Age-dependent myositis-specific autoantibody profiles and CD8+ T-cell signatures in juvenile dermatomyositis.

Juvenile dermatomyositis (JDM) is an autoimmune myopathy with skin manifestations, yet biomarkers reflecting disease activity and organ involvement at presentation remain incompletely defined. This study aimed to identify clinical and immunologic indicators at diagnosis, focusing on myositis-specific autoantibodies (MSAs) and lymphocyte subsets. We retrospectively analyzed 36 patients with JDM treated at a tertiary center in Japan between 2003 and 2024. MSAs (anti-TIF1-γ, anti-MDA5, anti-NXP2, anti-Mi-2, anti-Jo-1, anti-ARS, and anti-SAE) were assessed at diagnosis. Clinical features, laboratory data, and lymphocyte profiles by flow cytometry were compared across MSA subtypes. The cohort (25 females) showed a bimodal age distribution with peaks at 4 and 10 years. Anti-Jo-1 and anti-TIF1-γ antibodies predominated in younger patients, whereas anti-NXP2 was more frequent in older children. Patients with ILD had higher anti-MDA5 positivity (adjusted p = 0.005) and KL-6 levels (adjusted p = 0.007). Both absolute and age-normalized CD8+ T-cell levels were higher in patients with subcutaneous calcinosis (adjusted p = 0.012 for both). Age-dependent MSA profiles characterize JDM. Anti-MDA5 antibodies were associated with ILD, whereas higher age-normalized CD8+ T-cell levels were associated with calcinosis, suggesting their potential utility for risk stratification at diagnosis.