Retroviral induction of acute lymphoproliferative disease and profound immunosuppression in adult C57BL/6 mice.

We have shown that a mixture of murine leukemia viruses (MuLV) causes the acute onset of lymphoproliferation and immunosuppression when injected into adult C57BL/6 mice. The ecotropic/MCF (mink cell focus-inducing) mixture of MuLV stimulates polyclonal B lymphocyte proliferation and differentiation to antibody-secreting cells. Serum Ig levels are elevated for all isotypes except IgA. The viral infection leads to a rapid decline in T lymphocyte responses to mitogens and alloantigens, as well as a decrease in helper cell activity. Specific antibody responses to both T-dependent and T-independent antigens are impaired, and the response of B lymphocytes to mitogens is abolished. The profound immunosuppression seems to be due to the MuLV-induced polyclonal activation of lymphocytes. No active suppression of normal lymphocyte responses by cells from virus-infected mice was observed. The disease induced by the LP-BM5 MuLV isolate thus seems a promising model for the study of lymphocyte activation and the mechanisms of retrovirus-induced immunosuppression.

A mouse gene on chromosome 5 that restricts infectivity of mink cell focus-forming recombinant murine leukemia viruses.

DBA/1, DBA/2, CBA/N, and CBA/Ca mice carry a gene which specifically restricts infectivity of mink cell focus-forming (MCF) murine leukemia viruses. The gene, designated Rmcfr, is dominant or semidominant and maps to chromosome 5; it is closely linked to the morphologic marker gene Hm. The Rmcf gene may be of much use as a means of determining the role of MCF viruses in various forms of leukemogenesis.

Functional T lymphocytes are required for a murine retrovirus-induced immunodeficiency disease (MAIDS).

Athymic nu/nu mice were found to be resistant to the immunodeficiency disease and lethality induced in normal mice by the injection of the LP-BM5 mixture of murine retroviruses (LP-BM5 MuLV). Susceptibility to disease induction was reconstituted by injection of nu/nu mice with purified, mature T lymphocytes. The extent of viral replication of both the ecotropic and mink cell focus forming (MCF) components of LP-BM5 MuLV was equivalent in both nu/nu and normal animals. Retrovirally-induced immunodeficiency disease in mice (MAIDS) is thus dependent upon the presence of functional T lymphocytes, and high virus titers in athymic mice have little or no effect on the immune system.

CD4+ T cells are required for development of a murine retrovirus-induced immunodeficiency syndrome (MAIDS).

Mice depleted in vivo of CD4+ Th cells by treatment with mAb GK1.5 were found to be resistant to the lymphoproliferative/immunodeficiency disease (MAIDS) induced in intact mice by infection with the mixture of LP-BM5 murine leukemia viruses. Depleted mice did not develop lymphadenopathy or splenomegaly, had normal serum IgM levels, normal CTL responses to alloantigens, and were able to generate PFC responses to Th-independent antigens even though frequencies of virus-producing spleen cells were comparable in depleted and intact mice. Depletion of CD4+ Th cells after infection resulted in a reversal of many abnormalities exhibited by infected controls; spleen weights, serum IgM levels, and allogeneic CTL responses of treated mice were comparable to those of uninfected controls. These results demonstrate that dysfunction of CD4+ Th cells is central to the induction and progression of both T and B cell abnormalities in MAIDS.

Expression and modulation of a retrovirus-associated antigen by murine melanoma cells.

The antigen recognized by the monoclonal antibody MM2-9B6 is specific for melanomas originating in C57BL/6 mice. It is expressed by three melanomas of independent origin and not by normal or fetal tissues, by a wide variety of other nonmelanoma tumors in C57BL/6 mice, or even by melanomas syngeneic to other strains of mice. We have demonstrated that the expression of the relevant antigen is dependent on the replication and budding of a B-tropic ecotropic murine retrovirus. The relationship between the expression of this virus and carcinogenic progression may yield important insights into the cascade of events leading to neoplastic transformation.

ZDV delays but does not prevent the transmission of MAIDS by LP-BM5 MuLV-infected macrophage-monocytes.

