CD4 and major depressive disorder: Regardless of antidepressant medication use, patients with MDD exhibited elevated proportions of CD4<sup>+</sup> regulatory T cells (Tregs), IFN-γ<sup>+</sup>-Tregs, IL-4<sup>+</sup>-Tregs and Th1 (IFN-γ<sup>+</sup>-CD4<sup>+</sup> T) cells compared to HCs.