Novel features of the respiratory tract T-cell response to influenza virus infection: Lung T cells increase expression of gamma interferon mRNA in vivo and maintain high levels of mRNA expression for interleukin-5 (IL-5) and IL-10

Analysis of the respiratory tract before and after primary influenza virus infection revealed a virus-induced preferential accumulation of a CD8⁺ T-cell population that coexpresses mRNA for interleukin-5 (IL-5) and IL-10 with virus dose-dependent high levels of gamma interferon. However, cytokine production in lung tissues was not restricted to the T-cell population, since CD3^- cells were found to express mRNA for various cytokines, including IL-4 and particularly IL-6 and granulocyte-macrophage colony-stimulating factor. These data provide in vivo evidence for a local respiratory tract immune response to influenza virus infection dominated by cytokine-producing CD8⁺ T cells.