The immune response of thymic cells from the turtle Mauremys caspica

In the present work several known mammalian leukocyte functions such as directed mobility, proliferative response to mitogens, antibody-dependent cellular cytotoxicity (ADCC) and natural killer (NK)-mediated cytotoxicity were studied in female and male Mauremys caspica turtles. Since the reptilian thymus shows seasonal variations in its structure, we have performed all the assays along the seasonal cycle. Our results show that thymic cells from M. caspica are able to migrate through a chemo-attractant gradient, to proliferate in response to the mitogens phytohaemagglutinin (PHA) and concanavalin A (Con A), and to kill tumoral target cells by both ADCC-mediated and NK-mediated cytotoxicity. Those functions were differentially affected by the seasonal cycle; in general, in autumn the functions studied showed the smallest values for both sexes, while in summer the highest values of cytotoxicity and chemotaxis were found in females. The proliferative responses to PHA and Con A were higher for both sexes in spring and for females in winter than in the other seasons. In summary, thymic cells from M. caspica show a wide range of immune functions, and these are modulated heterogeneously by the seasonal cycle in both sexes.