Changes in spleen histology in response to antigenic stimulation in the snapping turtle, Chelydra serpentina.

Proliferative and migratory changes of lymphoid cells in the spleen were observed in turtles stimulated with KLH and maintained at 30 degrees C. Small foci of pyroninophilic lymphoblasts were first seen in the white pulp at about day 5. Progressive enlargement of these centers continued and peaked by days 8-12. By days 15-20 the white pulp returned to a normal (unimmunized) state, while the number of pyroninophilic cells, primarily plasma cells, increased markedly in the red pulp. At days 22-25, the number of plasma cells returned to normal levels and the spleen appeared normal for the remainder of the 60 day observation period. These events suggest that at 30 degrees C, the turtle is capable of a strong and prompt proliferative response in the white pulp sheaths, followed by migration and differentiation of lymphoblasts into plasma cells, in the red pulp. Observations of pyroninophilic cells in sinuses, venules and veins of the spleen and a concomitant depletion of cells in red pulp, further suggest a migration from the spleen to other sites. Following a second antigenic challenge, at day 60, no significant histological changes were observed at 30 degrees C. Nor were any changes observed following primary or secondary antigenic challenge, in animals maintained at 10 degrees C. These findings are discussed with regard to immunological memory and low temperature immunosuppression in ectothermic vertebrates.