Showing papers on "BALB/c published in 1970"

Common individual antigenic determinants in five of eight BALB-c IgA myeloma proteins that bind phosphoryl choline.

Abstract: Eight IgA myeloma proteins derived from independently induced plasma-cytomas in genetically similar inbred BALB/c mice are functionally related by their binding of phosphoryl choline-containing antigens (Pneumococcus C polysaccharide or Lactobacillus antigen) Each protein resembles a single species of immunoglobulin in antibody The proteins are characterized by highly sensitive myeloma-specific antisera prepared by immunizing mice of other inbred strains with the BALB/c myeloma proteins Individual or myeloma-specific determinants located on Fab fragments were found on three of the proteins that were unique for that protein and did not react with any other IgA protein among over 70 tested Remarkably, five of the proteins shared two common myeloma-specific determinants which were specific for this group of five proteins These results suggest that the five functionally and genetically related proteins sharing the same myeloma-specific determinants might also be structurally similar

Colony inhibition studies on blocking and non-blocking serum effects on cellular immunity to moloney sarcomas.

Abstract: Moloney-virus-induced sarcomas, originating in BALB/c and A/Sn mice, were studied with the colony inhibition (CI) assay. Mice inoculated with the virus as adults developed tumors which spontaneously regressed (regressors) while mice inoculated with the same virus dose at an age of 21 days or less died from progressively growing tumors (progressors). Serum from progressors blocked the colony inhibitory effect of lymph-node cells (LNC) from the regressors. Serum from mice inoculated with the virus as adults had a similar blocking effect as long as the mice carried progressively growing tumors, but it did not block the LNC effect when harvested at the onset of regression or after its completion. When regressor sera were mixed with progressor sera the blocking effect of the latter decreased.

Synergy among lymphoid cells mediating the graft-versus-host response. II. Synergy in graft-versus-host reactions produced by Balb-c lymphoid cells of differing anatomic origin.

Abstract: The capacity of cells from different lymphoid tissues obtained from Balb/c mice to produce graft-vs.-host (GVH) reactions was quantitatively determined in C57BL/6N by Balb/c F(1) hybrid recipients. Synergistic responses were observed when small numbers of cells from lymphoid tissues that were rich in GVH activity such as spleen and femoral lymph node were combined with weakly reactive thymus cells. Thymus and spleen cells obtained from 1-wk old mice were separately inactive but produced moderate GVH reactions when combined in equal proportions. GVH activity of spleen cells from mice thymectomized at 3 days of age was partially restored by the addition of small numbers of spleen or thymus cells from adult mice. Changes in ratio between the two cell populations markedly affected the degree of synergy. Synergy was not observed when Balb/c cells were combined with Balb/c x C57BL/6N F(1) hybrid cells and inoculated into C57BL/6N recipients, but was demonstrated when Balb/c and C57BL/6N cells were combined and inoculated into F(1) recipients, indicating that a genetic disposition to mount GVH reactions in both populations is required to produce synergy. The data indicate that at least two cell types are necessary for GVH reactions, and that synergy between cell populations results from favorable adjustments in the ratio between these two cell types.

Immune responses of inbred mice to repeated low doses of antigen: relationship to histocompatibility (H-2) type.

Abstract: Immunization of inbred strains of mice with repeated minute doses (0.1 to 1.0 microgram) of hapten-protein conjugates demonstrated wide differences in the magnitude of their antibody responses, which were related to the histocompatibility (H-2) type of the strains. Immunization with a single high dose (100 micrograms) of antigen failed to demonstrate these differences.

A sex-limited serum protein variant in the mouse: inheritance and association with the H-2 region.

Abstract: An alloantiserum produced in the mouse has been used to detect an antigen which is present only in male serum from certain inbred strains of mice, e.g., DBA/2J, A/J, and BALB/c. Genetic tests reveal that the presence of this antigen is controlled by a dominant autosomal gene which is expressed only in males of the proper genotype. Test crosses and analysis of congenic resistant strains indicate close linkage between the sex-limited protein (Slp) and the histocompatibility-2 (H-2) region of linkage group IX. Analysis of seven intra-H-2 recombinant strains is consistent with the placement of the genetic determinant for Slp within the H-2 region in the same position as the Ss (serum substance) determinant. Immunological evidence suggests that the Slp antigenic sites reflect structural variation in the Ss component of mouse serum.

