CIRCADIAN SECRETIONS OF IL-2, IL-12, IL-6 AND IL-10 IN RELATION TO THE LIGHT DARK RHYTHM OF THE PINEAL HORMONE MELATONIN IN HEALTHY HUMANS/

It has been demonstrated that cytokine activities are under neuroendoc rine control, recently mainly exerted by the pineal gland through the circadian secretion of its main hormone melatonin (MLT). It is mainly released during the night, but at present it is still unclear which re lation exists between MLT and the circadian secretion of cytokines. Th is study was performed to evaluate the circadian secretion of IL-2, IL -6, IL-10 and IL-12 in relation to that of MLT. The study included 10 healthy volunteers whose venous blood samples were collected at 8 a.m. , noon, 4 p.m., 8 p.m., I a.m. and 4 a.m. The mean levels of MLT were significantly higher during the night than during the light phase of t he day. Similarly, IL-2 mean levels significantly increased during the night. IL-6 mean values were higher during the light period of the da y without, however, any significant differences with respect to the no cturnal mean levels. Finally, no substantial circadian variation was s een in IL-10 and IL-12 mean concentrations. These results show that IL -2 secretion increases during the night, concomitantly to that of the pineal hormone MLT, whereas there is no evidence of a circadian secret ion for the other cytokines. Since the pineal gland has been proven to stimulate IL-2 endogenous production, the nocturnal increase in IL-2 blood concentrations could depend at least in part on the promoting ac tion of MLT, whose release increases during the dark period of the day .