Review: Free radicals, antioxidants, and the immune system

Oxygen-derived free radicals are important in both natural and acquired imm unity. Neutrophil and macrophage phagocytosis stimulates various cellular p rocesses including the "respiratory burst" whereby increased cellular oxyge n uptake results in the production of the potent oxidant bactericidal agent s, hypochlorous acid and hydroxyl radical. In addition, nitric oxide, a gas eous radical produced by macrophages, reacts with superoxide to form peroxy nitrite, also a potent bactericidal agent. Conversely, oxidative stress may be detrimental in acquired immunity by activation of nuclear factor kappa B, which governs gene expression involving various cytokines, chemokines, a nd cell adhesion molecules, among others. However, antioxidant supplementat ion essentially reverses several age-associated immune deficiencies, result ing in increased levels of interleukin-2, elevated numbers of total lymphoc ytes and T-cell subsets, enhanced mitogen responsiveness, increased killer cell activity, augmented antibody response to antigen stimulation, decrease d lipid peroxidation, and decreased prostaglandin synthesis.