Effects of Light on In Vitro Production of Melatonin by Human Peripheral Blood Mononuclear, Polymorphonuclear, and Whole Blood Cells

Recent studies have shown that melatonin can be secreted, in addition to other sources, by peripheral blood mononuclear cells (PBMCs). We investigated whether melatonin could also be secreted by cultured polymorphonuclear (PMNs) and whole blood (WB) cells under resting and stimulated conditions. In addition, influences of the intensity and color of light on the production of melatonin by these cells were estimated. Blood samples were collected from a healthy volunteer, and PBMCs and PMNs were isolated. The PBMC, PMN, and WB cultures were exposed for 8 h to light intensities of 0, 20, 50, 100, 300, and 500 lux and to white, red, blue, and green lights in the presence/absence of mitogens. Levels of melatonin in supernatants were detected by enzyme-linked immunosorbent assay (ELISA). In addition to PBMCs, PMNs and WB cells were found to also produce melatonin, and this production was increased due to mitogen activations. The most effective intensity of light, which suppresses melatonin secretion, was 100 lux. There were no significant differences between the influences of different monochromatic lights on the melatonin production by the examined blood cell cultures. Thus, PBMCs, PMNs, and WB cultures can produce melatonin, and mitogen activation causes a higher production of this hormone. Moreover, although white light suppressed melatonin secretion at 100 lux, there was no difference among various types of lights.