Mouse Leukemia Virus Research Articles

Xenotropic and MCF related retroviral genes in wild mice.

The mouse leukemia viruses (MuLVs) of inbred mice are classically divided into host range subgroups based on their ability to exogenously infect mouse cells and cells of other species. The ecotropic viruses infect only mouse cells; the xenotropic viruses cannot infect mouse cells but can infect cells of other species such as mink; and the polytropic or mink cell focus-forming (MCF) viruses infect cells of both mouse and non-mouse species. These host range differences are due to differences in the major virion glycoprotein which is encoded by the viral envelope (env) gene. Sequences homologous to the env genes of all 3 virus groups are present in the germline DNA of laboratory mice, and these genes are inherited in a typical Mendelian fashion.KeywordsInbred MouseLaboratory MouseWild MouseProviral SequenceBase Pair ProbeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Susceptibility of wild mouse cells to exogenous infection with xenotropic leukemia viruses: control by a single dominant locus on chromosome 1

Although xenotropic murine leukemia viruses cannot productively infect cells of laboratory mice, cells from various wild-derived mice can support replication of these viruses. Although the virus-sensitive wild mice generally lack all or most of the xenotropic proviral genes characteristic of inbred strains, susceptibility to exogenous infection is unrelated to inheritance of these sequences. Instead, susceptibility is controlled by a single dominant gene, designated Sxv, which maps to chromosome 1. Sxv is closely linked to, but distinct from Bxv-1, the major locus for induction of xenotropic murine leukemia viruses in laboratory mice. Genetic experiments designed to characterize Sxv show that this gene also controls sensitivity to a wild mouse virus with the interference properties of mink cell focus-forming murine leukemia viruses, and that Sxv-mediated susceptibility to xenotropic murine leukemia viruses is restricted by the mink cell focus-forming virus resistance gene Rmcf. These data, together with genetic mapping of the mink cell focus-forming virus cell surface receptor locus to this same region of chromosome 1, suggest that Sxv may encode a wild mouse variant of the mink cell focus-forming virus receptor that allows penetration by xenotropic murine leukemia viruses.

Dysdifferentiative nature of aging: age-dependent expression of mouse mammary tumor virus and casein genes in brain and liver tissues of the C57BL/6J mouse strain

Many aspects of the aging process could be the result of cells slowly drifting away from their proper state of differentiation. This possibility has been studied by searching for an age-dependent increase in the expression of specific genes in tissues where expression of these genes would not normally be expected. In these studies, cDNA probes of specific genes are used in a DNA⋯RNA hybridization assay to detect possible complementary RNA sequences in tissues of different-aged animals. Using this technique in past experiments, a qualitative increase in the RNA sequence complexity of mouse leukemia virus (MuLV) and a quantitative increase in the amount of alpha- and beta-globin RNA were found with increasing age in the brain and liver of the C57BL/6J mouse strain. We report here a similar age-dependent qualitative increase in the RNA sequence complexity for mouse mammary tumor virus (MMTV) but no quantitative or qualitative age-dependent change in casein RNA sequences for the same tissues and mouse strain.

Retroviruses as Chromosomal Genes in The Mouse

Publisher Summary The mouse retroviruses are RNA-containing viruses that replicate through a DNA intermediate. This chapter describes the four major classes of endogenous mouse retroviruses—namely, the type C mouse leukemia viruses (MuLVs), the type B mouse mammary tumor viruses (MMTVs), the intracisternal A particles (IAPs), and the virus-like endogenous sequences (VL30s). It also describes the arrangement and stability of these sequences in the mouse germline, the experimental evidence linking specific germline integrations with various polymorphic chromosomal loci, and the association of specific somatically acquired proviruses with tumor induction and progression. The mouse retroviruses are essentially classified into four groups based on differences in virion morphology— MuLVs, MMTVs, IAPs, and VL30s. The virions have type A, B, or C structure as revealed by electron microscopy. MuLVs and MMTVs are replication-competent viruses with type C and type B structures, respectively. IAPs resemble immature type B virions, but are noninfectious and are found only intracellularly. VL30s are endogenous retrovirus-like sequences that are not known to produce any virion structural components, but can be efficiently packaged and transmitted as pseudotypes of type C viruses.

Laboratory and wild-derived mice with multiple loci for production of xenotropic murine leukemia virus.

