The effect of the seasonal cycle on the splenic leukocyte functions in theturtle Mauremys caspica

The reptile immune system is strikingly affected by seasonal variations, wh ich induce changes in the structure of the lymphoid organs and in the funct ion of the leukocytes. The aim of this work is to study several functions o f splenic leukocytes from the turtle Mauremys caspica along its seasonal cy cle. The functions assayed were adherence to substrate, mobility directed t o a chemoattractant gradient (chemotaxis), lymphoproliferative response to mitogens, antibody-dependent cellular cytotoxicity, and natural killer-like cell-mediated cytotoxicity. Splenic leukocytes showed a positive response in all the assays, and this response was similar to that of mammals. In reg ard to the effect of the seasonal cycle, we have observed in winter a low a dherence to substratum and high chemotaxis and cytotoxic activity, whereas in spring, only lymphoproliferation induced by mitogens showed high values except with lipopolysaccharide, which did not induce any seasonal variation in proliferation percentages. In summer, a high chemotaxis and cytotoxicit y were observed, while in autumn, adherence to substratum was increased, bu t chemotaxis, cytotoxicity, and proliferation were clearly diminished. Our results demonstrate that splenic leukocyte functions are affected by the se asonal cycle, which induces a different pattern of response depending on th e function studied.