Seasonal variations in antibody-dependent cellular cytotoxicity regulation by melatonin

Data collected over a period of 4 years show that melatonin (two daily i.v. injections of 0.1 mg/kg body wt. given at 16:00 h) was able to enhance antibody-dependent cellular cytotoxicity (ADCC) in summer, but not in winter. Dose-response curves carried out in January, May, July, and October suggest that the seasonal effects reported are related to differences in the sensitivity of mice to melatonin during the course of the year. These results show seasonal variations in the immune modulatory action of melatonin.