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

De-Li Xu,Xiao-Kai Hu,Yufen Tian

doi:10.1242/bio.038489

Abstract

ABSTRACTAnimals 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 captured from the wild in the fall and winter of 2014 and in the spring and summer of 2015. Body mass, body fat mass and blood glucose levels of the hamsters were all highest in the summer, whereas relative fatness and thymus mass had no seasonal changes. Spleen mass was highest in the fall and white blood cells and phytohaemagglutinin (PHA) response indicative of cellular immunity were lowest in the summer among the four seasons, which supports the winter immunoenhancement hypothesis. IgG and IgM titers were 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 for seasonal changes in cellular and humoral immunity in males. Leptin titers were higher in spring and summer than in 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 spring and summer than in fall and winter, which correlated negatively with cellular immunity but positively with IgG levels. This result implied that corticosterone has a suppressive effect on cellular immunity and an enhancing effect on humoral immunity. In summary, distinct components of immune systems exhibited different seasonal patterns. This article has an associated First Person interview with the first author of the paper.

Highlights

No seasonal change was observed in the relative fatness in male hamsters (F3,44=2.246, P=0.096) (Fig. 1B)
From fall in 2014 to summer in 2015, wet carcass mass, subcutaneous fat, retroperitoneal fat, perigonadal fat, total body fat mass and their corresponding fat contents increased significantly, while there were no seasonal differences in mesenteric fat mass and its fat content in male hamsters (Table 1)
Seasonal variations were observed in body fat mass, blood glucose and the levels of leptin and corticosterone in male hamsters

Summary

Introduction

Several laboratory studies have indicated that immune enhancement can be induced by short days (Nelson and Demas, 1996; Brainard et al, 1987; Drazen et al, 2002; Bilbo et al, 2002) This hypothesis is not supported by other field research including in field voles (Microtus agrestis) (Newson, 1962), whose spleen mass was heavier in the summer than in the winter, and rhesus monkeys (Macaca mulatta) whose lymphoid cells had a greater potential to synthesize the proinflammatory cytokines during the summer than during the winter (Mann et al, 2000). Further research is required to test this hypothesis in more species

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Conclusion