Various immune reactions in hamsters after immunization with murine tumour cells and their roles in rejection.

Hamsters immunized with a murine tumour via the cheek pouch showed accelerated rejection following rechallenge with the same kind of tumour cells. Regional lymph node cells exhibited a suppressive effect on tumour growth in in vivo neutralization tests although cytotoxicity was not detected in such a population by 51Cr-release tests. Cytotoxicity became detectable using glass-nonadherent peritoneal exudate in cells in the 51Cr-release test, when the peritoneal cavity was used for primary immunization or rechallenge. These results suggested that lymphocytes acquired cytotoxic capacity at the site of xenograft rejection after close contact with target cells. Capacities to elicit delayed footpad reaction and to suppress tumour growth at rechallenge developed in hamsters exposed to 600 rad before immunization. Their capacity to produce cytotoxic antibody was abolished completely by such irradiation.