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

Impaired CD8(+) T cell immunity after allogeneic bone marrow transplantation leads to persistent and severe respiratory viral infection

RATIONALE

Bone marrow transplant (BMT) recipients experience frequent and severe respiratory viral infections (RVIs). However, the immunological mechanisms predisposing to RVIs are uncertain. Therefore, we hypothesized that antiviral T cell immunity is impaired as a consequence of allogeneic BMT, independent of pharmacologic immunosuppression, and is responsible for increased susceptibility to RVI.

METHODS

Bone marrow and splenocytes from C57BL/6(H2(b)) mice were transplanted into B10.BR(H2(k)) (Allo) or C57BL/6(H2(b)) (Syn) recipients. Five weeks after transplantation, recipient mice were inoculated intranasally with mouse parainfluenza virus type 1 (mPIV-1), commonly known as Sendai virus (SeV), and monitored for relevant immunological and disease endpoints.

MAIN RESULTS

Severe and persistent airway inflammation, epithelial injury, and enhanced mortality are found after viral infection in Allo mice but not in control Syn and non-transplanted mice. In addition, viral clearance is delayed in Allo mice as evidenced by prolonged detection of viral transcripts at Day 15 post-inoculation (p.i.) but not in control mice. In concert with these events, we also detected decreased levels of total and virus-specific CD8(+) T cells, as well as increased T cellexpression of inhibitory receptor programmed death-1 (PD-1), in the lungs of Allo mice at Day 8 p.i. Adoptive transfer of CD8(+) T cells from non-transplanted mice recovered from SeV infection into Allo mice at Day 8 p.i. restored normal levels of viral clearance, epithelial repair, and lung inflammation.

CONCLUSIONS

Taken together these results indicate that allogeneic BMT results in more severe RVI based on the failure to develop an appropriate pulmonary CD8(+) T cell response, providing an important potential mechanism to target in improving outcomes of RVI after BMT.

Granzyme B regulates antiviral CD8+ T cell responses

CTLs and NK cells use the perforin/granzyme cytotoxic pathway to kill virally infected cells and tumors. Human regulatory T cells also express functional granzymes and perforin and can induce autologous target cell death in vitro. Perforin-deficient mice die of excessive immune responses after viral challenges, implicating a potential role for this pathway in immune regulation. To further investigate the role of granzyme B in immune regulation in response to viral infections, we characterized the immune response in wild-type, granzyme B-deficient, and perforin-deficient mice infected with Sendai virus. Interestingly, granzyme B-deficient mice, and to a lesser extent perforin-deficient mice, exhibited a significant increase in the number of Ag-specific CD8(+) T cells in the lungs and draining lymph nodes of virally infected animals. This increase was not the result of failure in viral clearance because viral titers in granzyme B-deficient mice were similar to wild-type mice and significantly less than perforin-deficient mice. Regulatory T cells from WT mice expressed high levels of granzyme B in response to infection, and depletion of regulatory T cells from these mice resulted in an increase in the number of Ag-specific CD8(+) T cells, similar to that observed in granzyme B-deficient mice. Furthermore, granzyme B-deficient regulatory T cells displayed defective suppression of CD8(+) T cell proliferation in vitro. Taken together, these results suggest a role for granzyme B in the regulatory T cell compartment in immune regulation to viral infections.

Protective effect of passive immunization against TNF-alpha in mice infected with Sendai virus

TNF-alpha has been reported to be induced in mice infected with Sendai virus. We evaluated the role of TNF-alpha in the virus infection. TNF-alpha was induced locally in proportion to virus titers in the lung. The activity was correlated with suppression of body weight gain. Passive immunization against TNF-alpha improved body weight gain and ameliorated pneumonic lesions in infected mice, and prevented them from lethal infection, but lung virus induced emaciation, pneumonic lesions and death were mediated by TNF-alpha.