Chronic allogeneic disease. II. Development of lymphomas.

Abstract: The incidence of lymphomas in 371 CAF1 mice injected with BALB/c spleen cells was compared with that in 324 control CAF1 mice. A high incidence of lymphomas was found in the treated mice, but not in the control animals. The development of the neoplasms was a function of the number of parental cells administered. Analyses of the injected mice for the presence of donor cells indicated that the majority of the injected parental cells lost antihost activity, probably within 24 hr of their administration. The tumors were of host origin, as judged by transplantation tests and antigenic analysis of tumor cells.

Leukemia Virus Activation in Chronic Allogeneic Disease

Abstract: Young adult (BALB/c × A/J)F1 hybrid mice have no detectable leukemia viruses. When inoculated with parental BALB/c spleen lymphoid cells, also free of detectable virus, leukemia viruses rapidly become activated in the injected host. Because of similarities between such graft-induced allogeneic disease and spontaneous autoimmunity, it is proposed that autoimmune reactions may activate latent viruses.

Influence of prednisolone on Moloney leukemogenic virus in BALB-c mice

Abstract: Summary Long-term administration of prednisolone to BALB/c mice alters the reactivity of their lymphoid tissue to the oncogenic effects of Moloney leukemia virus. Solid lymphosarcoma or granulocytic leukemia is produced in a significant number of the treated mice. The alteration in disease response may be attributed to a prednisolone-induced simulated thymectomy.

Studies on the immune responses of BALB/c mice during tumor induction by mineral oil

Abstract: The immune responses to a number of different antigens were tested under the influence of mineral oil treatment in two strains of mice: BALB/c, which is susceptible to oncogenesis by intraperitoneal administration of oil, and C57Bl, which is resistant. A limited, but general, immunological depression was elicited by the oil treatment in the BALB/c, but not in the C57Bl, animals. Immunogenicity studies on tumors induced by mineral oil in BALB/c mice suggest that this category of neoplasms also possesses tumor-associated antigenicity. The findings are discussed in relation to the role which may be played by dysfunction of the immune response in carcinogenic action. ETUDE DES REPONSES IMMUNOLOGIQUES DES SOURIS BALB/c AU COURS DE L'INDUCTION DE TUMEURS AU MOYEN D'HUILE MINERALE Les reponses immunologiques a differents antigenes ont ete testees apres administration d'huile minerale a deux souches de souris: BALB/c, pour qui l'administration intraperitoneale d'huile minerale est carcinogene, et C57B1 qui est une souche resistante. Une depression immunologique generale, bien que limitee, a ete obtenue par ce traitement chez les souris BALB/c, mais pas chez les C57B1. L'etude immunologique des tumeurs induites par l'huile minerale chez les souris BALB/c donne a penser que cette categorie de neoplasmes possede aussi une antigenicite liee a la tumeur. Les auteurs exposent leurs constatations en tenant compte du rǒle eventuel d'un mauvais fonctionnement de la reponse immunologique a l'action carcinogene.

The Effect of Polyinosinic-Polycytidylic Acid Upon Graft-vs-Host Activity in BALB/c Mice

Abstract: Natural and synthetic polymers of nucleic acids have been shown to enhance humoral antibody responses to sheep red blood cells and bovine γ globulin (1–4). The double stranded RNA, polyinosinic-polycytidylic acid (poly I:poly C), is a potent inducer of interferon production (5) and recently has been demonstrated to inhibit the growth of some types of tumors in mice (6). One explanation for the anti-tumor activity of poly I:poly C may be that it acts as an adjuvant in cellular immune reactions, causing enhanced immunologic rejection. In order to test this hypothesis, spleen cells obtained from animals that were treated with poly I:poly C were injected into neonatal recipients. Graft- vs -host (GVH) reactions that resulted were compared to those obtained with spleen cells from untreated donor animals using a quantitative spleen-weight assay. Materials and Methods. A modification (7) of the spleen assay described by Simonsen (8) was performed. The assay is based upon the observation that splenomegaly in recipient neonatal F 1 mice is an early and constant finding following injections of lymphoid cells obtained from mice of one parental strain.

Effect of partial hepatectomy on tumor incidence in BALB-c mice treated with urethan.

