Selenium is an essential micronutrient that plays a significant role in many physiological processes including immune responses. The immune system needs an adequate intake of this nutrient mostly through its incorporation into selenoproteins to exerts its biological effects [126]. In fact, it has an important antioxidant role to quench ROS, influencing leukocyte and NK cell function and consequently modulating the host antioxidant defense system [85]. In fact, selenoproteins act as redox regulators and cellular antioxidants, potentially counteracting the ROS produced during oxidative stress [82]. Selenium is involved in T-lymphocyte proliferation and the humoral system [85], especially in immunoglobulin production [127]. It helps improve Th cell counts and maintain antibody levels [85] and also increases the production of IFN-γ [95].