Virus-induced increases in airway mast cells in brown Norway rats are associated with enhanced pulmonary viral replication and persisting lymphocytic infiltration

Brown Norway (BN) rats are more susceptible than Fischer 344 (F344) rats to parainfluenza virus-induced lung injury and to bronchiolar mast cell increases that are associated with persistent airway hyperresponsiveness. In this study, pulmonary viral replication as well as immune, inflammatory, and airway mast cell responses to Sendai virus infection were compared between neonatal BN and F344 rats. BN rats supported prolonged viral replication, and viral titers in BN rats were 5-fold higher (p < .05) than in F344 rats at 7 days after inoculation. F344 rats had 18-fold higher (p < .06) numbers of lymphocytes in bronchoalveolar lavage fluid at 7 days after inoculation than did BN rats. Persisting bronchiolar aggregates of lymphocytes, plasma cells, and macrophages were more common, and increases in bronchiolar mast cells were greater in BN rats than in F344 rats. No strain differences were detected in bronchiolar intramural infiltrates of CD4 + or CD8 + cells. The greater susceptibility of BN rats to virus-induced increases in bronchiolar mast cells and airway responsiveness may be the result of their less efficient viral clearance mechanisms and more persistent bronchiole-centered inflammatory response.

Induction of cytokines in mice with parainfluenza pneumonia

The possible involvement of cytokines in the acute viral pneumonia induced by the murine parainfluenza type 1 virus, Sendai virus, was studied. Cytokine profiles for both the respiratory tract and the draining mediastinal lymph node (MLN) of virus-infected C57BL/6J mice were quantified by using the single-cell cytokine (ELISPOT) assay with freshly isolated cell populations and enzyme-linked immunosorbent assay for lung lavage fluids and culture supernatants. Maximal levels of interleukin 2 (IL-2), gamma interferon (IFN-gamma), tumor necrosis factor, IL-6, and IL-10 were detected at the inflammatory site 7 to 10 days after infection, about the time that virus is cleared from the lung. The frequencies of cells producing IL-2, IL-4, IL-6, IL-10, IFN-gamma, and tumor necrosis factor were much higher for the bronchoalveolar lavage (BAL) cell population than for the MLN cell population. Cytokine production after in vitro restimulation of MLN cells was dominated by IL-2 and IFN-gamma, with low levels of IL-10 and IL-6 also being present. Most of the cytokine was produced by the CD4+ cells, although the CD8+ subset was also involved. No IL-4 was found in the BAL fluid or in culture supernatants from restimulated BAL or MLN cells, although a high frequency of IL-4-producing cells was demonstrated in the BAL population by ELISPOT analysis.

Analysis of the primary T-cell response to Sendai virus infection in C57BL/6 mice: CD4+ T-cell recognition is directed predominantly to the hemagglutinin-neuraminidase glycoprotein

Sendai virus infection of C57BL/6 mice elicits a strong CD4+ and CD8+ T-cell response in the respiratory tract. To investigate the specificity of the CD4+ T-cell response, a panel of hybridomas was generated from cells recovered from the respiratory tracts of infected mice. Using vaccinia virus recombinants expressing individual Sendai virus proteins, we found that the majority of these hybridomas (34 of 37) were specific for the hemagglutinin-neuraminidase (HN) glycoprotein. The hybridomas were then analyzed for reactivity to a set of overlapping peptides spanning the entire length of the hemagglutinin-neuraminidase glycoprotein. At least five H-2 I-Ab-restricted epitopes were defined in HN. The strong bias toward recognition of class II epitopes derived from a single viral protein contrasts with T-cell recognition of epitopes of several proteins in influenza A virus as found previously by others.

Cell-to-cell contact not soluble factors mediate suppression of lymphocyte proliferation by bovine parainfluenza virus type 3