Abstract: on Urethan Carcinogenesis in C3H/f Mice. Cancer Res., 24: 1869—1879, 1964. 15. Mirvish,G., Cividalli, G., and Berenblum, I. Slow Elimination of Urethan in Relation to Its High Carcinogenicity in Newborn Mice. Proc. Soc. Exptl. Biol. Med., 116: 265—268, 1964. 16. Pietra, G., Rappaport, H., and Shubik, P. The Effects of Carcino genic Chemicals in Newborn Mice. Cancer, 14: 308—317, 1961. 17. Pound, A. W. Carcinogenesisand Cell Proliferation. New Zealand Med. J., 67: 88—99,1968. 18. Pound, A. W., and Withers, H. 0. The Influence of Some hritant Chemicals and Scarification on Tumor Initiation by Urethan in Mice. Brit. J. Cancer, 17: 460—470,1963. 19. Rosen, V. J., and Cole, L. J. Acceleration Induction of Kidney Neoplasms in Mice after X-irradiation (690 RAD) and Unilateral Nephrectomy. J. Nat!. Cancer Inst., 28: 1031—1041, 1962. 20. Snedecor, G. W., and Cochran, W. G. Statistical Methods, Ed. 6. Ames, Iowa: Iowa State University Press, 1968. 21. Tannenbaum, A., and Silverstone, H. Urethan (Ethyl Carbamate) as a Multipotential Carcinogen. Cancer Res., 18: 1225—123 1, 1958. 22. Toth, B., Della Porta, G., and Shubik, P. Occurrence of Malig nant Lymphomas in Urethan-treated Swiss Mice. Brit. J. Cancer, 15:322—326, 1961. 23. Yokoyama, H. 0., Wilson, M. E., Tsubol, K. K., and Stowell, R. E. Regeneration of MouseLiverafterPartial Hepatectomy. Cancer Res., 13: 80—85,1953. Effect of Partial Hepatectomy on Tumor Incidence in BALB/c Mice Treated with Urethan'

Genetic control of the specificity of anti-dnp antibodies. II. Differences in the specificity of anti-dnp antibody produced by several inbred strains of mice.

Abstract: Differences in the fine specificity of anti-2,4-dinitrophenyl (DNP) antibodies produced by different inbred mouse strains were demonstrated. These differences are expressed in terms of the relative capacity of a given nitrophenyl ligand to inhibit the binding of 3H-DNP-∈-aminocaproic acid (3H-DNP-EACA) by anti-DNP antibodies. The most prominent differences concerned the relative affinity of AKR and of BALB/c anti-DNP antibodies for 2,4-dinitrophenol and 2,4-dinitroaniline and the relative affinity of AL/N and C57BL/6 anti-DNP antibodies for picryl-e-aminocaproic acid. These strain-specific fine specificity patterns could not be explained by systematic differences in average association constant for 3H-DNP-EACA. The specificity patterns of anti-DNP keyhole limpet hemocycanin and anti-DNP bovine γ globulin antibodies produced by a given strain were generally similar. The differences in fine specificity pattern between AKR and BALB/c anti-DNP antibodies were noted in antisera collected at various times in the course of the immune response. Strain-determined variation in the fine specificity of anti-DNP antibodies may present a model system for studying the genetic control of antibody specificity.

Production of Leukemia and Stomach Neoplasms in Swiss, RF, BALB/c, and C3H Female Mice by Feeding N-[4-(5-Nitro-2-furyl)-2-thiazolyl]acetamide

Abstract: Summary N -[4-(5-Nitro-2-furyl)-2-thiazolyl]acetamide was fed to female 5-week-old Swiss mice at a dose of 0.1% by weight of diet for 13 weeks, with a cumulative dose of 490 mg/mouse/13 weeks. The mice were observed for an additional 14-week period while being fed control diet. Because of the sudden appearance of leukemia during the 13th week and cannibalization of moribund mice by other mice, only 16 mice survived at least 17 weeks to be grossly and microscopically evaluated. Of these, 15 had generalized lymphocytic leukemia and 3 had squamous cell tumors of the stomach. In the control group of 56 mice, no cancers were detected during the 27-week period of observation. For determination of the effect of dosage, groups of 30 female 5-week-old Swiss mice were fed NFTA at dietary levels of 0.1, 0.05, 0.025, and 0.01% for 14 weeks. The respective leukemia incidences were 8/9, 9/13, 8/16, and 7/14. The latent period was 12 weeks for the 0.1 and 0.05% groups and 18 weeks for the 0.025 and 0.01% groups. Stomach tumors were present in 12/52 mice. In the control group of 35 mice, 1 mouse developed a pulmonary adenoma. RF, BALB/c, and C3H female mice, regarded as having a low incidence of spontaneous leukemia, were as susceptible to the leukemogenic effect of NFTA as were Swiss mice. The following incidences of leukemia were observed after 14 weeks of feeding a diet composed of 0.1% NFTA: RF, 12/16 (controls, 3/16); BALB/c, 21/29; C3H, 12/24; and Swiss, 22/22. A low incidence of stomach tumors was found in all NFTA-treated groups.

