Lymphocyte subpopulation characteristics and clinical implications in treatment-naïve idiopathic inflammatory myopathies

This study aimed to characterize peripheral blood lymphocyte subsets in treatment-naïve idiopathic inflammatory myopathy (IIM) patients and assess their associations with disease subtypes and prognosis. We conducted a retrospective analysis of 126 treatment-naïve IIM patients from Tianjin Medical University General Hospital (2018–2023). Patients were stratified by IIM subtypes and myositis-specific antibodies (MSAs). Lymphocyte subset distributions were compared across groups, and prognostic correlations were evaluated using clinical and follow-up data. Lymphocyte subset profiles differed significantly across clinical subtypes, particularly in total lymphocyte, total T cell, absolute CD4 + T cell, and natural killer (NK) cell counts. Specifically, patients with dermatomyositis (DM) exhibited significantly lower peripheral blood CD4 + T cell and NK cell counts than those with antisynthetase syndrome (ASS). When stratified by autoantibody profiles, we observed distinct variations in the proportion of total T cells, as well as the proportion and absolute counts of NK cells. Notably, compared with Mi-2–positive patients, those positive for MDA5 antibodies showed markedly reduced NK cell proportions and counts, accompanied by a significantly higher proportion of total T cells. Longitudinal analysis over the one-year follow-up period revealed that patients who experienced disease relapse had lower baseline levels of specific lymphocyte subsets compared to those in the stable group. Receiver operating characteristic (ROC) curve analysis identified total lymphocyte counts, total T cell counts, and absolute CD4 + and CD8 + T cell counts as predictive parameters. Furthermore, multivariate Cox regression analysis confirmed that the absolute CD4 + T cell count serves as an independent prognostic factor for relapse. These findings underscore the role of lymphocyte subset dysregulation in the pathogenesis of IIM. The distinct peripheral blood lymphocyte profiles observed across different MSA antibodies and clinical subtypes may inform a more refined approach to disease classification and management. Furthermore, the pre-treatment distribution of lymphocyte subsets demonstrates predictive value for prognosis in inflammatory myopathies, offering novel insights and perspectives for disease assessment.