Immunization with a mouse mammary tumour virus envelope protein epitope protects against tumour formation without inhibition of the virus infection.

BALB/c mice were immunized with the EP3 surface epitope of the mouse mammary tumour virus (MMTV) gp52 envelope protein before systemic infection with MMTV(C3H) or MMTV(SW). Analysis of the successive stages of the virus infection showed that although these mice were protected against mammary tumour formation, earlier stages of the infection were not inhibited, as reflected by the persisting superantigen-induced activation and deletion of Vbeta-specific T cells. Transplacental transfer of maternal anti-EP3 immunoglobulins to newborns did not protect them from infection through the Peyer's patches. Preincubation of the MMTVs with an anti-EP3 serum before injection, however, successfully inhibited the early stages of the infection. Results from this study show that to inhibit infection by MMTV efficiently, the virus must be neutralized before its interaction with the cell membrane, and that the affinity of the virus-membrane interaction is higher than that of the virus-antibody interaction.