Lung dendritic cells migrate to the spleen to prime long-lived TCF1 memory CD8 T cell precursors after influenza infection.

CD8 T cell responses to pulmonary challenges are primed by lung migratory dendritic cells (mDCs), which capture antigens in the lungs and migrate to the lung-draining mediastinal lymph node (med-LN) to activate T cells. The lungs and the spleen are not connected by the lymphatic vasculature. Thus, the current paradigm suggests that, in response to respiratory virus infections that are restricted to the respiratory tract, priming of T cell responses by lung mDCs takes place entirely in the med-LN. Our results challenge this “LN-centric” paradigm by demonstrating that, during influenza virus infection, lung mDCs egress the med-LN and traffic to the spleen, where they prime influenza-specific CD8 T cells. CD8 T cells primed in the spleen are transcriptionally distinct and have enhanced ability to differentiate into long-lived memory cells compared with med-LN–primed counterparts. Thus, our data identify a lung mDC trafficking pathway that connects the lungs with the spleen.