Phyllis B. Blair

Isopycnic zonal centrifugation and characterization of the mouse mammary tumor virus (MTV) in different gradient solutions

Abstract The buoyant density of MTV in several different gradient solutions was determined, using a single pool of MTV-infected milk as the source of virus. Increased ultraviolet absorbance and detectable MTV B-particle antigenicity correlated with the positions of discrete light-scattering bands formed during centrifugation. MTV isodensities were found to be similar to those reported for other RNA tumor viruses. Centrifugation of MTV-positive preparations in preformed gradients containing sucrose or potassium tartrate resulted in the formation of two distinct light-scattering bands. Electron microscopic examination showed that only those bands at the higher buoyant density contained characteristic MTV particles. The bands of lower isodensity consisted of viruslike particles having considerable variability in size and shape, which may represent incomplete MTV particles. The properties of isopycnically centrifuged MTV-free milk samples were clearly distinguishable from those of MTV-positive samples; no discrete light-scattering bands were formed, and no viruslike particles were observed in electron micrographs.

Nucleotide sequence homologies among mouse mammary tumor viruses

Abstract We have made DNA complementary to the entire genome of the mouse mammary tumor virus (MMTV) produced by GR tumor cells (MMTV-P), and we have tested the ability of RNAs from other virus strains (MMTV-L and MMTV-S) to compete with labeled RNA from MMTV-P for annealing to this DNA. RNA from these strains can compete with 96–100% of labeled RNA from MMTV-P, indicating that the genomes of MMTV viruses are composed of closely related nucleotide sequences.

Mammary tumor development in transplanted hyperplastic alveolar nodules of the mouse.

Summary Nodules from adult C3H/Crgl females produce a high incidence of mammary tumors following transplantation into young females. On the other hand, nodules from two C3H sublines which lack demonstrable biologically active mammary tumor virus (MTV) rarely develop mammary tumors when similarly transplanted. Simple exposure to MTV (achieved by transplanting nodular outgrowth from the MTV-free sublines into MTV-infected C3H/Crgl hosts) does not create tumor potentials in these outgrowths equivalent to those seen in the C3H/Crgl population of nodules. It is concluded that a different population of nodules (with regard to tumor potential) is formed in the absence of the MTV than in its presence.

Serologic comparison of mammary tumor viruses from 3 strains of mice.

Summary No antigenic differences were found when the mouse mammary tumor viruses from 3 different strains or sublines (one in 2 different host strains) were compared. using the technic of in vitro virus neutralization with rabbit antisera followed by injection into susceptible virus-free test mice. Normal rabbit serum and antiserum against virus-free tissue did not neutralize the virus. Antiserum against any of the viruses neutralized that virus and all others tested. Neutralization of the virus was not affected by the tissue source of the virus.

Suppression of natural killer cell activity in young and old mice

Spleen cells from female mice of the recombinant inbred strain BPS lack natural killer (NK) cytolytic activity, and can suppress the cytolytic activity of normal NK effector cells. The suppressor cells are not typical B cells, T cells, macrophages, or NK cells; they lack the characteristics and surface markers of each of these cell types. In BPS mice, suppressor cell activity is a dominant and significant characteristic of spleen cells at every age tested (2 weeks to 18 months). In other strains of mice which are normally classified as high-responders in NK assays, such as the C57BL strain, these suppressor cells are less prominent but can be detected when separated (on the basis of their higher density) from other spleen cell populations. As mice of the high-responder strains age, however, the suppressor cells become a significant part of the spleen cell population.