LP-BM5 MuLV infection of monocyte-macrophages (MM cells) and the ability of MM cells infected with this murine oncornavirus complex to transmit murine acquired immune deficiency syndrome (MAIDS) were assessed. Adherent cells expressing Mac-1 antigen (Mac-1+) were isolated from the peritoneum of infected C57BL/6 mice at weekly intervals postinoculation. A small percentage of MM cells was infected by 7 days after inoculation with LP-BM5 MuLV and virus production could be detected in MM cells throughout the course of disease. MAIDS could be induced in naive C57BL/6 mice by i.p. injection of 0.5-3 x 10(5) MM cells derived from infected mice as early as 8 weeks postinfection. When 3 x 10(5) cells (300 infectious centers) were injected, the progression of disease was similar to that seen after inoculation with a known virus pool (log10 5.78 XC pfu/ml). Treatment with zidovudine (ZDV) at 1 mg/ml in drinking water delayed disease progression if started 24 h prior to inoculation of MM cells and given continuously.

Liver cell dysplasia: a DNA aneuploid lesion with distinct morphologic features.

Liver cell dysplasia is characterized by hepatocellular foci with nuclear atypia. It is often seen in cirrhosis and may be a precursor of hepatocellular carcinoma (HCC). To determine whether liver cell dysplasia is DNA aneuploid, 72 sections of 33 cirrhotic livers from the autopsy files of The Johns Hopkins Hospital were studied, and 14 foci of dysplasia from 13 cirrhotic livers were selected. Patients ranged in age from 32 to 70 years. Histologically, there were 10 foci of low-grade dysplasia and four foci of high-grade dysplasia. Nine HCCs served as positive controls; seven autopsy livers with no morphologic or clinical evidence of primary liver disease served as negative controls. One focus of HCC and one focus of dysplasia were unsatisfactory for analysis. Flow cytometric examination demonstrated subpopulations with DNA abnormality in four of nine (44%) foci of low-grade dysplasia, of which three were aneuploid. Three of four (75%) foci of high-grade dysplasia were aneuploid. Six of eight (75%) HCCs showed DNA abnormality, of which five were aneuploid. DNA aneuploidy was not present in the seven control livers; however, one showed DNA abnormality. We conclude that liver cell dysplasia is a morphologic entity that contains DNA aneuploid cells, a feature that supports the role of liver cell dysplasia in the evolution of HCC.

DNA analysis of cardiac myxomas: flow cytometry and image analysis.

Cardiac myxoma is the most common primary tumor of heart, but there is a longstanding controversy over whether it is a true neoplasm or a reactive lesion. We analyzed 24 cardiac myxomas from 22 patients: 22 by DNA flow cytometry and five by image analysis. Two myxomas were aneuploid; one of those analyzed by flow cytometry, and the other by image analysis. Proliferative fractions (S + G2/M) were high in three tumors from patients with multiple myxomas (mean, 15.9%; SD, 4.0%) as compared with 12 solitary uncomplicated myxomas (mean, 7.7%; SD, 6.0%). S-phase and proliferative fractions were low in embolic, recurrent, and solitary myxomas. The presence of aneuploidy in some myxomas supports a neoplastic origin for this tumor.

Effect of 3'azidothymidine administered in drinking water or by continuous infusion on the development of MAIDS.

LP-BM5 MuLV infection of C57BL/6 mice induces a well characterized, lymphoproliferative, immunodeficiency disease (MAIDS), which is useful for evaluation of potential antiviral agents, because of the reproducibility of virological and clinical endpoints. This MAIDS retrovirus model was used to evaluate 3'azido-2,3'dideoxythymidine (AZT), using different doses, methods of administration and timing for initiation and continuation of therapy. AZT therapy 1 mg/ml in the drinking water given 30 days prior to virus challenge, and continued for 16 weeks, prevented LP-BM5 MuLV dissemination and disease in 13 of 15 treated mice. Efficacy was dose dependent for AZT concentrations of 1, 0.5, and 0.1 mg/ml in drinking water. One mg/ml AZT was most effective in preventing infection if therapy was begun within days prior to virus challenge or within the first four hours after virus inoculation. If treatment was initiated later, disease was delayed. Continuous infusion of AZT, 25 micrograms/h, was effective since virus was not detected in spleens of any mice during the 21 days of AZT treatment. However, after treatment was stopped treated mice became virus positive and disease progressed. Likewise, AZT administration at 1 mg/ml in the drinking water for only 21 days post virus inoculation (p.i.), was not sufficient to prevent virus dissemination or disease.

