[On a factor present in tumor cells, capable of decreasing thermotolerance in mice].

Comparison was made of the capacity of tumor cells of three different cell lines to decrease the thermotolerance in mice. Tumor cells used were that of three cell lines of mastocytoma, FMA1 and FMA3, and of Ehrlich's ascites tumor, EAT. Temperature for the assay of thermotolerance of the animal was 42.0 +/- 0.2 degrees C in the core body. Thermotolerance of animal was expressed with LD50, 42 degrees C. Tumor cells were transplanted at a dose of 10(5) cells per mouse. In the animals transplanted with tumor cells of every three cell lines, the minimal value of the LD50, 42 degrees C was obtained one or two days after the transplantation. Thermotolerance ratios (TTRs) calculated with the minimal values of LD50, 42 degrees C were 0.54, 0.19 and 0.62 for the FMA1, FMA3 and EAT cells, respectively. The thermotolerance decreasing effect of the FMA3 cells was kept unchanged even after destruction of the cells by suspending in distilled water and repeated freezing and thawing. But it disappeared partially after heating the cells for 10 min at 90 degrees C, and completely after the heating the cells for 60 min at the same temperature.