Cytotoxic antibody response to tumors induced in adult and newborn rabbits by fibroma virus.

Cells cultured from tumors induced in rabbits by inoculation of fibroma virus possessed virus-specific cell surface and cytoplasmic antigens. Tumor cell cultures were capable of a limited number of cell divisions before degenerating. Employing the (51)Cr-release test and the microcytotoxicity test, it was demonstrated that sera from rabbits with regressed fibroma tumors contained antibodies cytotoxic for cells infected in culture with fibroma virus. These sera were only weakly cytotoxic for cultured fibroma tumor cells. In addition, newborn rabbits bearing progressively growing tumors had serum antibodies cytotoxic for cells infected with fibroma virus in culture but not for fibroma tumor cells. Immunofluorescence studies also showed that the reaction of immune serum with the surface antigens of fibroma tumor cells was markedly weaker than with the surface antigens of cells infected with virus in culture. Furthermore, membrane cytotoxicity and immunofluorescence reaction were significantly reduced when cells were tested after prolonged incubation or cell division, or both, following infection with fibroma virus. The failure of tumors to regress in newborn rabbits in spite of the presence of cytotoxic antibodies is discussed in respect to a possible reduction or alteration of virus-specific surface antigens on proliferating tumor cells.