May 2018 | Volume 9 | Article 1046 1 ORIGINAL RESEARCH published: 16 May 2018 doi: 10.3389/fmmu.2018.01046 Frontiers in Immunology | www.frontiersin.org Edited by: Uday Kishore, Brunel University London, United Kingdom Reviewed by: Jiu-Yao Wang, National Cheng Kung University, Taiwan Lubna Kouser, Imperial College London, United Kingdom *Correspondence: Peter König koenig@anat.uni-luebeck.de † Shared frst authorship. ‡ Shared senior authorship. Specialty section: This article was submitted to Molecular Innate Immunity, a section of the journal Frontiers in Immunology Received: 17 December 2017 Accepted: 26 April 2018 Published: 16 May 2018 Citation: Hoffmann FM, Berger JL, Lingel I, Laumonnier Y, Lewkowich IP, Schmudde I and König P (2018) Distribution and Interaction of Murine Pulmonary Phagocytes in the Naive and Allergic Lung. Front. Immunol. 9:1046. doi: 10.3389/fmmu.2018.01046 Distribution and Interaction of Murine Pulmonary Phagocytes in the Naive and Allergic Lung Franziska M. Hoffmann 1,2† , Johann L. Berger 1,2† , Imke Lingel 1,2 , Yves Laumonnier 3 , Ian P. Lewkowich 4,5 , Inken Schmudde 1,2‡ and Peter König 1,2 * ‡ 1 Institute of Anatomy, University of Lübeck, Lübeck, Germany, 2 Airway Research Center North (ARCN), German Center for Lung Research (DZL), Lübeck, Germany, 3 Institute for Systemic Infammation Research, University of Lübeck, Lübeck, Germany, 4 Division of Immunobiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, United States, 5 Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States The division of labor between pulmonary phagocytic subsets [macrophage/monocyte and dendritic cell (DC) subpopulations] has been described at the functional level. However, whether these lung phagocytes also display unique spatial distribution remains unclear. Here, to analyze cellular distribution in lung compartments and contacts between phago- cyte subpopulations, we established an immunohistochemistry (IHC)-based method to clearly identify murine lung phagocyte subsets in situ based on differential expression of CD11c, CD11b, MHC-II, Langerin and mPDCA-1. Furthermore, we investigated sub- set-specifc functional differences in antigen uptake and spatial changes upon allergic sensitization. Our staining allowed the distinction between alveolar macrophages (AMs), interstitial macrophage (IM) subpopulations, CD11b + DC subpopulations, CD103 + DCs, and plasmacytoid DCs (pDCs). We identifed interstitial regions between airways and around airways as regions of IM/CD11b + DC/CD103 + DC clusters, where a subset of IMs (IM2) and CD103 + DCs formed intense contacts that decreased upon allergic sensitization. These data indicate functional interactions between both cell types either in steady state or after antigen encounter affecting the development of allergies or toler- ance. Furthermore, we observed major antigen uptake in AMs and IMs rather than DC subpopulations that was not restricted to airways and adjacent areas. This will enable to focus future studies to immunologically relevant cellular interactions and to unravel which cells are tipping the balance between pro-infammatory immune responses or tolerance. Keywords: dendritic cells, macrophages, lung, immunohistochemistry, spatial distribution, antigen uptake, allergic airway disease INTRODUCTION Te lung represents an interface between tissue and environment that continuously faces potential threats including inhaled airborne particles and pathogens. To prevent infammation, lung phagocytes constantly clear inhaled particles in a silent manner (1) and secrete mediators that activate resident immune cells, typically in a tolerogenic manner (2). However, under pathological circumstances, lung phagocytes contribute to infammatory immune responses against harmless allergens like pol- len and house dust mite (HDM) feces, leading to an allergic asthma reaction instead of tolerance (3). Terefore, in order to protect tissue homeostasis, the balance between pro- and anti-infammatory activities of lung phagocytes is tightly regulated. Although the precise factors responsible for promoting pro- and anti-infammatory responses remain incompletely understood, unique subsets of lung phagocytes including dendritic cells