Immune Characterization of a Vietnamese Cohort With Idiopathic Inflammatory Myopathies.

Introduction/aims: Idiopathic inflammatory myopathies (IIMs) are classified into five subtypes that are associated with distinct groups of myositis-specific antibodies (MSAs). Variations in the prevalence, genetic predisposition and clinical manifestations exist in patients with IIM from different ethnic backgrounds. In this study, we aimed to characterize the immunopathological changes in muscle tissue and serum cytokines in a Vietnamese IIM cohort with Kinh ethnicity.

Methods: Muscle biopsies, sera, clinical data, and autoantibody profiles from 64 patients with IIM were included. Muscles were stained by immunohistochemistry using antibodies that target immune cells and molecules. Serum cytokines were measured by multiplex bead arrays. Clustering analysis was performed using the partitioning around medoids algorithm.

Results: The anti-MDA5 antibody was the most common MSA in this cohort (15.6%), followed by anti-Jo-1 (10.9%). A wide range of clinical manifestations and immunohistological features were seen within the serologically defined subgroups. There was no difference in the levels of immune cells, capillary density or dilation, or patterns of C5b-9 expression between the myositis subgroups. MHC-I patterns were the only immunomorphological variable that was different in these subgroups. IP-10, IL-17A, and APRIL were increased in patients with IIM compared to healthy controls (p = 5.7 × 10^-3, 6.9 × 10^-4, 2.4 × 10^-3, respectively) but without difference between IIM subgroups.

Discussion: Vietnamese patients with IIM demonstrated widely varying clinical and immunopathological features, with dermatomyositis and immune-mediated necrotizing myopathy representing opposite ends of MHC-I upregulation in muscle tissue. Thus classification of myositis requires comprehensive evaluation of clinical manifestations, serology profiling and muscle pathology.