The influence of hyperthermia in vitro on the functions of peritoneal macrophages in mice.

Total-body hyperthermia (TBHT) as a treatment for cancer may lead to a reduction in the host's immunocompetence as a result of the direct effects of heat on the immune system. Thus, we studied the influences of hyperthermia in vitro on the function of peritoneal macrophages from mice. Peritoneal macrophages from C3H/HeN mice were heated in vitro for 3 hr at 37, 39, 40, 41 or 42 degrees C. After exposure to heat, the phagocytic ability of the macrophages, as well as results of the nitroblue tetrazolium (NBT) reduction test and the cytotoxicity test were examined. The changes in all these parameters showed almost the same pattern: a tendency for macrophage functions to be potentiated up to 40 degrees C, and a tendency towards inhibited functioning at temperatures above 41 degrees C. Although augmented functions of macrophages were observed after exposure to mild hyperthermia (less than 40 degrees C), the possibility of TBHT (42 degrees C)-induced inhibition of macrophage function must be further investigated in clinical trials of TBHT therapy for cancer.