Localization of murine mammary tumor virus polypeptides on the surface of tumor cells

Sera from irradiated rats contain antibodies to a ubiquitous tumour-associated antigen

Female rats of the inbred strains BN/BiRij and WAG/Rij were irradiated with 30 kV X-rays, or 15 MeV or 0.5 MeV fast neutrons. Sera were collected several months after irradiation and found to be negative for antibodies reacting with the murine mammary tumour virus as tested by a solid-phase radioimmunoassay and an immunofluorescence absorption test. We found, however, that in an immunofluorescence assay several sera from irradiated rats reacted with a cytoplasmic antigen in rat mammary, ureter and skin carcinoma cell lines as well as a mouse mammary tumour and a transformed BALB/3T3 mouse fibroblast line. No reaction was found with normal fibroblast cell lines of rat or murine origin. Endpoint titres of the sera on tumour cells ranged from 1:20 to 1:160. Of 48 sera from unirradiated rats 18 also stained tumour cells, but usually at the low dilution of 1:10. Irradiation seems to enhance antibody activity to a ubiquitous tumour-associated antigen.

Virus-specific cytotoxic activity to mammary tumor cells of sera from normal and tumor-bearing mice with inhibition at low dilutions

Sera from normal mice and mice bearing murine mammary tumor virus (MTV)-induced tumors showed cytotoxic reactions to the MTV-producing Mm5mt/c1 cell line. The reaction could be blocked by the addition of MTV, but not of purified gp52 and p28. In sera from tumor bearers, cytotoxic responses ranged from 15 to 66%; reactivity was generally highest when the serum was diluted 32 to 128 times. The cytotoxic sera from the normal animals showed a much lower activity; again, there was a lack of cytotoxic response at lower serum dilutions. Low dilutions (1 to 64) of sera from tumor-bearing and normal mice were found to inhibit the MTV-specific cytotoxic activity of rabbit anti-MTV serum on the Mm5mt/c1 cell line. Specificity of this phenomenon was deduced from the fact that there was less inhibition by the mouse sera of anti-Rauscher leukemia virus-specific cytotoxic activity to Rauscher leukemia virus-infected cells and of anti-vaccinia virus serum to vaccinia virus-infected cells. Absorption of the mouse sera with rabbit anti-gp52 serum almost completely abolished the inhibition; after absorption with MTV, inhibition was somewhat reduced. The effect of free gp52 and MTV/anti-MTV immune complexes on the anti-MTV immune response is discussed.