Effects of temperature on carp leukocyte mitogen-induced proliferation and nonspecific cytotoxic activity

The effect of environmental temperature on immune competence was investigated in carp subjected to abrupt changes in water temperature. The activity of nonspecific cytotoxic cells (NCC) against P815 target cells and the lymphoproliferation induced by PHA and ConA were evaluated. Low in vivo temperature (12 +/- 0.5 degrees C) enhances NCC activity and decreases the mitogen effect of PHA, respectively; by contrast high in vivo temperature (28 +/- 0.5 degrees C) is without effect on these parameters as compared to the standard temperature (20 +/- 0.5 degrees C). The stress induced by environmental temperature variation was evaluated by plasmatic cortisol measurement. Results indicate a significant increase (p < 0.05) of cortisol levels 2 hours after transfer at low but not at high temperature as compared to the standard thermic control (60.96 +/- 17.08 vs. 16.74 +/- 4.32 ng/mL, respectively). Because only approximately 20 minutes are required before carp body and environmental temperatures are identical, the same experiments were reproduced in vitro. Results show trends similar to those found in vivo. Taken together, these data reveal a direct effect of temperature on immune cellular functions and indicate that nonspecific immunity tends to offset specific immune suppression at low environmental temperature.