A New Antigen-Uptaking Macrophage-Like Cell Population Contacts CD103+ Conventional Dendritic Cells around Airways

Primary data of DC localization in the lung is patchy. Because cell localization is directly linked to cell function, we aimed to localize DC and macrophage (MΦ) subtypes and determine the antigen-uptaking population by immunohistochemistry. Using an immunohistochemistry-optimized panel of markers we identified CD11b+ and CD103+ conventional (c)DCs, alveolar macrophages (AMΦs) plasmacytoid (p)DCs and monocytic (mo)DCs. We observed the accumulation of CD11b+ and CD103+ cDCs between the airway and pulmonary artery, but CD103+ cDCs were rarely found in the airway epithelium itself. Interestingly, around blood vessels and airways, CD103+ cDCs were often in close contact with a previously unrecognized CD11b+CD11c-MHC+ cell population, which resembles interstitial macrophages. To examine functional differences in pulmonary DC populations, antigen uptake was examined following administration of labeled ovalbumin (OVA) ex vivo. After OVA administration AMΦs were the main antigen-uptaking population in the lung. Interestingly, most of the OVA around the airways was taken up by the new interstitial macrophage like (IML) population. As a similar population has been described to induce tolerance in the gut via cross-talk with CD103+ cells, we speculate that our novel antigen-uptaking IML cell population may similarly regulate tolerance in the lung.