Cooperation between humoral factor(s) and Lyt-2+ T cells in effective clearance of Sendai virus from infected mouse lungs

The mechanism of cooperation between the L3T4+ and Lyt-2+ T cell subsets in effective clearance of Sendai virus from infected mouse lungs was studied by adoptive cell transfer using nude mice. Simultaneous transfer of a long-term-cultured Sendai virus-specific L3T4+ T cell line with L3T4+ cell-depleted immune spleen cell (L3T4-) fraction to infected nude mice could result in viral clearance, although single injection with either of these cells was not effective. Instead of the L3T4+ T cells, culture supernatants of the L3T4- T cell line or concanavalin A-stimulated mouse spleen cells and mouse serum immunized with the virus were also active in the cooperative viral clearance with L3T4- fraction. The role of the Sendai virus-sensitized L3T4- cell fraction in cooperative viral clearance with humoral factors could be replaced by neither T cell-deprived immune spleen cell fraction nor normal spleen cells. The 1,500 units of recombinant mouse interleukin 2 (IL-2), which was more than 12 times the IL-2 activity present in the supernatants of the T cell line or concanavalin A-stimulated spleen cells, failed to clear the virus in combination with the L3T4- fraction. Monoclonal antibodies to Sendai or mouse hepatitis viruses were also effective in the cooperative antiviral activity. IL-2 activity was not detected in these monoclonal antibodies and the mouse immune serum. Single injection of any humoral factors failed to clear the virus. These results indicate that Sendai virus-sensitized Lyt-2+ subset of T cells acts cooperatively with humoral factor(s) other than IL-2 or Sendai virus-specific antibody present in supernatants of the T cell line, of concanavalin A-stimulated spleen cells or hybridomas, and in mouse serum immunized with the virus.     

Tumorigenicity of persistently infected tumors in nude mice is a function of both virus and host cell type.

Although BHK-21 cells persistently infected with wild-type vesicular stomatitis virus (VSV) are sensitive to natural killer (NK) cells and do not form tumors in athymic nude mice, BHK-21 cells persistently infected with a previously isolated mutant virus (VSV-P) are resistant to NK cells and form tumors in nude mice. We used this VSV-P mutant to persistently infect HeLa cells and mouse tumor cell lines. A mouse mastocytoma line (P815) persistently infected with VSV-P was similar to BHK-21 cells in that it was resistant to NK cell lysis and formed tumors in nude mice. However, neither HeLa cells nor mouse myeloma lines persistently infected with VSV-P were resistant to NK cell lysis in vitro, and neither formed tumors in nude mice. Rejection by nude mice of HeLa cells and mouse myeloma cell lines persistently infected with VSV-P could be ablated by rabbit antiserum to asialo-GM1, implicating NK cells in the in vivo rejection of these persistently infected tumors. These results suggest that NK cell recognition and killing of virus-infected cells in vivo and in vitro depend upon genetic contributions from both the virus and the host cell.     

T cells subsets responsible for clearance of Sendai virus from infected mouse lungs

T cell subsets responsible for clearance of Sendai virus from mouse lungs determined by adoptive transfer of immune spleen cell fractions to infected nude mice. T cells with antiviral activity developed in spleens by 7 days after intranasal infection. Spleen cell fractions depleted of Lyt-2+, Lyt-1+, or L3T4+ cells showed antiviral activity in vivo, although the degree of the activity was lower than that of control whole spleen cells. The antiviral activity of the Lyt-2+ cell-depleted fraction was consistently higher than that of L3T4+ (Lyt-1+)-depleted cells. In vitro cytotoxic activity against Sendai virus-associated, syngeneic lipopolysaccharide-blast cells was detected in stimulated cells from intraperitoneally immunized mice but was lost after depletion of Lyt-2+ cells. Multiple injection of anti-Sendai virus antibody into infected nude mice had no effect on lung virus titer. These results indicate that L3T4+ (Lyt-1+) and Lyt-2+ subsets are cooperatively responsible for efficient clearance of Sendai virus from the mouse lung.     

Modification of immune response in nude mice infected with mouse hepatitis virus.

In nude mice experimentally infected with mouse hepatitis virus (MHV), the numbers of early and later plaque forming cells (PFC) to sheep red blood cells (SRBC) generated in the spleen were 7 to 20 times and 2 to 163 times, respectively, greater than those in non-infected nude mice, when SRBC were given at day 0 to day 21 postinfection. Splenic theta-positive lymphocytes in infected nude mice were shown to increase only at day 10 or more postinfection. PFC response to bacterial lipopolysaccharide, a T cell-independent antigen, was not modified in MHV-infected nude mice.     

Hypergammaglobulinemia in chickens congenitally infected with an avian leukosis virus.

Significantly elevated (2- to 5-fold higher than controls) serum levels of IgG were found in chickens congenitally infected with F42 strain of avian leukosis (ALV-F42) a subgroup A avian leukosis virus (ALV). A further increase in IgG levels in congenitally infected birds was found to be induced by injection of influenza virus in complete Freund's adjuvant(CFA). Serum immunoglobulin M (IgM) levels were not significantly elevated in ALV congenitally infected chickens except in those animals that had been injected with influenza virus in CFA. Hypergammaglobulinemia in ALV infected birds resulted only after congenital infection and not after infection of immunologically competent birds. Therefore this phenomenon appeared to have striking parallels with other persistent or chronic viral infections that have been previously described in mammals.     

