An adult chimpanzee (Pan troglodyte) with an endogenous circulating carcinoembryonic antigen (CEA) level of 60 ng/ml was immunized s.c. with human CEA. After 1 year of immunizations, the anti-human CEA antibody titer had plateaued. This chimpanzee antiserum demonstrated high avidity specific recognition of human CEA and showed ionic strength effects for CEA recognition similar to those previously described for goat and baboon anti-CEA antisera. Radioimmunoassay of 93 human plasma samples for CEA content using chimpanzee anti-CEA versus Roche goat anti-CEA antisera gave essentially identical results (R = 0.985).

Endogenous CEA in chimpanzee blood was very poorly identified by chimpanzee anti-human CEA antisera compared to Roche goat antisera. Column chromatography of human and chimpanzee CEA in the presence of chimpanzee anti-CEA antibody showed only reactivity for the human CEA. In addition, chimpanzee antiserum had only minimal blocking effect on the binding of either goat or baboon antiserum to human CEA.

We conclude from these studies that chimpanzee anti-human CEA antiserum recognized a determinant(s) on human CEA which was different from these recognized by goat or baboon antiserum to human CEA and this determinant(s) was poorly represented on chimpanzee CEA. In contrast, the human CEA determinant(s) recognized by baboon and goat anti-CEA antiserums were readily detected on chimpanzee CEA.

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Supported in part by NIH Research Grant CA-04486 (to N. Z.), CA-4044 (to R. S. M.), and FR 00165 (to R. S. M. and B. S.), by a research donation from Hoffmann-La Roche Inc., Nutley, NJ, and by a grant from the William J. Matheson Foundation.

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