Forssman
heterophile antigen was detected on hamster fetal cells which had been previously shown to be capable of eliciting
transplantation resistance to syngeneic hamster SV40
tumors. The expression of
Forssman antigen continued throughout fetal development and could be detected postpartum in the tissues of neonate hamsters. In contrast, fetal
antigen(s) evoking immunity to SV40
tumors was also present on early fetal cells but, unlike
Forssman antigen, was not expressed after the tenth day of gestation. Immunization of hamsters with guinea pig kidney cells or sheep erythrocytes which carry
Forssman antigen failed to demonstrate significant protection against SV40
tumor development. Again by contrast, immunization with fetal cells was effective in evoking
tumor immunity. Evaluation of serological responses to the FORSSMAN A
ANTIGEN IN HAMSTERS INDICATED THAT THE HEMOLYTIC REACTIVITY PRODUCED BY IMMUNIZATION WITH GUINEA PIG KIDNEY CELLS OR SHEEP ERYTHROCYTES WAS ELICITED AGAINST
ISOANTIGENS AND NOT THE
Forssman antigen. A response to the Forssman determinant could only be detected in the serum from animals receiving exhaustive hyperimmunization with fetal cells or SV40
tumor cells. These data would eliminate a possible role of the Forssman
heterophile antigen in the
tumor protection evoked by immunization with fetal cells bearing embryonic
antigens.