Phagocytic CD206+ interstitial macrophages are remodeled after pneumococcal respiratory infection 2257592

Abstract Introduction Innate immune memory of lung macrophages is a crucial host safeguard against repeated respiratory infections. Based on the tissue compartments, there are alveolar macrophages and interstitial macrophages (IMs). IMs are further subdivided into CD206- and CD206+ subpopulations that have distinct localizations, transcriptomes, and functions. Whether IM subpopulations have the capacity to remodel after repeated infections is unknown. Methods Ontogeny of IMs was determined using Flk/switch reporter mice, whereby embryonic cells express tdTomato and bone marrow derived cells express GFP. Mice had left lobe intratracheal instillations of pneumococcus (“Experienced”) or saline (“Naïve”) at days 0 and 7. At day 35, IMs were studied using flow cytometry. Differences in localization were determined through mfIHC in Cx3cr1+/GFP reporter mice. IM recruitment was tested in B- and T-cell depleted mice (using cell-depleting antibodies against CD20 and CD4, respectively) and CCR2-/- mice. Transcriptomic analysis of lung macrophages was carried out by CITE scRNA-sequencing using surface protein markers to differentiate IM subsets. Phagocytic activity of IMs was determined by instilling fluorescent pneumococcus or E. coli Results The majority of IMs in the naïve lung are primarily bone marrow derived. Following repeated pneumococcus infections, both CD206- and CD206+ IMs were more abundant in experienced lungs compared to naïve lungs. Immunohistological staining showed IMs become the predominant lung macrophage in experienced mice. CD206+ IM recruitment was dependent on a second infection, and independent of B and T lymphocytes as well as CCR2. Only CD206+ IMs showed remodeled surface marker expression, transcriptome, and phagocytic capacity. Conclusion CD206+ IMs are phenotypically and functionally remolded after infection. Future mechanistic studies will evaluate how the enhanced phagocytic phenotype impacts host defense. Funding Source R01 Al115053, R35 HL135756, F31 HL178234 Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)