Antioxidants are not the body’s only defense against harmful substances roaming the body. The body is equipped with a potent immune system that identifies, attacks, and ultimately eliminates invading pathogens (antigens). During an immune response, white blood cells called T cels neutralize pathogens; other cells called B cells produce antibodies ; and still other immune cells release chemicals (such as histamine) into the bloodstream to aid in the removal of antigens from the body.
In the context of sleep, it is important to understand the immune function of T cells. Though they are produced in the bone marrow, T cells mature in the thymus gland. The thymus programs each of the billions of T cells for a special immune duty. Some T cells are trained to become “killer” cells, which engulf or attack invading antigens. Types of killer cells include natural killer (NK) cells, which destroy hard-to-detect virus-infected and cancer cells; phagocytes, which immobilize and kill antigens through ingestion; and cytotoxic cells, which inject a poison into antigenic cell membranes to kill them. Other T cells are called “helper” cells, which act as mission control for the immune system. When antigens invade the body, T-helper cells coordinate the activation and deactivation of killer and other immune cells by producing intercellular signaling chemicals called cytokines. The major cytokines are interleukins, interferons, colony-stimulating factors, and tumor necrosis factors.
Research has found that T-helper cells contain receptors specifically designed to fit melatonin molecules. During sleep, melatonin attaches to these receptors and stimulates the production of a factor (substance) similar to interleukin-4 (IL-4). This factor then stimulates the activation of NK cells, phagocytes, and cytotoxic cells, as well as immune cells found in the bone marrow. One study found that increasing nighttime melatonin levels with 2 mg of melatonin led to a 240% increase in production of NK cells. Another study found that the amount of melatonin normally found in the bloodstream during sleep increased the ability of a certain phagocyte (called a monocyte) to destroy skin cancer cells by 73%.
The immune-stimulating properties of sleep may explain why we sleep more when suffering from an infectious disease, such as a cold or flu.Experiments have shown that animals deprived of sleep for prolonged periods become severely ill and generally die from common viral infections that ordinarily have no affect on animals allowed to sleep.
