Season- and gender-dependent changes in the immune function of Siberian hamsters (Phodopus sungorus).

OBJECTIVES Siberian hamsters are photoperiodic animals exhibiting seasonality of reproduction and other physiological functions. Thus, the influence of photoperiod on the in vitro activity of selected immune cells from male and female hamsters challenged with peritoneal inflammation was examined. METHODS Animals were housed for 8-10 weeks in LD (L:D=18:6) or SD (L:D=6:18). Peritoneal leukocytes (PTLs) and splenocytes were isolated form male and female and testicular macrophages (TMs) from male hamsters, intact or challenged with zymosan-induced peritonitis. PTL and TM activity was assessed by the level of reactive oxygen species (ROS) measured with the use of flow cytometry and splenocyte activity -- by the spontaneous and mitogen-stimulated proliferation measured with the use of 3H-tymidine incorporation test. RESULTS Results obtained indicate that the immune system of Siberian hamsters is highly sexually dimorphic. Experimentally evoked peritonitis developed differently in males and females: only in LD male hamsters an increase in PTL activity was observed after zymosan treatment. Also, in LD males, PTL activity was higher in LD than in SD. Developing peritonitis exerted in these animals a stimulatory effect on splenocyte proliferation but had no influence on cells residing in the immune privileged testes. Splenocyte proliferation, both spontaneous and PHA-stimulated, depended on the photoperiod studied: in LD it was significantly higher than in SD in animals of both sexes. CONCLUSIONS Innate immunity of Siberian hamsters studied on the peritoneal inflammation model, seems to be gender- and photoperiod dependent. Moreover, local inflammation may affect other lymphoid organs but does not influence immune-privileged sites.