TRANSITIONAL DENDRITIC CELLS ARE DISTINCT FROM CONVENTIONAL DC2 PRECURSORS AND MEDIATE PRO-INFLAMMATORY ANTIVIRAL RESPONSES. TRANSITIONAL DENDRITIC CELLS ARE DISTINCT FROM CONVENTIONAL DC2 PRECURSORS AND MEDIATE PRO-INFLAMMATORY ANTIVIRAL RESPONSES

High-dimensional approaches revealed emerging heterogeneity within dendritic cells (DC), including a population of transitional DC (tDC) present in mouse and human. However, tDC origin and relationship to other DC subsets are not fully understood. Here, we show that tDC are distinct from other well-characterized DC and conventional DC precursors (pre-cDC). We demonstrate that tDC originate from bone marrow progenitors shared with plasmacytoid DC (pDC). In the periphery, tDC contribute to the pool of ESAM+ type 2 DC (DC2), and these DC2 harbor pDC-related developmental features. Different from pre-cDC, tDC have lower turnover, capture antigen, respond to stimuli, and activate antigen-specific naïve T cells, all characteristics of differentiated DC. Different from pDC, viral sensing by tDC results in IL-1b secretion and fatal immune pathology in a murine coronavirus model. Our findings suggest that tDC are a distinct pDC-related subset with a DC2 differentiation potential and unique pro-inflammatory function during viral infections. Overall design: Examination of immune cells in murine bone marrow and spleen. Cells were CD135 enriched and sorted for live cells. Cells were barcoded, pooled and run on 2 lanes. Sorted splenocytes were mixed 1:1 from 2 gates: CD3-/CD19-/NK1.1-/Ly6G- and CD3-/CD19-/NK1.1-/Ly6G-/Xcr1-/CD11blo to enrich for tDC. BM cells were gated as CD3-/CD19-/NK1.1-/Ly6G-. After sort, cells were counted and resuspended at a concentration of 600 cells per uL. Cells suspensions were processed for 10X Genomics.

高维度分析手段揭示了树突状细胞（dendritic cells, DC）内部存在新兴的细胞异质性，其中包含一类在小鼠与人体内均存在的过渡型树突状细胞（transitional DC, tDC）。然而，目前学界对于tDC的起源及其与其他DC亚群的关联尚未完全明晰。本研究证实，tDC与其他已得到充分鉴定的DC及常规树突状细胞前体（conventional DC precursors, pre-cDC）存在显著差异。我们证明，tDC起源于与浆细胞样树突状细胞（plasmacytoid DC, pDC）共享的骨髓祖细胞。在外周组织中，tDC参与构成ESAM阳性2型树突状细胞（ESAM+ type 2 DC, DC2）的细胞池，且此类DC2携带有pDC相关的发育特征。与pre-cDC不同，tDC的细胞周转率更低，能够捕获抗原、响应刺激并激活抗原特异性初始T细胞，上述均为分化成熟DC的典型特征。与pDC不同，在小鼠冠状病毒模型中，tDC的病毒感知活动可引发IL-1b分泌，并导致致死性免疫病理损伤。本研究结果表明，tDC是一类独立的、与pDC相关的DC亚群，具备DC2分化潜能，并在病毒感染过程中发挥独特的促炎功能。整体实验设计：对小鼠骨髓与脾脏中的免疫细胞开展检测。首先对细胞进行CD135富集，并分选活细胞；随后对细胞进行条码标记、混合后在2个测序泳道上完成上机测序。将分选的脾细胞按1:1比例混合自两个设门群：CD3-/CD19-/NK1.1-/Ly6G- 与 CD3-/CD19-/NK1.1-/Ly6G-/Xcr1-/CD11blo，以富集tDC。骨髓细胞的设门方案为CD3-/CD19-/NK1.1-/Ly6G-。分选完成后，对细胞进行计数并重悬至每微升600个细胞的浓度；随后将细胞悬液用于10X基因组学（10X Genomics）平台的单细胞测序。