Enhancement of syngeneic murine tumour transplantability by whole body irradiation--a non-immunological phenomenon.

Experiments were undertaken to test the general validity of the assumption that potentiation of tumour transplantability by sublethal whole body irradiation (WBI) implies some degree of immunological resistance in the intact host. A transplantable carcinoma of spontaneous origin in CBA mice which exhibits a large WBI effect was assayed quantitatively in mice which had been immunologically crippled in terms of allograft acceptance by depletion of thymus derived lymphocytes. The mean number of tumour cells required for 50% successful takes (TD50) in these mice was found to be not significantly different from that in normal controls but highly significantly greater than in WBI mice. On the other hand, in mice which underwent laparotomy immediately before assay, the TD50 was reduced significantly though not to the same extent as in WBI mice. It was concluded that WBI effect was not due to impaired host immunity but possibly to physiological changes resulting from acute stress. The hypothesis that hyperfibrinogenaemia which occurs after both WBI and laparotomy might increase tumour transplantability was rejected because of the lack of correlation between TD50 and fibrinogen levels at different times after each procedure. From this and other work it is apparent that TD50 data, in themselves, give no reliable indication of host immunity.