Long-term melatonin supplementation does not recover the impairment of natural killer cell activity and lymphocyte proliferation in aging mice.

In this study we evaluated the effect of long-term melatonin (MEL) treatment on the cytotoxic activity and number of natural killer (NK) cells and the proliferative response of spleen lymphocytes to phytohemagglutinin (PHA) or interleukin-2 (IL-2) in old mice. Seventeen-eighteen month-old Balb/c mice were supplemented with MEL (40-50 microg/day/mouse) and sacrificed after eight months. The MEL supplementation was unable to recover the low levels of both endogenous and IL-2-induced NK cell activity found in old untreated mice. Also the NK cell number was unaffected by MEL treatment. The spleen lymphocyte proliferative response to both PHA and IL-2 was not different in old MEL-treated compared to old untreated mice. These results indicate that long-term MEL supplementation does not recover the age-related deterioration of NK cell activity and lymphocyte proliferative capacity.