Pathogenesis and treatment of myasthenia gravis

Lymphocyte subsets and viruses were examined in the thymuses and thymomas of patients with myasthenia gravis (MG). Most of the lymphocytes were considered to be from cortical thymocytes since they were positive for OKT4, 6, 8 and 10. Retrovirus-like particles were detected in the thymuses and thymomas from patients with MG. These data suggest contributions of lymphocytes and viruses in the pathogenesis of MG. HLA antigen frequencies in 49 patients with MG were studied to investigate a genetic background. Although the association of HLA-B8, DR3, DRw52 haplotype with Caucasian MG has been reported, Japanese MG seems to be associated with a different haplotype, HLA-B39, Cw7, DRw8. To achieve a better understanding of the association of HLA with MG, analysis of restriction fragment length polymorphism (RFLP) of DNA from MG patients was performed. When DQ beta cDNA probe was used, the increased frequency of PstI 12 kilobase fragment was observed in HLA-DR2 positive patients compared to healthy DR2 positives. For treating MG patients, we have been utilizing low-dose prednisolone (PSL) or high-dose gammaglobulin. Our results so far indicate that low-dose PSL seems to be as effective as high-dose PSL therapy, however, we could not observe any favorable effect of high-dose gammaglobulin therapy on MG.