Role of tumor necrosis factor-related apoptosis-inducing ligand in immune response to influenza virus infection in mice

Abstract

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of various tumor cells but not normal cells. However, various cytokines and virus infection differentially regulate TRAIL and TRAIL receptor expression. It has been demonstrated that virus infection changes the pattern of human TRAIL-receptor expression on normal cells, which were resistant to TRAIL-mediated apoptosis, and makes them susceptible to TRAIL-mediated apoptosis. Since previous studies on the function of TRAIL have been performed mainly in vitro, its physiological role in the immune response to virus infection remains unknown. In the present study, we investigated the expression of TRAIL in the lungs of influenza virus-infected mice and the function of TRAIL in the immune response to infection. Influenza virus infection increased TRAIL mRNA expression in the lung. TRAIL protein expression was induced on NK cells in the lung 4 days after infection. At 7 days after infection, TRAIL protein expression was also detected on CD4(+) and CD8(+) T cells. However, NK cells and T cells in the lungs of uninfected mice did not express a detectable level of TRAIL on their cell surfaces. DR5, which is a mouse TRAIL receptor, was also induced to express after virus infection. Expression of both TRAIL and DR5 mRNAs was reduced to normal level at 6 weeks after virus infection. Administration of anti-TRAIL monoclonal antibody, which blocks TRAIL without killing TRAIL-expressing cells, to mice during influenza virus infection significantly delayed virus clearance in the lung. These results suggest that TRAIL plays an important role in the immune response to virus infection.

FIG. 1.

RT-PCR analysis of TRAIL and DR5 mRNA expression in lungs of influenza virus-infected mice and uninfected mice. Mice were inoculated intranasally with 25 PFU of influenza virus. Lungs were excised 0, 4, 7, 14, 21, and 42 days after infection. RNAs were isolated from lungs of uninfected and influenza virus-infected mice. GAPDH-normalized TRAIL and DR5 mRNA abundances are shown.

FIG. 2.

Flow cytometric analysis of TRAIL expression on NK cells and T cells in lungs of influenza virus-infected mice and uninfected mice. Mice were inoculated intranasally with 25 PFU of influenza virus. Lungs were excised 4 and 7 days after infection. Mononuclear cells were isolated from the pooled lungs of three uninfected mice or three influenza virus-infected mice, and TRAIL expression was analyzed by flow cytometry. Dot plots were acquired by gating on lymphocytes at FSC-SSC and NK1.1⁺ or CD3⁺ cells. Data shown are cell surface expression of TRAIL on NK cells (upper panels) and CD3⁺ T cells (lower panels). The percentage of TRAIL-expressing cells in each gated population is indicated.

FIG. 3.

Flow cytometric analysis of TRAIL expression on CD8⁺ and CD4⁺ T cells in lungs of influenza virus-infected mice and uninfected mice. Mononuclear cells were isolated from the pooled lungs of three influenza virus-infected mice 7 days after infection, and TRAIL expression on T-cell subsets was analyzed by flow cytometry. Dot plots were acquired by gating on lymphocytes at FSC-SSC and CD8⁺ or CD4⁺ cells. The data shown are cell surface expression of TRAIL on CD8⁺ T cells (upper panels) and CD4⁺ T cells (lower panels). The percentage of TRAIL-expressing cells in each gated population is indicated.

FIG. 4.

Pulmonary virus titers in mice administered anti-TRAIL MAb or rat IgG during influenza virus infection. Mice were infected intranasally with 25 PFU of influenza virus and treated with anti-TRAIL MAb or rat IgG 4 h before infection and 2, 5, and 7 days after infection. Lungs were excised 4, 7, and 10 days after infection and homogenized, and the supernatants were diluted for virus titer analysis. Circles indicate virus titers in individual mice. The virus titers in 1/20 volume of lung homogenates of rat IgG-treated mice (open circles) and in those of anti-TRAIL MAb-treated mice (closed circles) are shown. Means ± standard deviations are shown to the right of circles belonging to each group. Statistical analysis was performed using the Mann-Whitney U test.