Interference with intraepithelial TNF-α signaling inhibits CD8(+) T-cell-mediated lung injury in influenza infection.

CD8(+) T-cell-mediated pulmonary immunopathology in respiratory virus infection is mediated in large part by antigen-specific TNF-α expression by antiviral effector T cells, which results in epithelial chemokine expression and inflammatory infiltration of the lung. To further define the signaling events leading to lung epithelial chemokine production in response to CD8(+) T-cell antigen recognition, we expressed the adenoviral 14.7K protein, a putative inhibitor of TNF-α signaling, in the distal lung epithelium, and analyzed the functional consequences. Distal airway epithelial expression of 14.7K resulted in a significant reduction in lung injury resulting from severe influenza pneumonia. In vitro analysis demonstrated a significant reduction in the expression of an important mediator of injury, CCL2, in response to CD8(+) T-cell recognition, or to TNF-α. The inhibitory effect of 14.7K on CCL2 expression resulted from attenuation of NF-κB activity, which was independent of Iκ-Bα degradation or nuclear translocation of the p65 subunit. Furthermore, epithelial 14.7K expression inhibited serine phosphorylation of Akt, GSK-3ß, and the p65 subunit of NF-κB, as well as recruitment of NF-κB for DNA binding in vivo. These results provide insight into the mechanism of 14.7K inhibition of NF-κB activity, as well as further elucidate the mechanisms involved in the induction of T-cell-mediated immunopathology in respiratory virus infection.

Lung epithelial NF-kappaB and Stat1 signaling in response to CD8+ T cell antigen recognition.

CD8+ T cell recognition of viral antigens presented by lung epithelial cells is important in the clearance of respiratory viral infection but may cause considerable injury to the lung. We have shown that a critical event of this type of injury is the activation of target epithelial cells and expression of chemokines by these cells. In this study, epithelial gene expression and transcription factor activation triggered by specific CD8+ T cell antigen recognition was examined in vitro and in vivo. T cell recognition triggers expression profiles of tumor necrosis factor-alpha (TNF-alpha)-dependent and interferon-gamma (IFN-gamma)-dependent genes in epithelial target cells. Consistent with these profiles, transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) were activated in lung epithelial cells of wild-type (WT) mice but not TNF receptor 1 (TNFR1)-deficient mice after CD8+ T cell recognition in vivo. In contrast, Stat1 activation and Stat1-dependent genes, such as IFN regulatory factor-1 (IRF-1) and guanylate-binding protein-2 (GBP-2), were induced to a similar extent in epithelial cells of both WT and TNFR1-deficient mice, indicating that this pathway is insufficient to induce pulmonary immunopathology in the absence of NF-kappaB-dependent transcriptional activation. Antibody neutralization of TNF-alpha abrogated epithelial monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) production in vitro as well as pulmonary immunopathology in vivo, confirming the primary importance of this cytokine in CD8+ T cell-mediated immunopathology.