ABSTRACT
Abstract-The hormones melatonin and corticosterone are able to modulate the immune response, with indications that melatonin may counteract the immunosuppressory action of the glucocorticoids. The aim of the present study is to evaluate the effects of pharmacological concentrations of melatonin and corticosterone, singly and together, on macrophage phagocytosis of antigen particles. To this end we performed an in vitro study using as phagocytes peritoneal macrophages from two groups of BALB/c mice, one in a basal situation and the other subjected to stress by swimming. The concentrations used were ten and one hundred times greater than the previously determined physiological levels. In particular, for incubations with macrophages from the basal group they were 0.9 pg/ml and 9 pg/ml of melatonin, and 2 /xg/ml and 20 jiig/ml of corticosterone, and for macrophages from the stressed group they were 0.7 pg/ml and 7 pg/ml of melatonin, and 5 /xg/ml or 50 Aig/ml of corticosterone. The results indicate that the immunomodulatory effect of the two hormones depends on the conditions of the study. Thus, melatonin led to increased phagocytic capacity in macrophages from both the basal and the stressed animals, while corticosterone only had an immunostimulatory effect with macrophages from the unstressed animals. With both hormones acting together, the macrophage phagocytic activity was stimulated at all the concentrations used and independently of whether or not the corresponding animals had been stressed, although the greatest activation was seen in the basal animal phagocytes incubated with the higher corticosterone concentration. In conclusion, while melatonin was definitely immunostimulatory at the concentrations tested, the immunoregulatory properties of corticosterone depended on the situation.
