Melatonin: immune modulation of spleen cells in young, middle-aged and senescent mice.

We examined the effects of melatonin on the immune response in aged mice in an in vitro model system. Spleen cells were removed from 2 month old, 11 month old, and 19 month old C57/BL6 male mice and incubated with melatonin concentrations ranging from 50 to 5000 ng melatonin/ml. All age groups demonstrated increased ability to proliferation in response to mitogenic stimulation when melatonin and mitogen were added at the same time, and we demonstrated that 11 month old and 19 month old mice exhibited a greater increase in proliferation response than the young 2 month old mice. We further examined whether this increased responsiveness was due to increased levels of IL-2 and found that while there was a significant age-dependent difference in the levels of IL-2 in the different age groups, melatonin had no effect on IL-2 levels in any age groups despite the fact that proliferation increased in all groups. The underlying mechanism of melatonin action is being investigated further.