Lung mucosa NK cells. NK cells found in the lung during the steady state exhibit a mature phenotype being in mice and CD16+ in humans suggesting that after development in the bone marrow immature (iNK, pink) and or mature (mNK, green) NK cells found in the blood home to the lung and may not require a specific signal or cell-cell interaction in a secondary lymphoid organ to migrate. Lung microbiome could impact NK cell development and/or function. During infection by a pathogen (red circle), dendritic cells in the lamina propria of the lung are triggered via pattern recognition receptors (PRRs) to produce inflammatory cytokines including IL-12 and IL-23. This in combination with recognition of infected cells by activating receptors (Ly49 mouse, KIR human, NKp both) on NK cells results in activation of resident NK cell populations to produce IFNγ, IL-17, and be cytolytic (CTL).
