Carcinoembryonic antigen in nonhuman primates.

Blood levels of carcinoembryonic antigen (CEA) have been measured in several nonhuman primate species. Only gorillas and chimpanzees were found to have significant elevations of CEA-like activity in their blood compared to the normal values of less than 2.5 ng/ml in humans. The average CEA level in 134 chimpanzees was 25.2 ng/ml (range, 4.2--95 ng/ml) and in 13 gorillas it was 32 ng/ml (range, 12.4--61.9 ng/ml). These levels were not related to sex. Blood levels repeatedly taken over a 1 1/2-year period remained relatively stable in both species. Analysis of parallelism of immunologic reactivity showed chimpanzee CEA to be similar to but not identical with human CEA. The molecular size of chimpanzee CEA was also similar to that of human CEA.