies of disease specificity/sensitivity are needed to define the clinical and prognostic significance of this Ab.
Abstract # 653 Contribution of IL-17, A T Cell Derived Cytokine, to the Pathogenesis of Dermatomyositis G Chevrel, A Varennes, G Page, H Carrier, R Bouvier, P Miossec. France.
Dermatomyositis is characterized by the infiltration of T cells and macrophages resulting in destruction of muscle fibers. The purpose of this study was to investigate the contribution of soluble factors in the interaction between T cells and myoblasts. ELISA was used to assess the effect of IL-17 (T-cell derived cytokine) and IL-1 (monocyte-produced cytokine) on myoblasts and muscle tissue in culture.
Both rIL-1 and rIL-17 induced IL-6 production by normal myoblasts as measured by ELISA in a dose-dependent manner. After 7 days of culture, unstimulated myoblasts secreted low levels of IL-6. Optimal concentrations of IL-1 and IL-17 increased IL-6 production by myoblasts 68.7-fold and 111.9-fold respectively. When IL-1 and IL-17 were used in combination, IL-6 production was further increased in an additive way. When pieces of intact normal muscle were cultured for 7 days with IL-1 or IL-17 alone, IL-6 production increased 125-fold and 325-fold respectively. Muscle CK release as measured by IFCC method did not increase in the presence of IL-1 or IL-17. Immunostaining of DM muscle biopsies with a goat polyclonal anti-IL-17 antibody demonstrated IL-17 expression in the T lymphocyte rich area in the perimysium.
Editorial Comments:: Although the study shows that IL-17 and IL-1 can influence IL-6 production by myoblasts, the significance of this is unclear, given that these cytokines do not cause direct damage to the myoblasts.
Abstract # 1254 Gene Expression profile of Muscle Biopsies From Patients With Inflammatory Myopathies X Zhou, F Tan, M Xiaon, M Dimachkie, F Arnett. Texas.
The aim of this study was to detect molecular-based changes in muscle biopsy gene expression, including the myositis-associated autoantigens, by using cDNA microarray assays. Total RNA was extracted from frozen muscle biopsies of affected muscles from 7 polymyositis (PM), 3 dermatomyositis (DM) patients and 6 normal controls. After reverse transription and radiolabelling, cDNAs were hybridized to microarray filters spotted with 4000 known human genes, including those of 60 autoantigens, and the results were analyzed using cluster and classification methods.
When compared to controls, muscle biopsies from both PM and DM patients displayed highly expressed genes of HLA-C (p = 0.0008), b-2 microglobulin (p = 0.0054), natural killer cell protein 4 (p = 0.0299), HLA-DR (p = 0.0045) and HLA-DP (p = 0.0003), thymosin b-4 (p = 0.0027) and Ig l(p = 0.038). Increased expression of isoleucine-tRNA synthetase also was found in the 3 DM patients, and glutamyl-prolyl-tRNA synthetase in 2 PM patients. None of the usual myositis-specific autoantigen genes were altered. Additionally, highly up-regulated gene expression levels were consistently shown for collagen type I and III, vimentin and cystatin C, an inhibitor of elastolytic cysteine proteases. In contrast, the genes specifically from fast skeletal muscle including troponin T, tropomyosin 1 and 2, myosin light Chain 1 and actinin-alpha-3 were dramatically down-regulated. Cluster and classification analysis of gene expression identified a set of genes with a myositis specific pattern that achieved disease predictive value of 85% accuracy.
This study demonstrates similar alterations in gene expression profiles in PM and DM muscle biopsises. HLA-class I associated genes, particularly HLA-C and b-2 microglobulin, showed the highest levels of up-regulation (3.8- and 5.4-fold respectively). These data also suggest that muscle dysfunction in PM and DM could be associated with inhibition of some fast skeletal muscle genes. Such alterations in gene expression provide a distinctive myositis profile that may provide insights into molecular diagnosis and advance our understanding of disease pathogenesis.
Editorial Comment: CDNA micro array analysis is a powerful technique to identify novel candidate genes important in the pathogenesis of diseases. The enhanced expression of the HLA Class I genes in PM/DM is extremely interesting in light of the finding of Nagaraju and his colleagues (PNAS 97: 9209) demonstrating autoimmune myositis in mice overexpressing MHC Class I in skeletal muscle.
Abstract # 1257 Expression of Interleukin-1 Alfa in Capillaries and MHC Class I Antigen in Type II Muscle Fibers – Primary Pathogenic Features in Polymyositis and Dermatomyositis Patients I Lundberg, I Nennesmo, L Klareskog, P Nyber. Sweden.
To identify early molecular expression in muscle tissue of patients with polymyositis (PM) and dermatomyositis (DM). 11 patients without detectable inflammatory infiltrates in muscle biopsies but who otherwise fulfilled the Bohan and Peter criteria of probable or definite PM or DM were studied. 7 patients had recent onset myositis and 4 had a relapse of their disease. Duration of clinical symptoms ranged from 1-9 months (median 2 months). 6 patients were diagnosed as PM and 5 as DM, with a median age of 45 years (range 26-64). Muscle tissue from 7 healthy controls was also studied. Immunohistochemistry technique was utilized to identify T cells, macrophages, MHC class I antigen, activation markers of endothelial cells such as ICAM-1, VCAM-1 as well as IL-1a, and IgG, IgM and IgA. Muscle fiber type was defined by ATPase staining. Molecular expression was assessed both by conventional microscopy and by computerized image analysis.
A higher number of capillaries in muscle tissue from patients compared to controls demonstrated IL-1a expression (p < 0.05), and these capillaries were larger and thicker than in the controls. MHC class I expression on muscle fibers was significantly increased in patients compared to the controls as assessed by image analysis (p < 0.005). The MHC class I expression was mainly found on type II muscle fibers. There was no difference in molecular expression between DM and PM with the exception of ICAM-1 which was expressed in a higher number of capillaries in DM patients compared to PM patients.
Editorial Comment: The paucity of MHC Class I expression in normal muscle has been a striking observation. this study correlates nicely with abstract 1254 (above) that showed an increase in MHC Class I expression in myositis patients by CDNA microarray analysis. These data and data from animal models implicate MHC Class I molecules as important in disease pathogenesis.