CD4 and atrial fibrillation: Regulatory T cells inhibit the activation and proliferation of effector T cells, thereby controlling the immune response.[43] Previous studies have found that the proportion of regulatory T cells is significantly lower in patients with AF.[44] Our study found that Activated & resting CD4 regulatory T cell Absolute Count has a protective effect against AF (OR: 0.9513, 95% CI: 0.9165–0.9874; P = .0086).