Lymph node medulla is a quorum sensing niche for developing dendritic cells [preDC]

Conventional dendritic cells (cDC) and macrophages form complex networks that are essential for tissue homeostasis and immune defence. While the differentiation and residency of macrophages is regulated within distinct tissue niches, it is unclear whether DC development in tissues follows similar principles given their short life-span. By studying cDC development using fate mapping and depletion/reconstitution approaches, we found that preDC undergo distinct developmental stages. This development that preceded DC maturation was guided within the medullary cords of LNs. Intravital imaging and in situ photoconversion showed that preDC homed via medullary vessels and used them as guiding structures for their migration to the LN parenchyma. Infection-induced relocation of cDCs changed the availability of lymphocyte-derived Flt3l in the medulla which accelerated preDC development to ensure their local replenishment and responsiveness. Uncovering these principles of the spatiotemporal development of cDC and their complex cellular networks may guide novel angles for immunotherapy against cancer. Overall design: B6 wt mice were left untreated. Prtn3-Ert2Cre.lsl.tdTomato mice were treated either at day 3, 5 or 7 before organ harvest with tamoxifen. sdLN from all mice were isolated and digested with Collagenase D and DNase I. preDC were sorted based on CD11c, MHCII and CD135 expression using FACS AriaIII. The 4 different treatment conditions were stained with different antibody Hashtags before sorting and pooled for sequencing after the sort. Hashtag definitions: Hashtag1_TotalA0301: day 3 Hashtag2_TotalA0302: day 5 Hashtag3_TotalA0303: day 7 Hashtag4_TotalA0304: ctrl