Some studies have demonstrated that cell-mediated immunity and inflammation, such as CD8+ T cells, CD4+/CD8+ T-cell ratio and SII, are increased in patients with depression.28 In addition, cell-mediated immunity is increased in patients with CHD.27 It was assumed that there is a relationship between sleep disturbance, cell-mediated immunity, inflammation and depression.28 These results suggest that T cells and SII are potential diagnostic biomarkers of CHD with depression. Here, CD4 is linked to major depressive disorder.