Allograft immunity in vitro. 3. Induction of deoxyribonucleic acid synthesis in mixed cultures of mouse peripheral lymphocytes from inbred strains differing at non-H-2 loci.

Abstract: By using cultures of allogeneic mouse peripheral lymphocytes, it was possible to show that antigens determined by the major histocompatibility locus are not solely responsible for the mixed lymphocyte interaction. In some cases, using pairs of inbred strains which have the same H-2 genes but differ at multiple non-H-2 loci, a proliferative response was obtained.

The Predictive Value of Skin Allograft Survival Times during the Development of Urethan-induced Lung Adenomas in BALB/c Mice

Abstract: Summary The possibility that depression of cell-mediated immunity facilitates the carcinogenic effect of urethan on the mouse lung was studied in the BALB/c strain which is highly susceptible to lung tumor development. Lung adenomas were induced by giving 4-day-old mice an i.p. injection of 1.0 mg urethan. Two months after injection, urethan-treated and 0.85% NaCl solution-treated control mice were test grafted with DBA/2 skin ( H-2 d → H-2 d ). In the 1st experiment, urethan caused a modest impairment of graft rejection as indicated by a skewing and flattening of the normal distributions of survival scores in treated mice: 64% of 36 urethan-treated mice had rejection times slower than the control median. Two months after grafting, lung adenomas were found preferentially in these mice rather than in mice with shorter rejection times. In the 2nd experiment, thymectomy and sham thymectomy were performed 2 to 3 days before urethan treatment. Thymectomized mice of both sexes developed significantly more lung adenomas than did sham-thymectomized controls. Thymectomized males, but not females, had significantly larger adenomas than did controls. Among males, large adenomas occurred in slow allograft rejectors more frequently than expected by chance. Deaths from large, obstructive lung adenomas occurred exclusively among the slowest rejectors whether or not they had intact thymuses. Based on the combined data of the 2 experiments, allograft survival scores were significantly correlated with lung adenoma incidence. We concluded that skin allograft survival scores after urethan treatment provide a useful index of the risk of lung tumor development in BALB/c mice. This relationship can be explained by assuming that cell-mediated immunity normally modifies the expression of the carcinogenic effect of urethan on the mouse lung. Our findings are interpreted as further evidence for the operation of immunological surveillance during chemical carcinogenesis.

Search for cross-reacting antigenicity between mammary tumor virus-induced mammary tumors and embryonic antigens: effect of immunization on development of spontaneous mammary tumors.

Abstract: DepartmentofBacteriologyandImmunology,andtheCancerResearchGeneticsLaboratory,UniversityofCalifornia,Berkeley,California94720Evidencehasbeenaccumulatingintheliteraturethatatleastsomeoftheantigenscharacteristicallyfoundintumorsmayrepresentthereappearanceofembryonictissueantigensthatarenotnormallyfoundintheadult(1,4,7—9,11).Theexperimentsdescribedhereinwereundertakentodeterminewhethertheremightexistarelationshipbetweenembryonicantigensandeithertheviral-associated(5)orthenonviral(12)antigensfoundinmammarytumorswhichdevelopintheMTV2-infectedmouse.Theseviral-associatedandnonviralantigenshavebeendetectedbytransplantationprocedures,andthusitseemedprofitabletodetermineifpretreatment withembryonictissuescouldinfluencethenormaldevelopmentofspontaneoustumors,byalteringeithertumorincidenceortheageatwhichthetumorsdevelop.Emphasiswasplacedontheuseofembryonicandneonataltissuefromtheventralsurfaceofthemouse,whichincludestheareasinwhichthemammaryanlageareundergoinggrowthanddevelopmentduringlatefetallife.Pretreatmenteitherbyinjection oftissueextracts orbyimplantationoftissuefragmentswascarriedout.Byvaryingtheparityoftheanimals,andthereforetheamountofhormonal stimulation, whichinfluencesboth tumorincidenceandageoftumordevelopment(2),itwaspossibletodeterminewhethertumordevelopmentwaseitherdecreasedorenhancedbytheimmunizationprocedures.Inadditiontothegroupsreceivingvariousembryonictissues,somegroupswerepretreated witheithermammaryglandormammarytumortissue.Othergroupsreceivedonlyinjections of0.85%NaC1solution. Allrecipients wereBALB/cfC3Hfemales,neonatallyinfectedwiththemammarytumorvirus,andthereforesusceptibletothe“spontaneousâ€sdevelopmentofmammarytumorsinadultlife.Thetissuesusedforpretreatmentwereeitherallogeneic,obtainedfromA/Crglstrain,orsyngeneic,obtainedfromtheBALB/cCrglandtheBALB/cft3HCrgl strains.Someofthe

