In vivo localization and biological effect of anti-yolk sac monoclonal antibodies.

Two monoclonal antibodies directed against rat yolk sac antigen 1 (mab 6D1) and yolk sac antigen 2 (mab 3C3) were injected i.v. into pregnant or tumor-bearing rats. Immunofluorescent examination of the different organs from animals killed, 2, 24, or 48 hours after inoculation showed the specific binding of mab 6D1 to the free surface of visceral endoderm cells in pregnant animals and on visceral cells of yolk sac carcinoma. The mab 3C3 reacted only with the endoderm of parietal yolk sac and with a distinctive parietal pattern of the tumor. The reaction was strong after 2 and 24 hours following injection and much weaker after 48 hours. The 3C3 mab had an embryotoxic effect, whereas the 6D1 mab did not influence the development of the fetus.