Immunopathology of chronic progressive hepatitis in nude mice infected with low-virulent mouse hepatitis virus

Progressive hepatitis in athymic nude (nu/nu) mice due to a low-virulent mouse hepatitis virus, MHV-2 cc, was examined for involvement of immunocytes and serum antibodies. At 3 to 6 weeks postinoculation (p.i.) a considerable number of Mac 1- and asialo GM1-positive cells were accumulated in the affected liver and spleen. There were also some Thy-1-positive cells. Later than 2 weeks p.i., serum IgG and IgM antibodies were detected in parallel with virus-neutralizing activity, while the IgG levels were lower than those of infected euthymic (nu/+) littermates. By transfer of the infected nu/nu mouse serum, the recipient euthymic mice acquired resistance to lethal challenge infection with a virulent virus, MHV-2.     

Slow development of measles virus (Edmonston strain) infection in the brain of nude mice

The Edmonston strain of measles virus caused neurologic disease in athymic nude mice by intracerebral inoculation. The incubation periods of the disease, however, were extremely long, ranging from 59 to 140 days when the mice were inoculated with 10(4) plaque forming units (PFU) of the virus. The Edmonston strain was highly infectious in the nude mouse brain since virus infection was established even with 1 PFU of the virus. Virus titers in the brains of infected mice increased with the time of incubation. These results indicate that the extremely long incubation period of the disease is ascribed to very slow development of virus infection in the mouse brain. On the other hand, the incubation periods of the Biken strain of SSPE virus were very short (generally within 2 weeks) even with inoculations of 1 PFU of the virus. However, the extent of the dissemination of infection in brains was not significantly different between the two viruses as examined by immunofluorescent staining.     

Fatal pneumonia with terminal emaciation in nude mice caused by pneumonia virus of mice

Athymic nude mice used as sentinel animals in a mouse holding room died of pneumonia 17 to 32 weeks after being placed in the room. Lesions in the pulmonary parenchyma consisted of monocytic exudate, epithelial cell necrosis, hemorrhage, fibrin deposition and interstitial fibrosis. Septal edema, septal cell necrosis and septal capillary stasis were common, but there was limited sloughing of bronchial lining epithelium. Indirect fluorescence microscopy (IFA) of lung sections using pneumonia virus of mice (PVM) antibody was positive. The pneumonia and IFA results were reproduced in euthymic mice inoculated experimentally with lung suspension from naturally infected mice or with tissue culture fluid from cultures infected with American Type Culture Collection PVM. The lungs of a naturally infected nude mouse were studied by transmission electron microscopy. Virus growth was found on Type II alveolar epithelium and on poorly differentiated replacement alveolar epithelium. Virus particles appeared as long exophytic filaments containing one to six linearly arranged nucleocapsids. Inclusion bodies and intracellular virus structures were not observed.     

Survival of athymic (nu/nu) mice after Theiler''s murine encephalomyelitis virus infection by passive administration of neutralizing monoclonal antibody.

Little or no antiviral immune response is mounted in athymic nude mice infected with the Daniels strain of Theiler's murine encephalomyelitis virus. In these athymic mice, increasing levels of infectious virus could be detected in the central nervous system. Seventy-five percent (9 of 12) of the nude mice were moribund or dead by 4 weeks postinfection. In contrast, treatment of Theiler's virus-infected nude mice with a neutralizing monoclonal antibody (H7-2) against the viral protein VP-1 resulted in a dramatic reduction of infectious virus within the central nervous system. All antibody-treated nude animals survived beyond 4 weeks postinfection. Monoclonal antibody titers could be maintained by passive transfer in treated nude mice at levels comparable to those of polyclonal antibody titers found in heterozygous infected nu/+ littermates. Areas of demyelination were detected in the untreated animals as early as 7 days after infection with little or no remyelination present. In approximately one-half of the antibody-treated nude animals, no demyelinating lesions were found. However, the rest of these treated mice were found to have areas of both demyelination and remyelination. Thus, anti-Theiler's murine encephalomyelitis virus antibody against VP-1 can play a dramatic role in the survival of mice, clearance of virus, limiting viral spread, and altering the pattern of disease in the absence of a functional T-cell response.     

Studies of the susceptibility of nude, CD4 knockout, and SCID mutant mice to the disease induced by the murine AIDS defective virus.

Murine AIDS (MAIDS) is induced by a defective retrovirus that infects lymphocyte cells of the B lineage. To determine whether functional T cells are required for the infection of B cells, T-cell-deficient mice (nude, CD4 knockout, and SCII)) were infected with helper-free stocks of the MAIDS defective virus. Infection of B cells was monitored by Northern blot analysis and in situ hybridization. The C57BL/6 nude mice contained clusters of infected B cells, but less so than did the euthymic mice. In contrast, the (C57BL/6 x BALB/c)F1 nude mice harbored more infected B cells than did their euthymic littermates when maintained in a pathogen-free environment. Clusters of infected B cells were also detected in the MAIDS virus-infected CD4-/- knockout mice despite the total absence of CD4+ T cells in these mice. However, infected cells were not detected in SCID mice (deficient in mature T and B cells) inoculated with the same virus, indicating that precursor B cells are not a target of the virus in the absence of mature CD4+ T cells. These data confirm that the primary event in the development of MAIDS is the infection of relatively mature peripheral B cells and that CD4+ T cells are required to promote the expansion of these infected B cells.