SummaryDendritic cells (DCs) are professional antigen-presenting cells that hold great therapeutic potential. Multiple DC subsets have been described, and it remains challenging to align them across tissues and species to analyze their function in the absence of macrophage contamination. Here, we provide and validate a universal toolbox for the automated identification of DCs through unsupervised analysis of conventional flow cytometry and mass cytometry data obtained from multiple mouse, macaque, and human tissues. The use of a minimal set of lineage-imprinted markers was sufficient to subdivide DCs into conventional type 1 (cDC1s), conventional type 2 (cDC2s), and plasmacytoid DCs (pDCs) across tissues and species. This way, a large number of additional markers can still be used to further characterize the heterogeneity of DCs across tissues and during inflammation. This framework represents the way forward to a universal, high-throughput, and standardized analysis of DC populations from mutant mice and human patients.

Dendritic cells (DCs) and monocyte-derived macrophages (M s) are key components of intestinal immunity. However, the lack of surface markers differentiating M s from DCs has hampered understanding of their respective functions. Here, we demonstrate that, using CD64 expression, M s can be distinguished from DCs in the intestine of both mice and humans. On that basis, we revisit the phenotype of intestinal DCs in the absence of contaminating M s and we delineate a developmental pathway in the healthy intestine that leads from newly extravasated Ly-6C hi monocytes to intestinal M s. We determine how inflammation impacts this pathway and show that T cell-mediated colitis is associated with massive recruitment of monocytes to the intestine and the mesenteric lymph node (MLN). There, these monocytes differentiate into inflammatory M s endowed with phagocytic activity and the ability to produce inducible nitric oxide synthase. Eur. J. Immunol. 2012. 42: 3150-3166 HIGHLIGHTS 3151 IntroductionThe intestinal lamina propria (LP) contains cells that express high levels of CX 3 CR1, the receptor for the fractalkine chemokine [1,2]. Based on their monocytic origin and on their inability to migrate to the mesenteric lymph nodes (MLNs) such CX 3 CR1 hi cells have been defined as macrophages (M s) [1][2][3]. CX 3 CR1 hi M s contribute to the intestinal LP homeostasis through the production of anti-inflammatory cytokines and the clearance of commensal bacteria that breach the epithelial barrier [4]. In contrast, during intestinal inflammation, microenvironmental signals promote the differentiation of extravasated monocytes into proinflammatory M s with the ability to produce interleukin (IL)-12, IL-23, tumor necrosis (TNF)-α and inducible nitric oxide synthase (iNOS) [5][6][7]. However, little is known about the developmental trajectories that lead extravasated monocytes to either antior proinflammatory intestinal M s. This is primarily due to the fact that a surface marker permitting unequivocal identification of M s within the intestine and their distinction from dendritic cells (DCs) is lacking. The interstitial DCs (Int-DCs) present throughout the LP derive from blood precursors known as pre-DCs [2]. Under steady-state conditions, the Int-DCs found in the intestinal LP induce oral tolerance by carrying antigens originating from food or from harmless bacteria to the MLNs [8,9]. The CD103 + Int-DCs found in the steady-state LP have the selective ability to express aldehyde dehydrogenase (ALDH) and thereby produce retinoic acid (RA). As a result, upon migration to MLNs they trigger the differentiation of naive CD4 + T cells specific for food and microbiota antigens into induced Foxp3 + regulatory T (iTreg) cells [10][11][12][13]. In contrast, the Int-DCs that develop in inflamed LP upon exposure to pathogens lose their capacity to generate iTreg cells and, upon migration to the MLNs, trigger the differentiation of naive, antigen-responsive CD4 + T cells into T helper type 1 (Th1) cells that are specific for the invading patho...

Highlights d Type I interferon drives differentiation of inf-cDC2s that closely resemble MCs d Inf-cDC2s prime CD4 + and CD8 + T cells, whereas MCs lack APC function d Inf-cDC2s internalize antibody-complexed antigen via Fc receptors d IRF8 controls maturation gene module in inf-cDC2s