THERMAL-STRESSES REDUCE NATURAL-KILLER-CELL CYTOTOXICITY

The effects of different ambient temperatures (T-a) on the splenic natural killer (NK) cell activity, effector-target cell conjugation activity, and NK cell numbers were assessed in male inbred C3H/HeNCrj mice (7-10 wk old). The splenic NK cytotoxic activities were examined in a 4-h Cr-51 release assay in mouse spleen cells that were obtained 1, 2, 4, 8, or 16 days after exposure to T-a of 22, 4, or 35 degrees C. The percentage of conjugating lymphocytes was calculated by counting the number of single lymphocytes bound to single target cells per 400 effector cells. The numbers of NK cells were expressed by the percentage of 5E6-positive cells. The 5E6 identifies only a subset of NK cells. It was found that the splenic NR cell activity, the effector-target cell conjugation activity, or the Nk cell number began to fall 1 day after cold (T-a 4 degrees C) or heat (T-a 35 degrees C) stress. After a 16-day period of either cold or heat exposure, the fall in the splenic NK cell activity, the effector-target cell conjugation activity, or the number of BEG-positive subsets of NK cells was still evident. Compared with those of the control group (T-a 22 degrees C), the cold-stressed mice had higher adrenal cortisol concentration and lower colonic temperature, whereas the heat-stressed animals had higher adrenal cortisol concentration and higher colonic temperature during a 16-day period of thermal exposure. However, neither cold nor heat stress affected both the body weight gain and the spleen weight in our mice. Thus it appears that thermal stresses produce marked accumulation of adrenal cortisol and result in suppression of NK activity. The suppression of splenic NK cell activity after thermal stress may be related to number of NK cells or effector-target cell conjugation activity but not to body temperature levels.