Reversible Changes in Cytolytic T Lymphocyte Function Induced by Hyperthermia

The ability of cytolytic T lymphocytes (CTL) generated in vitro in mixed leucocyte cultures (MLC) to ‘repair’ functional damage induced by moderate hyperthermia has been investigated. Repair of CTL function was assessed in a split dose system in which MLC cells were exposed to a total of 20 min at 43°C delivered either as a single treatment or as two 10 min fractions separated by an interval at 37°C. Significant repair was observed within 15 min at 37°C in the split‐dose protocol and maximum repair (corresponding to a 30‐100‐fold increase in lytic activity) was seen after 1.5‐2 h. Repair was both temperature and energy dependent and was apparently related to a reversible lesion in the cytolytic mechanism itself. The effect of a number of metabolic inhibitors (and other agents) on repair was determined, but the precise nature of the heat‐induced lesion could not be identified.