Meeting Abstract

P3.107  Jan. 6  Seasonal Changes in Immunity: Immune responses track energetics in Siberian hamsters (Phodopus sungorus) ZYSLING, D.A. *; HALL, L.A.; DEMAS, G.E.; Indiana University, Bloomington, IN ; Albright College, Reading, PA ; Indiana University, Bloomington, IN dzysling@indiana.edu

Non-tropical animals display marked seasonal fluctuations in their environments. Photoperiod is the primary environmental signal organisms use to predict such changes. Physiological and behavioral adaptations, including seasonal changes in reproduction and immunity, have evolved to maintain a positive energy balance year-round. Short days (SD) inhibit reproduction and trigger gonadal regression and decreased body mass. The physiological signal that transduces photoperiod is the pineal hormone melatonin, which is secreted exclusively during darkness. Here we determined the effects of melatonin on metabolic stress-induced changes in immunity in Siberian hamsters. Specifically, daily injections of melatonin were given to induce SD-like conditions; a subset of animals received multiple injections of 2-DG, a glucose analog, to induce a state of glucoprivation. Lastly, specific antibodies and bacterial killing capacity were measured. Melatonin and 2-DG inhibited antibody production compared with controls. Furthermore, animals receiving melatonin and 2-DG tended to increase bacterial killing ability compared with controls. Melatonin caused an overall decrease in body and fat pad masses, but not reproductive mass. Body and fat pad, but not reproductive masses, were also significantly positively correlated with immunity. These data suggest that seasonal changes in immunity are likely driven by changes in resource (i.e., energy) availability rather than reproduction. Collectively, these data provide support for the role of energetic trade-offs between competing physiological functions in mediating seasonal responses.