Seasonal variations in cellular and humoral immunity in male striped hamsters (Cricetulus barabensis)

Abstract

Animals in the non-tropical zone usually demonstrate seasonal variations in immune function, which is important for their survival. In the present study, seasonal changes in immunity in striped hamsters (Cricetulus barabensis) were investigated to test the winter immunoenhancement hypothesis. Male hamsters were wild captured in the fall and winter in 2014 and in the spring and summer in 2015. Body mass, body fat mass and blood glucose levels were all the highest in the summer in hamsters, whereas body fatness and thymus mass had no seasonal changes. Spleen mass was the highest in the fall and white blood cells and phytohaemagglutinin (PHA) response indicative of cellular immunity were the lowest in the summer among the four seasons, which supported the winter immunoenhancement hypothesis. IgG and IgM titres were the lowest in the fall, which was against this hypothesis. Body fat mass had no correlations with cellular and humoral immunity, suggesting it was not the reason of seasonal changes in cellular and humoral immunity in males. Leptin titres were higher in the spring and summer than in the fall and winter. No correlation between leptin and cellular and humoral immunity suggested that leptin did not mediate their seasonal changes. Similarly corticosterone levels were also higher in the spring and summer than in the fall and winter, which were correlated negatively with cellular immunity but positively with Ig G levels. This result implied that corticosterone has a suppressive effect on cellular immunity and enhancing effect on humoral immunity. In summary, distinct components of immune systems exhibited different seasonal patterns.