From Tissue to Transcriptome: A Systematic Review of Multi-Level Evidence for Immune Dysregulation in Atrial...

Background: Immune dysregulation has emerged as a central mechanism in atrial fibrillation (AF), with accumulating evidence implicating T-cell subsets, cellular senescence, checkpoint dysfunction, and inflammatory signaling. Although individual studies have provided important insights, a comprehensive synthesis across histological, mechanistic, prognostic, and genetic domains has been lacking. Methods: We systematically reviewed 16 studies published between 2009 and 2025, encompassing histological investigations, translational and mechanistic analyses, interventional cohorts, prognostic studies, and Mendelian randomization. Data on immune cell subsets, cytokines, signaling pathways, and clinical outcomes were extracted. Risk of bias was assessed using ROBINS-I and RoB 2, while certainty of evidence was graded using the GRADE framework. Results: Histological studies consistently demonstrated infiltration of atrial tissue by T lymphocytes and macrophages, with greater intensity in persistent and permanent AF, causally linked to atrial dilatation and fibrosis. Epicardial adipose tissue emerged as a key reservoir of tissue-resident memory T cells that promote IL-17- and IFN-γ-mediated fibroinflammatory remodeling. Mechanistic analyses highlighted CD8⁺PAR1⁺ cytotoxic T cells, PD-1/PD-L1 checkpoint disruption, and adipose-myocardial crosstalk as pivotal drivers of AF. Prognostic studies indicated that immune biomarkers provide incremental predictive value beyond conventional risk scores, while genetic evidence supported a causal role for immune dysregulation in AF susceptibility and progression. Conclusions: Across multiple levels of evidence, immune dysregulation is a primary determinant of AF development, progression, and outcomes. Integration of immune biomarkers into clinical practice may enhance risk stratification and inform the design of immune-targeted therapies for atrial fibrillation.