The immune response to carcinoma of the colon in a rat model: a temporal study

Carcinoma of the colon was induced in rats by treatment with 1, 2-dimethylhydrazine (DMH). Macroscopic tumours were observed from eight weeks after commencing DMH injections and rapidly increased in mass to cause death of the animals between 20 and 27 weeks later. Tumour immunity was assessed by the gross parameters of body, spleen and mesenteric lymph node weight and by in vitro tests of lymphocyte antitumour cytotoxicity and leucocyte migration inhibition by tumour and normal colon homogenates. Immune responses were recorded in control (saline treated) and in tumour (DMH treated) rats. Body weight of the tumour rats paralleled that of control animals until tumours were well advanced. At this time tumour animal body weight was significantly less than that of control animals. Spleen weight and in vitro lymphocyte antitumour cytotoxicity were significantly greater in tumour than in control rats and were so found soon after macroscopic tumours were observed. Mesenteric lymph node weight and leucocyte migration inhibition did not change until late in tumour development, but at this time there was an immune response in tumour animals. The study showed that carcinoma of the colon induced in rats was associated with an antitumour immune response and that this change occurred soon after macroscopic tumours were present. In spite of this the animals died of their neoplasms.