TNF/iNOS-producing dendritic cells are the necessary evil of lethal influenza virus infection.

Respiratory infection with highly pathogenic influenza A viruses is characterized by the exuberant production of cytokines and chemokines and the enhanced recruitment of innate inflammatory cells. Here, we show that challenging mice with virulent influenza A viruses, including currently circulating H5N1 strains, causes the increased selective accumulation of a particular dendritic cell subset, the tipDCs, in the pneumonic airways. These tipDCs are required for the further proliferation of influenza-specific CD8(+) T cells in the infected lung, because blocking their recruitment in CCR2(-/-) mice decreases the numbers of CD8(+) effectors and ultimately compromises virus clearance. However, diminution rather than total elimination of tipDC trafficking by treatment with the peroxisome proliferator-activated receptor-gamma agonist pioglitazone moderates the potentially lethal consequences of excessive tipDC recruitment without abrogating CD8(+) T cell expansion or compromising virus control. Targeting the tipDCs in this way thus offers possibilities for therapeutic intervention in the face of a catastrophic pandemic.