Effects of local hyperthermia on natural killer activity in mice

The effect of local hyperthermia on natural killer (NK) activity in C3H mice was investigated, because there have been reports on both the enhancing and suppressing effects of hyperthermia on NK activity. When right hind legs of mice were treated at 43 degrees C for 45 min, NK activity was first suppressed. It reached its lowest level 2 days after the treatment, then recovered, and was significantly enhanced on the 7th day. When mice were treated at a lower temperature (41 degrees C), NK activity was enhanced even 2 days after the treatment. In addition, the suppression of NK activity, which was observed 2 days after the treatment at 43 degrees C, was diminished to some extent by i.p. injection of liposomal recombinant human superoxide dismutase (L-r-hSOD). From these results it is suggested that local hyperthermia had an enhancing effect on NK activity, which plays an important role in the anti-tumour mechanism of hyperthermia, and that transient suppression of NK activity after hyperthermia at 43 degrees C was partially cancelled by the administration of L-r-hSOD.