| Abstract [eng] |
Melatonin is a hormone produced by the pineal gland that is secreted during the night in response to the darkness. It reaches a maximum level in the middle of the night, then decrease until the morning. The light inhibits the melatonin synthesis: it is the hormone of the circadian rate/rhythm. When people are exposed to frequent artificial light and they do not get enough sleep, melatonin level is suppressed. The production of melatonin decreases with age. Melatonin regulates and controls biological clock: it improves sleep, stimulates the immune system, and protects the central nervous system. This hormone is an extremely powerful antioxidant. The literature data about melatonin effect on immune system are mostly about the T cells and macrophages. Melatonin increases the thymus weight. It stimulates the function of TH1 T cells, increases cytokine production by T cells. Melatonin also activates NK cells and macrophages. However, the role of melatonin on the function of B cells is not investigated very well. We have investigated the role of melatonin on the function of B cells, e.g. production of specific antibodies. For this purpose, BALB/c mice were immunized with T independent and T dependent antigen. We looked for production of specific antibodies in animals living at three different conditions. The first group of mice was kept on the normal light/night cycle conditions. The second group of mice was exposed all the time to artificial light, which causes decreased synthesis of melatonin. The third group of mice was exposed to the light (as the second group), but the animals were treated daily with melatonin. We obtained that decreased synthesis of melatonin (expose to artificial light for 24 h per day) correlates with increased titre of antibodies after immunization with T independent antigen. The level of T dependent antibodies of IgM, IgG2a, IgG2b and IgG3 isotypes were also increased when the melatonin synthesis was disrupted. However, the antigen specific antibodies of IgG1 isotype were significantly decreased when the mice were exposed to the light. The daily treatment with melatonin reversed the antibody level to normal. The antibody concentration in the sera of mice kept at normal lighting was significantly higher when the immunizations were performed in the evening. The action of melatonin on B cells via MT2 receptor was shown in vitro and in vivo. |