Mendelian segregation analysis was used to define genetic loci for the induction of infectious xenotropic murine leukemia virus in several laboratory and wild-derived mice. MA/My mice contain two loci for xenotropic virus inducibility, one of which, Bxv -1, is the only induction locus carried by five other inbred strains. The second, novel MA/My locus, designated Mxv -1, is unlinked to Bxv -1 and shows a lower efficiency of virus induction. The NZB mouse carries two induction loci; both are distinct from Bxv -1 since neither is linked to the Pep-3 locus on chromosome 1. Finally, one partially inbred strain derived from the wild Japanese mouse, Mus musculus molossinus, carries multiple (at least three) unlinked loci for induction of xenotropic virus. Although it is probable that inbred strains inherited xenotropic virus inducibility from Japanese mice, our data suggest that none of the induction loci carried by this particular M. m. molossinus strain are allelic with Bxv -1.

Properties of mouse leukemia viruses XIX. Effective antibody therapy of AKR leukemia occurs independently of virus neutralization and produces long-term changes in the virus status of the thymus

Administration of high-titered goat anti-FLV gp71 IgG to AKR mice during a narrow neonatal therapy “window” suppresses the early development of MuLV infectious cell centers (ICC) in spleen, thymus, and bone marrow. By 4–5 weeks of age ICC appear in spleen and marrow cell populations, rapidly increasing to plateau levels within 2 weeks in the absence of viremia. The thymus of treated animals remains devoid of detectable ICC throughout the 4-month period of testing. This pattern of ICC suppression occurs independently of virus neutralization as shown by the inability of F(ab′) 2 preparations, which retained neutralizing activity, to prevent early establishment of ICC. Immune IgG significantly decreases, but does not eliminate gp71 expression in all tissues tested. In control animals, ICC reside within a minor subpopulation of cortical, thymic T cells, whereas peripheral (i.e., splenic) ICC are totally devoid of conventional T cell, B cell, and macrophage phenotypic markers. Although thymocytes appear to be a major target of this antibody therapy, T-cell reactivity is not compromised.

Induction of acute thrombocytopenia and infection of megakaryocytes by Rauscher murine leukemia virus reflect the genetic susceptibility to leukemogenesis.

Acute thrombocytopenia and megakaryocyte infection have been investigated during the preleukemic phase of the disease induced by the Rauscher murine leukemia virus (RMuLV) in mice. Injection of RMuLV, either intravenously or intraperitoneally, rapidly induced thrombocytopenia, possibly as a result of direct interaction between platelets and viral particles. The susceptibility to this acute thrombocytopenia was genetically controlled and was inherited as a dominant trait. Murine strains with H-2d or H-2k haplotype, which are susceptible to the induction of leukemia by RMuLV, developed thrombocytopenia, whereas leukemia-resistant H-2b and H-2q strains of mice failed to develop thrombocytopenia. Using B10 H-2-congenic and intra-H-2-recombinant mice, it was shown that the susceptibility to RMuLV-induced thrombocytopenia was controlled by gene(s) in or closely linked to the D region of the H-2 complex. Megakaryocytes may be one of the first sites for the replication of RMuLV. Indeed, among bone marrow cells, only megakaryocytes expressed viral antigens gp70 and p30 during the initial phase of RMuLV infection. In addition, megakaryocytes from infected mice were able to transfer preleukemic thrombocytopenia as well as leukemia in syngeneic mice. The infection of megakaryocytes by RMuLV appears to be genetically controlled in a manner similar to the induction of thrombocytopenia, since only the megakaryocytes from mice developing thrombocytopenia were infected by RMuLV. These results indicate that the gene(s) governing the induction of thrombocytopenia by RMuLV may be the same gene(s) (or closely linked to the gene) that controls the susceptibility to leukemogenesis, and would be consistent with the expression of the gene product, presumably a receptor-like molecule for RMuLV, on platelet and megakaryocyte membranes.

Mouse immunoglobulin antibodies require complement for neutralization of mouse retroviruses.

The addition of guinea pig complement was found to enhance the neutralizing capacity of mouse antibodies directed against the endogenous ecotropic murine leukemia viruses. The same immune sera, when tested without complement, had low or negligible neutralizing capacities, regardless of whether freshly harvested, unfrozen virus was used to preserve virus infectivity. Antibodies in high titers were found in sera from NFS congenic mice carrying the mouse leukemia virus inducing locus Akv-2. These mouse antibodies were type specific and failed to neutralize either Friend or Moloney leukemia virus. The mouse serum immunoglobulin fraction containing the complement-dependent antibodies was tentatively identified as immunoglobulin M.

Interferon-induced augmentation of natural killer cell activity by splenocytes from leukemia virus immunosuppressed mice.