Spleen foci and polycythemia in C57B1 mice infected with host-adapted Friend leukemia virus.

Abstract: The host range of Friend leukemia virus was altered significantly by passage in newborn C57Bl mice. Two virus isolates (BSB and BB6), derived from the original Friend virus stock, induced the familiar “Friend disease” and polycythemia in suckling or adult C57Bl mice. However, both isolates differed from the parent virus in Swiss mice by their longer latent period and lower mortality in adult C57Bl mice. Replication of spleen focus-forming virus (SFFV) from either isolate was limited in suckling mice and barely detectable in adult C57Bl mice. Host susceptibility to SFFV in the BSB isolate varied according to age in young adult C57Bl mice, and was also affected by a gene closely linked with or at the Histocompatibility-2 locus. Spleen focus formation by either BSB or BB6 in adult BALB/c mice gave one-hit dose-response relationships, in contrast to the multiple-hit relationship obtained with the parent virus. Thus, infection of C57Bl mice with either of two host-adapted viruses resulted in the development of polycythemia and splenomegaly without extensive SFFV replication, in contrast to earlier observations with the original Friend virus preparation in Swiss mice. Even with the present virus-host system, however, there was an association between virus replication and the virulence of the induced disease. In addition, there was an association between adaptation of SFFV to the C57Bl strain and an increased concentration of either helper virus or competent virions. Reasons for the low virus titers in several mouse strains and for the limited virus replication in the two strains tested were not apparent.

Histoproliferative effect of Rauscher leukemia virus on lymphatic tissue. II. Antigen-stimulated germfree and conventional BALB-c mice.

Abstract: SummaryNormal and antigenically stimulated germfree BALB/c young adult mice were used as a test system for studying the role of the nonthymus-dependent and thymus-dependent lymphoid tissue in Rauscher leukemia virus infection. It was considered that the splenomegaly of Rauscher disease within a germfree population would be enhanced by the establishment of active germinal centers in the nonthymus-dependent region of the lymphatic nodules of mice previously immunized with sterile sheep erythrocytes (SRBC). Similar comparisons were made in conventional BALB/c mice in which SRBC and lactic dehydrogenase virus were used as the test antigens. Results of these studies demonstrate the necessary, if not essential, role of the antigen-retaining reticular cells and immunoblasts of lymphatic tissue germinal centers in the early lymphoblastosis and subsequent splenomegaly of Rauscher disease. In addition, morphologic results strongly suggest the differential effect of the Rauscher preparation on the thymus- and nonthy...

Ovarian Influence on Pulmonary Carcinogenesis by Hydrazine Sulfate in BALB/c/Cb/Se Mice

Abstract: Daily administration of hydrazine sulfate, 1.13 mg/mouse for 150 doses, to BALB/c/Cb/Se female mice in various hormonal states varied the incidence and the average number of pulmonary tumors per tumor-bearing mouse as follows: in intact virgins, 90.0% and 3; in breeders, 100% and 14; in gonadectomized mice, 60.0% and 5. Histologically, in intact virgins, 3.3% were carcinomas and 96.6% were adenomas; in breeders, 47.2% were carcinomas and 52.7% were adenomas; in gonadectomized mice, 4% were carcinomas and 96% were adenomas. Many pulmonary carcinomas induced in breeders infiltrated the thoracic wall and the mediastinal organs and metastasized to the adrenal glands and myocardium. The greater biologic and morphologic malignancy of the induced tumors observed in breeders, as compared to those in intact virgin and gonadectomized mice, was associated with an increased ovarian hormone production.

