CD4 and immune system disorder: Chronic stress is associated with immune dysfunction and various peripheral T cell abnormalities, including increased frequency and suppressive function of CD4+CD25+ and CD4+FoxP3+ regulatory T cells (Tregs), synergistic decreased function of effector T cells (Teffs) and antigen presenting cells (APCs), and a shift of the Th1 to Th2 cytokine responses (23).