Interactions of Friend leukemia virus (FLV) and immune responsiveness in mice has been studied extensively over the past decade (4). In most circumstances FLV has been shown to depress cellular and humoral immunity. However, the role of these depressed responses in the pathogenesis of this virus infection is not known. In this regard, our laboratory recently began investigation of natural killer (NK) cell activity in FLV infected BALB/c mice.KeywordsSpleen CellNatural Killer Cell ActivityNatural Killer ActivitySpleen Cell CultureSplenic Natural Killer CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Rauscher murine leukemia virus: molecular cloning of infectious integrated proviral DNA.

The integrated proviral genome of Rauscher murine leukemia virus was molecularly cloned in a bacteriophage Charon 4A vector after the proviral sequences were enriched by sequential RPC-5 column chromatography and sucrose gradient centrifugation. A recombinant DNA clone, lambda-RV-1, possessing a 12-kilobase-pair EcoRI insert, was shown to contain the entire 8.8-kilobase-pair leukemia virus genome flanked by rat cellular sequences at the 5' and 3' ends. This DNA fragment was biologically active, inducing the release of virion-associated reverse transcriptase activity with as little as 10 ng of DNA insert. The virus induced XC plaque formation at high titers on NIH/3T3 and BALB/3T3 cells and demonstrated identity with the parental virus in radioimmunoassays for the highly type-specific gag gene-coded p12 protein. The molecularly cloned Rauscher murine leukemia virus should be useful in studying the molecular mechanisms involved in the transformation of specific lymphoid target cells by chronic mouse leukemia viruses.

Murine T-lymphoma ‘immunoglobulin’ is identical to leukemia virus gp 70

We have used chicken anti-mouse immunoglobulin antiserum to precipitate molecules from mouse T-lymphoma cells that had been radioiodinated. We analysed the immunoprecipitates by two-dimensional gel electrophoresis and compared the results with immunoprecipitates generated by other antisera. We found that the molecule precipitated by chicken anti-mouse immunoglobulin from T-lymphoma cells was identical to the mouse leukemia virus envelope glycoprotein (gp 70) produced by the T-lymphoma. Mouse IgM myeloma proteins block precipitation of T-lymphoma molecules by chicken anti-mouse immunoglobulin. We conclude that mouse IgM and gp 70 share antigenic determinants. This may lead to erroneous conclusions about the presence of immunoglobulin on T-cells.

Properties of mouse leukemia viruses XVIII. Effective treatment of AKR leukemia with antibody to gp7l eliminates the neonatal burst of ecotropic AKR virus producing cells

To suppress spontaneous leukemia, treatment of AKR mice with antibody to the murine leukemia virus (MuLV) major glycoprotein (gp71) must commence during a narrow “window” period between birth and Day 3. To examine the effect of treatment on virus expression, infectious MuLV cell centers (ICCs), free MuLV, and viral antigen presence were examined in various organs of control and antibody-treated neonatal AKR mice. Ecotropic MuLV ICCs and viral antigens were found to increase 100-fold between Days 3 and 8 in thymuses, spleens, and livers in untreated mice. Quantitatively, spleens and livers had about 100-fold more viral ICCs than the thymus. After Day 8 viral ICCs persisted at plateau levels in all organs, with thymic ICCs 100-fold below spleens and livers. Maximal plateau levels of free ecotropic virus were reached only by Day 16. Xenotropic MuLV was occasionally isolated in ICC assays, but no recombinant MuLV was ever detected in any organ early in life. Viral p30 and gp7l antigen expression detected by immunofluorescent assays (IFA) closely corresponded to ICCs. In contrast, in AKR mice treated three or more times with gp7l antibody, MuLV ICCs were essentially undetectable during the first 3 weeks of life. In IFA, anti-gp7l-treated mice also had no virus antigen-positive cells in the organs tested. Spleen cells from control antibody-treated AKR mice were also treated in vitro with immune antibody and tested for virus- and antigen-positive cells. Anti-gp7l antibody did bind in vitro to virus-positive cells as measured by IFA but was neither cytotoxic nor reduced viral ICCs. However, the addition of complement to anti-gp7l antibody-coated cells resulted in a highly specific, effective killing of those cells scoring as viral ICCs. To determine the role of induction and/or clonal expansion of virus-positive cells relative to virus spread, perinatal F 1 (NIH × AKR) (by convention, maternal parent listed first in F 1 designations) and (BALB/c × AKR) mouse cells were assayed for ecotropic ICCs. Fv-1 n permissive (NIH × AKR) mice had only slightly fewer ICCs, and the timing and distribution of virus release was similar to AKR mice. Fv-1 nb restrictive (BALB/c × AKR) mice had different kinetics of ICC formation. At plateau, the ICCs were severalfold lower than that in Fv-1 n permissive mice, suggesting that an increase of virus-positive cells occurs during the neonatal period by means other than virus spread. However, virus spread may account for up to a 10-fold-increase in ICCs in AKR mice. The above data graphically demonstrated that the treatment “window” corresponded to a time just prior to the burst of ecotropic virus ICCs. The nature of ecotropic virus-positive cells and their elimination with treatment are discussed relative to later events in AKR leukemogenesis.

