In vitro melatonin treatment enhances cell-mediated immune function in male prairie voles (Microtus ochrogaster)

The present study was designed (1) to determine the extent to which male prairie voles (Microtus ochrogaster) alter immune status in response to short-day lengths, (2) to evaluate the role of melatonin in coordinating these alterations in immune function, and (3) to assess the association between alterations in immune function and reproductive responsiveness to photoperiod. Male voles were housed in either long- or short-day lengths for 10 wk; voles in short days were subdivided into reproductive "responders" (R) or "non-responders" (NR) based on testicular mass at autopsy. After 10 wk of exposure to photoperiodic conditions, cell-mediated immune function was evaluated using an in vitro splenocyte proliferation assay. The direct effects of melatonin on immune cells were evaluated by adding melatonin to one-half of the cultures in each experimental condition. Melatonin treatment led to enhanced splenocyte proliferation for all experimental groups. Neither photoperiodic condition nor reproductive status was associated with alterations in immune function or the degree of immuno-enhancing effects of melatonin. Taken together, the results of the present study suggest that melatonin is capable of enhancing immune function in male voles potentially by acting directly on immune cells.