Epithelioid component of uterine leiomyosarcoma simulating metastatic carcinoma.

A variant of uterine leiomyosarcoma containing two morphologic bell populations is described. A smooth-muscle component with a mitotic rate of 13 per 10 high-power fields, and a second population of cells mimicking metastatic small-cell carcinoma were both present. The second population was composed of small angulated epithelioid cells with hyperchromatic nuclei and barely discernible cytoplasm growing in tight rows, often in single file between fascicles of smooth muscle. DNA flow cytometry showed a large tetraploid aneuploid tumor cell population, and further suggested that the epithelioid cells probably represent tetraploid tumor cells in S-phase. Thus, this morphologic variant of leiomyosarcoma, unlike previously described variants of smooth-muscle tumors, is explained by the variable appearance of the neoplastic cells in different phases of the cell cycle.

Anti-nuclear antibodies in murine alloantisera are not necessarily related to antibodies to murine leukemia viruses.

Murine alloantisera often contain antinuclear antibodies. Frequently, these sera also have antibodies to murine leukemia viruses. In order to evaluate the relationship of these activities several alloantisera were tested for the presence of antinuclear and antiviral antibodies. The results of this study show that there is neither quantitative nor qualitative correlation between antinuclear and antiviral antibodies.

Cell surface antigen phenotypes of MCF-induced thymic lymphomas in AKR mice.

The hypothesis that the surface antigen phenotypes of MCF-MuLV-induced thymic lymphomas in AKR mice are predictable and characteristic of the inducing virus has been tested. Thymic lymphomas induced by two different MCF-MuLV were assayed by flow microfluorometry for their expression of the surface antigens XenCSA, Thy-1.1, Ly-2, Ly-1, 2C2, H-2K, and Ia. In all cases there was an increase in XenCSA levels. The lymphomas could be divided into three categories on the basis of qualitative difference in Ly-2 expression: Ly-2+ tumors, Ly-2- tumors, and tumors with both Ly-2+ and Ly-2- populations. One lymphoma expressed 2C2, an antigen not normally found on thymocytes. Quantitative differences in expression could be found for all antigens. This variation in surface antigen phenotype was independent of the cloned virus MCF used to induce the lymphoma.

Heterotypic immunity to influenza in ferrets.

Heterotypic immunity to influenza virus in ferrets operated against heterotypic influenza viruses but not heterologous viruses. Contrary to prior reports, the protection conferred lasted for at least 18 months. This type of immunity limited virus shedding but did not prevent infection. These results suggest that this phenomenon could play a role in determining the severity of infections caused by type A influenza viruses in humans.

Characterization of ecotropic murine leukemia viruses in SJL/J mice.

Backcross mice assorting for the two ecotropic murine leukemia virus loci of SJL/J mice (Emv-9 and Emv-10) were tested for production of infectious leukemia viruses. It was found that tail tissue from mice carrying Emv-9 could not be induced to produce ecotropic MuLV whereas tail tissue from mice carrying Emv-10 were inducible. No mice showed detectable levels of spontaneous virus production. Preliminary restriction enzyme analyses indicated Emv-9 contains a deletion within the polymerase region.

H-2-linked regulation of xenotropic murine leukemia virus expression.

A high proportion of lymphocytes from F/St mice produce infectious xenotropic murine leukemia virus (X-MuLV) and express high levels of cell surface antigens, termed XenCSA, related to the major glycoprotein of X-MuLV. In crosses of F/St with AKR, the high-virus phenotype of F/St was found to be recessive and was shown to be governed by a single locus, Cxv-1, less than 2 centimorgans from H-2K. The close association of Cxv-1 with the H-2 complex was confirmed by the observation that B10.F mice, congeneic for the H-2 region of F/St, expressed high levels of infectious X-MuLV and XenCSA, whereas C57BL/10 mice and other C57BL/10 H-2 congeneic strains did not. Studies of hybrid mice homozygous for Cxv-1s, but segregating for a chromosome 1 X-MuLV induction locus (V locus) of F/St, demonstrated that the high-virus phenotype of F/St was dependent on the interaction between Cxv-1 and the chromosome 1 V locus.

