The Assessment of Major Histocompatibility Complex (MHC) Class-I Expression in Different Neuromuscular Diseases.

Background: Major histocompatibility complex (MHC) class-1 antigen is a glycoprotein expressed in all nucleated cells. The aim of this study was to assess MHC class-I expression in different neuromuscular diseases. Methods: The authors reviewed the data of 54 patients with neuromuscular diseases. Anti MHC class-I antibody was performed on the frozen muscle tissues using immunohistochemistry. MHC class-I was scored based on its expression on muscle fibers (0: normal, 1: expression <5 fibers, 2: expression in 5-10 fibers, 3: expression in >10 fibers). The pattern was only assessed in cases with MHC class-I scored 3 as: (1: Sarcocapillary, 2: Sarcocapillary and necrotic fibers, 3: Perifascicular). The relationship between MHC classI expression and neuromuscular diseases was statistically analyzed. Results: The mean age of the patients was 39.1 +/- 18.5 years. Around 50% of patients showed normal CK levels and 5% of the cases showed elevated CK levels. There was a significance difference in MHC class-I expression between cases with normal and elevated CK levels when MHC class-I score was 3 (p= 0.020). There was a significant difference in MHC class-I expression among different neuromuscular diseases (p<0.001). All cases with idiopathic inflammatory myopathies (IIMs) have expressed MHC class-I in more than 10 fibers. MHC class-I was expressed in 15 cases of non-IIMs. Conclusion: MHC class-I cannot be solely used as a biomarker to distinguish IIMs from non-IIMs. The presence of MHC class-I molecules in non-IIMs might be related to immunoproteasomes mechanism. Further studies, with different muscle proteins expression and genomic sequencing, must be conducted to understand the role of MHC Class-I in neuromuscular diseases.