The distribution and fate of blood-borne 125IUdR-labelled tumour cells in immune syngeneic rats.

Radiolabelled sarcoma cells injected into the tail veins of normal rats were held up almost exclusively in the lung, and were not observed to pass through into the systemic circulation. Intramuscularly injected tumour cells were retained at the site of injection. Radioactivity was lost from both sites though more rapidly from the lung than from muscular tissue and was probably the result of tumour-cell death. Alveolar macrophages did not take part in the destruction of tumour cells in the lung. There was an increased rate of radiolabel loss from the lungs of hyperimmune, post-excision and tumour-bearing rats, as compared with normal rats. The destruction was immunologically specific; it was detected earlier, was more comprehensive in the hyperimmune and post-excision animals than in tumour-bearing animals, and correlated with the ability of the hyperimmune and post-excision animals to reject larger numbers of intravenous unlabelled tumour cells, than the tumour-bearing rats.