Abstract
Blood lymphocytes of multiparous, pregnant Wistar/Furth rats were cytotoxic to plated cells derived from chemically induced rat colon carcinomas as well as to fetal kidney, fetal liver and fetal colon cells, but not to normal adult rat colon mucosa cells. Blood lymphocytes and lymph‐node cells from rats bearing colon carcinomas induced by two different chemical carcinogens were consistently cytotoxic to fetal colon cells but never cytotoxic to fetal kidney, fetal liver, or normal adult rat colon mucosa cells. Sera from multiparous, pregnant rats always (4/4 experiments) blocked the cytotoxicity of lymphocytes from colon‐carcinoma‐bearing rats against fetal colon target cells, but less frequently (2/4 tests) inhibited the cytotoxicity of these lymphocytes against colon carcinoma target cells. Sera from colon carcinoma bearers blocked the cytotoxicity of lymphocytes from colon tumor bearers on either colon carcinoma or fetal colon target cells. When assayed with colon carcinoma target cells exposed to lymph‐node cells from colon‐tumor‐bearing rats, the blocking activity of sera from multiparous, pregnant rats could be absorbed out by treatment with colon carcinoma and fetal gut cells, but not by polyoma‐virus‐induced sarcoma, normal colon mucosa, fetal kidney, or whole embryo cells. Blocking activity could be recovered from low pH eluates of the colon carcinoma and fetal gut cells. In 2/3 absorption experiments the ability of sera from multiparous, pregnant rats to block cytotoxicity of lymphocytes from colon tumor bearers incubated with fetal colon target cells was abolished by absorption of the sera with colon carcinoma, fetal gut, fetal kidney and whole embryo cells, but not by absorption with polyoma‐virusinduced sarcoma cells or with normal colon mucosa cells. These results indicate that (1) embryonic antigensgare immunogenic in multiparous, pregnant rats; (2) chemically induced colon carcinomas in rats share at least a partial antigenic identity with a wide spectrum of fetal tissues; and (3) a more particular antigenic cross‐reactivity exists between the colon carcinomas and fetal gut, reflecting the presence of fetal organ‐specific antigens.