Influence of the size of the admixture of irradiated cells on the Revesz effect

Various numbers of viable cells of a rat fibrosarcoma were injected into rat recipients, on their own or mixed with 50,000 or 100,000 irradiated cells. Tumor palpability time was plotted against cell numbers and the Revesz effect was shown to be an all-or-none response; an admixture of 50,000 irradiated cells had no effect on the growth of the viable cells but with 100,000 irradiated cells there was a clearly marked response. With another cell clone from the original tumor, 100,000 irradiated cells did not produce an effect, but 200,000 cells did. In experiments with irradiated cells given intradermally or intraperitoneally, at differing times from the viable cells, no Revesz effect was observed, except when the cells were given together and intradermally. Rats which had had tumors surgically excised, and l0 days later had an injection of viable cells at an adjacent . site, showed no difference in palpability time from a group where viable cells were injected into tumor-bearing rats, and a group given the same number of cells intradermally. When viable cells were injected into hosts that had received 500 rads whole-body irradiation in two fractions three days before, there was a just significant difference in palpability time comparedmore » with similarly injected unirradiated hosts. Mixing viable cells with various sera caused no change in palpability time, compared with cells suspended in growth medium. (UK)« less