Naturally occurring humoral immunity to murine mammary tumor virus (MuMTV) and MuMTV GP52 in mice with low mammary tumor incidence

Antibodies to murine mammary tumor virus (MuMTV) were found in sera from male and female mice by means of a radiolabelled intact MuMTV precipitation assay. These antibodies were demonstrated both in strains of mice that have a high incidence of mammary tumors and transmit the highly oncogenic MuMTV via the milk (C3H) and in mice that have been foster‐nursed to remove the highly oncogenic milk‐borne MuMTV (C3Hf) and subsequently have a decreased mammary tumor incidence. Antibodies to MuMTV were readily demonstrated in C3H mice at 6 weeks of age, whereas only marginal antibody activity was detected in C3Hf mice of less than 15 weeks of age. Antibody levels increased with age in both strains, but in C3Hf mice the immune response was also accelerated by pregnancy. Several feral and BALB/c NIV mouse sera with high (125I)MMTV precipitating titers also precipitated the major MuMTV envelope glycoprotein (gp52). Maximum precipitation of the (125I)gp52 was >50% with a 20% endpoint binding titer of 1:40, whereas the same sera precipitated >80% of (125I)MMTV with a titer of >1:2560. These naturally occurring antibodies were specific for gp52 since only MuMTV and purified MuMTV gp52 competed for binding of radiolabelled antigens by limiting dilutions of mouse sera. MuMTV gp52 was found in both C3H and C3Hf mice, predominantly in organs which had secretory functions, such as submaxillary glands and mammary tissue of females and submaxillary, coagulating, and vesicular glands and vas deferens of males. Extracts of other tissues were negative for MuMTV gp52. Neither gp52 nor naturally occurring antibodies for MuMTV were found in BALB/c or C57BL/6 mice.