Unique features of retrovirus expression in F/St mice.

F/St mice are unique in producing high levels of both ecotropic and xenotropic murine leukemia virus. The high ecotropic virus phenotype is determined by three or more V (virus-inducing) loci. A single locus for inducibility of xenotropic murine leukemia virus was mapped to chromosome 1 close to, but possibly not allelic to, Bxv-1. Although the high ecotropic virus phenotype is phenotypically dominant, the high xenotropic virus phenotype was recessive in all crosses tested. Suppression of xenotropic murine leukemia virus is governed by a single gene which is not linked to the xenotropic V locus.

Outcome of influenza infection: effect of site of initial infection and heterotypic immunity.

An infection established throughout the total respiratory tract of mice with a highly lung adapted influenza virus (H0N1) led to death from viral pneumonia. The 50% lethal dose (LD(50)) was approximately the same as the 50% infectious dose (ID(50)). An infection with the same virus initiated in the nasal mucosa spread to the trachea and lungs over a 3- to 5-day period but was not lethal except at very high infecting doses. The LD(50) was 30,000 times the ID(50). Mice that had recovered from a prior infection with A/PC/73(H3N2) demonstrated enhanced recovery (heterotypic immunity) when challenged with A/PR/8/34(H0N1). Heterotypically immune mice infected while anesthetized with this potentially lethal virus stopped shedding virus from the nose, trachea, and lungs by day 7 and recovered. Heterotypically immune mice, infected awake, stopped shedding virus from the nose by day 5, and, in fact, the virus did not spread to the trachea or lungs. Thus, some of the variation in the severity of influenza infections may be explained by two factors: the site of initial infection and previous infection with heterotypic influenza virus.

Abrogation of resistance to severe mousepox in C57BL/6 mice infected with LP-BM5 murine leukemia viruses.

Strain C57BL/6 (B6) mice infected with LP-BM5 murine leukemia virus (MuLV) develop a disease which combines abnormal lymphoproliferation with profound immunosuppression and has many features in common with human acquired immunodeficiency syndrome induced by HTLV-III/LAV retroviruses. To determine whether this LP-BM5 MuLV infection would affect the innate resistance of B6 mice to a naturally occurring, highly virulent murine pathogen, mice were exposed to ectromelia virus at various times after treatment with LP-BM5 viruses. At week 4 after infection with LP-BM5, mice challenged with ectromelia virus were unable to generate a humoral immune response to this virus, and between weeks 8 and 10 after infection, challenged mice lost the ability to generate an ectromelia virus-specific cytotoxic-T-cell response. Loss of the cellular immune responses to ectromelia virus was associated with an increased susceptibility to the lethal effects of the virus.

Passive serum antibody causes temporary recovery from influenza virus infection of the nose, trachea and lung of nude mice.

BALB/c normal and nude mice were infected with a non-lethal mouse-passaged A/PC/1/73 (H3N2) influenza virus in order to assess the role of T cells on the course of disease of the nose, trachea and lung. The tracheal epithelium of both mouse strains was desquamated by 3 days after infection. Although normal regeneration began, nude mice never completed that regeneration whereas normal mice had fully regenerated tracheas by Day 14. This failure to complete the recovery was also evident from the continued virus shedding by the nude mouse. In order to assess the role of serum antibody on recovery from infection, ferret, goat or mouse antibody to H3N2 influenza virus was passively administered to nude mice after infection. It resulted in a transient decrease in virus shedding from the nose, trachea and lung, and complete but temporary regeneration of the tracheal epithelium. However, later in the course of the infection, when serum antibody levels were no longer detectable, the tracheal epithelium of these animals redesquamated and large amounts of virus were again shed from nose, trachea and lungs. We conclude that: (i) desquamation of the ciliated epithelium of the trachea is not T-cell dependent; and (ii) serum antibody can contribute to temporary recovery from infection, but by itself is insufficient for permanent recovery of the nose, trachea or lung.