Circulating Interferon Production in the Mouse : Origin and nature of cells involved and influence of animal genotype.

Abstract: A radiobiological study of circulating interferon production in the mouse was undertaken in the hope of elucidating the site(s) of circulating interferon production. After total body X-irradiation of the animals, different radiosensitivities of circulating interferon production were observed with different viral inducers. Myxovirus-induced circulating interferon production was especially radiosensitive. Moreover, a study of interferon production in syngeneic and xenogeneic radiochimeras demonstrated that cells producing NDV (Newcastle disease virus)-induced circulating interferon were derived from hematopoietic stem cells. In addition, treatment of mice with antilymphocyte serum significantly reduced NDV- and Sendai virus-induced circulating interferon, as opposed to other inducers. Taken together, these results strongly suggest that the lymphocyte is the major source of myxovirus-induced circulating interferon. A survey of interferon production in 12 inbred mouse strains, using NDV as inducer, revealed the existence of low and high producers. A Mendelian analysis carried out with low producing Balb/c and high producing C57BL indicated that the difference between low and high interferon producers was caused by a single, autosomal, codominant factor.

Tumor-specific humoral antibodies against plasma cell tumors in immunized BALB/c mice.

Abstract: In BALB/c mice immunized with plasma cell tumors incubated in sodium iodoacetate, antibodies against plasma cell tumors were detected by the indirect fluorescent antibody test. Fluorescence indices were determined in individual sera of animals bled at different intervals. After completion of immunizing injections, the time of appearance, level, and duration of antibodies depended on the number of injections. Cross-reactions and cross-absorption of antisera with several transplant lines of plasma cell tumor detected antibodies against individual tumor antigens and antibodies against antigen common to several plasma cell tumors. A relationship between antibody level, as detected by the fluorescence index, and resistance of animals to tumor graft could not be established.

Virus-like Particles in Chemically Induced Sarcomas in High- and Low-Leukemia Strains of Mice

Abstract: Well-differentiated fibrosarcomas and anaplastic sarcomas developed in the sc tissues of four low-leukemia strains of mice (BALB/cf/Ki, Af/Ki, C3H/Ki and C3Hf/Ki) as well as two high-leukemia strains (AKR/Ki and C58/Ki) following a single injection of benzpyrene (0004 mg/g body weight) as young adults The incidence of sarcomas was significantly less in both high-leukemia strains than that in all four low-leukemia strains Abundant type C murine leukemia virus particles were found in primary and transplanted sarcomas of AKR and C58 origin as well as in normal tissue of either tumor-bearing or non-tumor-bearing mice Type C virus particles were seen less frequently in primary and transplanted sarcomas arising in BALB/cf, C3Hf, and C3H mice No virus-like particles were seen in either primary or transplanted sarcomas or normal tissues obtained from Af mice Intracisternal type A virus particles were also seen in both primary and transplanted tumor tissue as well as normal tissue of AKR and C58 mice but not in the tumor or normal tissue of the other four strains Type B mammary tumor virus particles were not seen in any sarcomas developing in any strain of mouse Cell-free extracts of Af transplanted sarcomas in which no virus-like particles could be seen by electron microscopy proved to have biological activity when injected into newborn mice of the BALB/cf/Ki, C3Hf/Ki, C57BL/Ki, and Af/Ki strains This activity was characterized by an increased incidence of the tumors, which occur in low to moderate incidence in these strains No sarcomas were seen in any of the injection-treated mice of any strain Cell-free extracts of transplanted AKR sarcomas with abundant type C virus particles had no oncogenic effects when injected into newborn BALB/cf mice Whereas an extract of the 1st transplant generation of C58 sarcomas with abundant virus particles was negative when injected into newborn BALB/cf mice, an extract from the 8th transplant generation of sarcomas was associated with an increase in lung tumors in the same strain of mice These results indicate the complexity of the interactions between host genetic factors and the different murine oncogenic viruses found in chemically induced sarcomas A relationship between the virus-like particles found in these sarcomas and their etiology was not established