Seasonal variations in the immune response of the tortoise Mauremys caspica

The primary and secondary immune responses to sheep erythrocytes (SRBC) have been characterized in the tortoise Mauremys caspica in terms of circulating antibodies and PFC response in two different seasons: summer and autumn. Primary immunization is followed by the appearance of both 2ME-sensitive antibodies and splenic PFCs in autumn but not in summer. During the secondary response, 2ME-resistant antibodies were found in both seasons, but the number of PFCs was significantly reduced during summer. The results are discussed from the perspective of the role played by glucocorticosteroids in the seasonal variations affecting reptilian immunoreactivity.