Suppression of spontaneous lymphoma by previously undiscovered dominant genes in crosses of high- and low-incidence mouse strains

Crosses of mice of the high-lymphoma mouse strains, AKR and C58, with mice of the low-lymphoma strains, C57L, DBA/1, and DBA/2, produce F 1 generations with low and late incidences of the spontaneous disease. Backcross populations, obtained from high-lymphoma parental strain × low-lymphoma F 1 coatings, showed lymphoma incidences of ⋍75%, indicating that the low lymphoma incidence in F 1 mice of these crosses was due to the simultaneous presence of at least two independently segregating dominant genes inherited from the low-lymphoma parental strain. In none of the three crosses was lymphoma resistance linked to the Fν-1 locus, and in only one (AKR × C57L) was H-2 type a significant determinant of the disease. This finding indicates that previously undiscovered genes possess the capacity to suppress spontaneous murine lymphoma. Studies of the expression of endogenous ecotropic and xenotropic murine leukemia viruses in mice of these crosses suggest that one of the new genes involved in lymphoma suppression may act by delaying the expression of xenotropic virus.

Complete amino acid sequence of the group-specific antigen gene-encoded phosphorylated proteins of mouse leukemia viruses.

The complete amino acid sequence of the group-specific antigen gene-encoded RNA binding phosphoprotein p12 has been determined for both Rauscher and Moloney leukemia viruses. Large fragments generated by acid, and cyanogen bromide and hydroxylamine cleavage, and Staphylococcus aureus V8 protease digestion were subjected to automated sequencing. Both Rauscher and Moloney p12 are composed of 84 amino acids arranged in alternating variable and conserved regions. The homology between the conserved internal and COOH-terminal regions is greater than 95%, but the NH2-terminal and internal variable regions show 59 and 51% homology, respectively. The role of such regions in the type-specific biological activities of these molecules is discussed.

Genetic control of sensitivity to moloney leukemia virus in mice. VI. Involvement of virus‐specific T helper cells collaborating with B cells

T cell responses to Moloney virus involve cytolytic and helper lymphocytes. In contrast to specific cytolytic T lymphocytes, few studies have been devoted to the characteristics of helper T cells for antibody production. The present experiments describe an assay for Moloney virus-specific help for B cells using dinitrophenylated virus. This method, using the Moloney virus as a carrier in a hapten-carrier system, allows to definition of the specific helper function of antibody responses. T helper cells were induced in murine sarcoma virus or inactivated Moloney murine leukemia virus-primed spleens or lymph nodes. T helper function was due to Thy-1.2, Lyt-1+2- cells and was macrophage-dependent. It was stimulated by whole virus of Moloney gp71 envelope protein but not Moloney p30 internal protein. Cross-reactive stimuli were obtained with other dinitrophenylated type C viruses. High and low responses were correlated respectively with resistance and susceptibility to Moloney leukemia virus. Cultures of helper T cells with preserved activity have been established and maintained for one month.

Genetic control of sensitivity to Moloney leukemia virus in mice V. Role of H-2-linked genes in the control of anti-FMR cytolytic T lymphocytes

Three H-2-linked genes, Rmv1, Rmv2, and Rmv3 control the resistance of mice against Moloney virus (MLV)-induced leukemias. It has been shown previously that they function as immune response (Ir) genes regulating the level of antivirus antibodies. In the present experiments, the cell-mediated anti-tumor response has been studied in a series of inbred strains selected for their resistance or sensitivity to the MLV-induced disease. We failed to detect any relationship between resistance and sensitivity and the ability to produce cytolytic T lymphocytes (CTL) directed against the virus-induced FMR cell surface antigen. Furthermore, the role of each Rmv gene has been studied separately using congenic pairs of mice differing at only one of these loci: we failed to evidence any influence of these genes in the cell-mediated antitumor reactions as measured by the ability to lyse syngeneic FMR(+) target cells. Nevertheless a gene mapping in the D region of the MHC but probably different from Rmv3 controls the response of a subset of anti-FMR CTL restricted by the H-2K k antigens, with higher response in H-2D d than in H-2D b animals. This observation confirms the existence of H-2D region associated Ir genes regulating the CTL-mediated antitumor immune responses by choosing the subset of responder CTL, and suggests that a fourth H-2-linked gene plays some role in the genetic control of the anti-FMR immune response.

