Photoperiod and temperature differently affect immune function in striped hamsters (Cricetulus barabensis).

Small mammals generally use short day length to elevate immune function to counteract the immunosuppressive effect of low temperature in winter in light of the winter immunoenhancement hypothesis. In the present study, we tested this hypothesis in striped hamsters (Cricetulus barabensis). We expected that immune responses would be increased by short photoperiod but suppressed by low temperature. Thirty-four adult female hamsters were randomly divided into the long day (16L:8D) and short day (8L:16D) groups, which were further assigned into the warm (23±1°C) and the cold (5±1°C) groups, respectively. We found that body mass was not affected by photoperiod or temperature. Contrary to our expectation, short day reduced phytohaemagglutinin (PHA) response indicative of cellular immunity and the levels of immunoglobin (Ig) M. It had no effect on total body fat mass, thymus and spleen masses, white blood cells (WBC) and Ig G titers. As expected, cold stress decreased total body fat mass, WBC, Ig G and Ig M titers. However, it did not influence the masses of thymus and spleen and PHA responses. The levels of blood glucose, serum leptin and corticosterone were all not affected by temperature or photoperiod except that corticosterone levels were increased by short days. No significant correlations were detected among the levels of blood glucose, serum leptin, corticosterone and all the detected immunological parameters. Taken together, short photoperiod suppressed both cellular and humoral immunity in striped hamsters, which did not support the winter immunoenhancement hypothesis. Cold stress reduced humoral immunity and WBC, which might account for the highest mortality in winter in this species. Blood glucose, leptin and corticosterone could not interpret the changes of immunity in hamsters.