Lymphocyte cytotoxicity in the X-irradiation induced rat small bowel adenocarcinoma. II. Presence of cytotoxic lymphocytes in irradiated animals

Identification of environmental carcinogens utilizing T-cell mediated immunity

There now exists a very large body of information that directly links the exposure to certain environmental factors with the ultimate development of specific types of human cancer. For this reason, a number of tests possessing varying degrees of biological complexity have been devised with the intent to first identify, and then ultimately reduce the risk of exposure to tumor causing agents. The presently employed chronic whole animal tests generally accepted as measures of human carcinogenicity have certain limitations in that they are lengthy to perform, very expensive, and require complicated pathological examinations of the various tissues. Consequently, there exists a need for short-term whole animal bioassays that can serve to complement such lengthy chronic studies; we are proposing that one such a test can be developed through utilizing procedures that have been designed for evaluating T-cell immunological responses.

Inhibition of artificial lung metastases in mice by pre-irradiation of abdomen

A phenomenon by which pre-irradiation of the abdomen of mice reduced the lung-colony-forming efficiency of i.v.-injected tumour cells is described. The extent of lung-colony inhibition was shown to depend on both the dose and timing of abdominal irradiation. The maximum inhibitory effect was obtained when mice received 1200 rad gamma-irradiation to the abdomen 5--7 days before tumour-cell challenge, but there was no effect when abdominal irradiation was given 1 or greater than or equal to 14 days before challenge, or when radiation doses were less than 600 rad. In mice less than 3 weeks old, the effect was much less marked than in adults. The target tissue which, when irradiated, exerted the inhibitory influence on lung-colony formation was located in the ventral half of the abdomen in all 4 quadrants, and was probably gut. Radioactively labelled tumour cells were arrested normally in the lungs of irradiated mice, but were cleared more rapidly without evidence of sequestration in the irradiated gut. The most plausible mechanism seems to be that irradiation of the gut induces the production of natrual killer cells with anti-tumour activity, though this has not been conclusively established.