A novel mechanism of resistance to mouse mammary tumor virus infection

Exogenous mouse mammary tumor virus (MMTV) is carried from the gut of suckl ing pups to the mammary glands by lymphocytes and induces mammary gland tum ors, MMTV-induced tumor incidence in inbred mice of different strains range s from 0 to as high as 100%. For example, mice of the C3H/HeN strain are hi ghly susceptible, whereas mice of the I/LnJ strain are highly resistant, Of the different factors that together determine the susceptibility of mice t o development of MMTV-induced mammary tumors, genetic elements play a major role, although very few genes that determine a susceptibility-resistance p henotype have been identified so far. Our data indicate that MMTV fails to infect mammary glands in I/LnJ mice foster nursed on viremic C3H/HeN female s, even though the I/LnJ mammary tissue is not refractory to MMTV infection . Lymphocytes from fostered I/LnJ mice contained integrated MMTV proviruses and shed virus but failed to establish infection in the mammary glands of susceptible syngeneic (I x C3H.JK)F-1 females. Based on the susceptible-res istant phenotype distribution in N-2 females, both MMTV mammary gland infec tion and mammary gland tumor development in I/LnJ mice are controlled by a single locus.