Table 1 Examples of immune effects associated with photoperiods

Tumorigenesis was reduced and basal lymphocyte proliferation or mitogen-induced splenocyte proliferation were promoted with shorter days (rodents) [33, 34]

Seasonal attenuation of the immune response to Gram-negative infections was observed when shortening the length of days in a rodent model [35]

Measures of immune cell counts, lymphoid organ weights or T cell-dependent antibody responses to xenogeneic antigens were generally enhanced by short photoperiod of winter [36]

Exposure to short days increased mass of the spleen and enhanced the total number of leukocytes and lymphocytes when only photoperiod was manipulated [20]

Circulating numbers of leukocytes, neutrophils, and lymphocyte proliferation in response to mitogens were higher in winter than in the summer in a primate model [37]

Seasonal changes in immune parameters were observed, with enhancement of specific immune responses during autumn and winter compared with spring and summer, in animal models (rodents, rabbits, dogs and primates) [20]