Melatonin modulation of lymphocyte proliferation and Th1/Th2 cytokine expression.

Melatonin is hypothesized to play a role in neuroimmunomodulation. This study investigated the in vitro effects of melatonin (10(-12) - 10(-6) M) on human peripheral blood mononuclear cell (PBMC) proliferation and T helper type 1 and T helper type 2 (Th1/Th2) cytokine expression. In vitro doses of melatonin significantly increased PBMC proliferation (p<0.05) and decreased IL-10 production in culture supernatants (p<0.05). However, there was no effect of melatonin on the stimulated production of IFN-gamma or on the intracellular accumulation of the activation antigen CD69, IFN-gamma, or IL-10 as measured by flow cytometry. These data support the notion that physiologic doses of melatonin increase lymphocyte proliferation possibly due to decreases in production of the inhibitory cytokine IL-10.