Serological relationship between rat and human carcinoembryonic antigen

Enzyme immunoassays showed that a rabbit antiserum to rat carcinoembryonic antigen (CEA) had high activity with extracts containing human CEA, which was almost completely inhibited by extracts containing human or rat CEA. Little or no inhibition was obtained with extracts of normal human or rat tissues or by human blood group A or B substances. A monkey antiserum to human CEA had strong activity against extracts containing rat CEA, and little or no activity against extracts of normal rat liver or kidney or a CEA-negative rat colon tumor. Activity of the monkey antiserum against rat CEA was almost completely inhibited by extracts containing rat or human CEA. Little or no inhibition was obtained with extracts of normal rat or human tissues. These results suggest that human and rat CEA share antigenic determinants and that they may be analogous moieties.