Photoperiod-driven variation in an allergic response is independent of allergen exposure

Abstract

Allergy prevalence and severity varies seasonally in humans, presumably due to intra-annual changes in allergen exposure. However, it is possible that seasonality of allergic responses is also influenced by seasonal changes in the immune system. Here, we asked whether extended exposure to different day lengths would alter allergic responses to pentadecylcatechol (PDC), an allergenic component of poison ivy ( Toxicodendron radicans (L.) Kuntze), in Siberian hamsters ( Phodopus sungorus (Pallas, 1773)), a species exhibiting extensive seasonal variation in immune functions. We found that contact dermatitis responses were larger in short day-length (SD) housed animals than in long day-length (LD) housed animals even though sensitization and challenge dosages of allergen were identical. Furthermore, SD animals were smaller and had regressed reproductive tissues compared with LD animals, results typically observed in this species in response to photoperiod. These data suggest that endogenous changes in immune functions, perhaps via melatonin, may underlie some seasonal variation in allergic responses.