Antibodies to mouse mammary tumor virus-related antigen in sera of patients with breast carcinoma.

Sera from patients with breast carcinoma, benign breast disease, malignancies other than breast carcinoma, and healthy female controls were analyzed by indirect immunofluorescence for the presence of antibodies directed toward antigens of mouse mammary tumor. Sera from 56 to 137 (40.9%) patients with breast carcinoma were positive. Positive reactivity was also found in sera from 5 to 27 (18.5%) patients with benign breast disease, in 7 of 60 (11.7%) patients with malignancies other than breast carcinoma, and in 2 of 56 (3.6%) female controls. In the group of patients with breast carcinoma a correlation was noted between age and the probability of detection of these antibodies. Histopathologic examination of breast cancers indicated that antibodies to antigens in mouse mammary tumors were more often found in patients with infiltrating ductal carcinoma of the mucinous type than with other types of breast tumors. No correlation was demonstrable between the incidence of detection of these antibodies and the stage of the disease. Immunochemical analyses indicated that the antibody activity was present in IgG and IgM classes of immunoglobulins. The human antibodies to antigens in mouse mammary tumors could be removed from patients' sera by absorption with disrupted mouse mammary tumor virus (MMTV) but not with gp52 or gp34 (52,000 and 34,000 dalton polypeptides) of MMTV, or with Rauscher mouse leukemia virus (MLV).

Properties of mouse leukemia viruses XVII. Factors required for successful treatment of spontaneous AKR leukemia by antibodies against gp71

AKR mice were treated with heterologous anti-gp71 antibodies under various conditions in order to establish the optimal criteria for effective suppression of leukemia development. The strongest effect was observed when mice were treated at birth; and when this regimen was used, prior treatment of the mothers did not provide additional protection. If treatment was delayed until Day 3 ( Schwarz et al., 1979 ), the beneficial effect of the serum diminished sharply, emphasizing the presence of a narrow window very early in the life of the AKR mouse when antibody must be present in order to have an effect on subsequent leukemia development. A number of parameters were examined in the experimental mice and as in our previous study ( Schwarz et al., 1979 ), suppression of leukemia, which occurred in 68% of the animals, correlated with elimination of viremia and appearance of natural antiviral antibodies. Interestingly, our results suggest that antibody therapy is primarily effective against the thymic form of the disease. The availability of nonviremic, antibody-positive animals afforded us the opporounity to examine if these characteristics could be transmitted to the offspring. From selected mating crosses, we successfully derived both F1 and F2 generations of AKR mice which possessed high titers of antiviral antibodies and were nonviremic at 21–28 weeks of age. It appeared that a maternal effect may be responsible for this phenomenon. The implications of these findings are discussed in relation to the development of AKR leukemogenesis.

Interferon-mediated inhibition of mouse mammary tumour virus (type B) and mouse leukaemia virus (type C) in the same culture.

The sensitivity of mouse mammary tumour virus (MMTV) and murine leukaemia virus (MuLV) to interferon was tested by investigating the effect of interferon in cultures of mouse mammary tumour cells simultaneously synthesizing the two viruses. The dose-response curves showed that the extracellular production of both viruses by these cells was equally inhibited by interferon treatment. In contrast, the intracellular steady-state concentration of virus-specific RNA of both MMTV and MuLV was not significantly affected in these cells. This was the case regardless of whether total cellular RNA or polysomal poly(A)-containing RNA was examined. These results are consistent with the suggestion that interferon-caused inhibition is related to a host-mediated effect on a post-transcriptional step in virus synthesis.

Expression of terminal deoxynucleotidyl transferase as related to the surface phenotype of M.MuLV-induced lymphomas

Terminal deoxynucleotidyl transferase has been assayed in lymphomas induced by Moloney leukemia virus in B10 and BALB mice and in derived cultured tumor cells. TdT is present only in Thy 1.2 + cells, and can be detected in tumoral spleen and lymph node only when the thymus itself is tumoral. The level of TdT is related to the cell surface phenotype. The expression of TdT can be correlated to the differentiative stages of the T-cell lineage.