In vivo blockade of gamma interferon affects the influenza virus-induced humoral and the focal cellular immune response in lung tissue

Influenza virus infection induces the local production of gamma interferon (IFN-gamma) by T cells and non-T cells in the respiratory tract. To elucidate the possible functions of this cytokine, the humoral and local cellular immune responses to influenza virus were studied in BALB/c mice with or without in vivo neutralization of IFN-gamma by using monoclonal antibodies, Neutralization of IFN-gamma led to a significant reduction in virus-specific titers of immunoglobulins G2a and G3 in serum but had little effect on other isotypes, Studies on cells isolated from the lung parenchyma itself revealed that at the height of the immune response the ability of these cells to produce cytokines after antigen or T-cell receptor/CD3 stimulation was not affected, Ex vivo cytolytic activity by lung parenchyma cells, which is induced by infection with this virus in normal mice, was also found to be undisturbed by this treatment, even though anti-IFN-gamma antibody activity was recovered from lung lavage samples and sera at all days studied, Surprisingly, in vivo neutralization of IFN-gamma led to a significant reduction in the magnitude of the cellular infiltrate in the lung tissue which followed infection, suggesting an involvement of IFN-gamma in the mechanisms that regulate increased leucocyte traffic in the inflamed lung parenchyma, This conclusion was supported by findings of differences between mock-treated and anti-IFN-gamma-treated mice in the number of CD8(+) lung T cells expressing CD49d (alpha 4-integrin) and CD62L at various times after influenza virus infection. This study therefore demonstrates that IFN-gamma affects the local cellular response in the respiratory tract as well as the systemic humoral response to influenza virus infection.