We have previously characterized the ability of parainfluenza virus type 3-infected (PIV-3) and noninfected bovine alveolar macrophages (BAM) to support lymphocyte proliferation. While uninfected macrophages support proliferation of lymphocytes stimulated with concanavalin A (Con A), ovalbumin, and interleukin 2 (IL-2), lymphocyte [3H]thymidine incorporation was suppressed in the presence of PIV-3-infected BAM. Since viral infection of macrophages has been shown to alter arachidonic acid metabolism and cytokine secretion, we have determined if arachidonate metabolism or the lack of IL-1 and IL-2 mediated the suppression of lymphocyte proliferation by PIV-3. Inhibition of arachidonic acid metabolism failed to reverse the suppressive effect of viral infection as did supplementation of cultures with bovine recombinant IL-1 beta, IL-2, or lymphocyte-conditioned medium. Further, lymphocytes proliferated normally when physically separated from virus infected BAM by a semipermeable membrane. Stimulation of lymphocytes in contact with infected BAM resulted in marked suppression of lymphocyte [3H]thymidine incorporation. Interactions between stimulated lymphocytes and PIV-3-infected BAM resulted in PIV-3 infection of lymphocytes. Virus infection of lymphocytes was confirmed ultrastructurally by the presence of characteristic parainfluenza virus inclusions and virus budding from lymphocyte plasma membranes. It was concluded that suppression of lymphocyte proliferation by PIV-3 is mediated in part by infection of stimulated lymphocytes during cell-to-cell contact with BAM.

Brown Norway rats are high responders to bronchiolitis, pneumonia, and bronchiolar mastocytosis induced by parainfluenza virus

The pathogenesis of parainfluenza 1 (Sendai) virus infection was compared among 25-day-old BN, F344, and LEW rats to identify a sensitive as well as a resistant inbred rat strain to Sendai virus-induced lung injury during early life. At 7 days after inoculation, BN rats had 65-fold higher (P less than .001) pulmonary viral titers and threefold higher (P less than .002) numbers of neutrophils in bronchoalveolar lavage fluid than did F344 rats. At 14 days after inoculation, when most virus-induced inflammation had been resolved, BN rats had a threefold greater (P less than .01) incidence of bronchioles with aggregates of lymphocytes and macrophages than did F344 rats. Control BN rats had higher numbers of bronchiolar eosinophils than did F344 or LEW rats. Although viral inoculation resulted in increased numbers of bronchiolar mast cells in all three strains at 14 days, bronchiolar mast cell density was greater (P less than .005) in virus-inoculated BN and LEW rats than in F344 rats. We conclude that BN rats are high responders and F344 rats are low responders to Sendai virus-induced bronchiolitis, pneumonia, and airway mastocytosis. These strain differences may be useful in elucidating important pathogenetic mechanisms in virus-induced airway injury and mastocytosis.

Sendai virus infection of normal and protein malnourished mice: response of airway leukocytes to infection

We examined the cells recovered by bronchoalveolar lavage (BAL) during the course of respiratory infection caused by Sendai virus in normal (20% protein diet) and malnourished (2% protein diet) mice. As in our previous experiments, mortality in normal mice was 32% in comparison with 87% in the malnourished group. Virus was isolated until the 5th day in normally fed mice and until the 9th day in the malnourished group. BAL fluids contained 97% macrophages before infection in both groups. During infection there was a progressive lymphocyte response, reaching a peak of 60-70% on day 5 in the normal mice and on days 7-9 in the malnourished group. Subtyping of BAL cells by flow cytometry indicated that in uninfected animals lymphocytes were largely CD4-bearing. On days 3 and 5 post-infection most mononuclear cells were Thy 1.2-positive, but lacked both CD4 and CD8 markers and were therefore probably natural killer cells. Beginning on day 5, in both diet groups CD8-positive cells rose to become the predominant subset. In the 20% protein diet group, CD8-positive cells reached a maximum of 60% on day 7, whereas in the 2% protein diet group this level was not reached until day 9. These results were consistent in three separate experiments. In malnourished mice the delayed appearance of CD8-bearing cells in the airway may contribute to the higher mortality and delayed virus clearance during Sendai virus infection.

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.

Comparison of protective effects of serum antibody on respiratory and systemic infection of Sendai virus in mice

The protective effects of the passive administration of convalescent serum from mice infected with Sendai virus were evaluated in mice challenged intranasally with wild-type and a pantropic variant (F1-R) of Sendai virus. Adoptive transfer of the serum efficiently prevented F1-R from infecting the systemic organs, but it failed to protect the mice from infections of the respiratory tracts by either virus. Virus replication in nasal turbinates was not diminished while infection in the lung was suppressed sufficiently for the infected mice to survive the infection. These findings suggest that serum antibody is less effective for the protection against viral infections on the surface of the respiratory tract, but it is effective for inhibition of spread of the virus into the systemic organs.