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This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various non-lymphoid tissues. Recent studies have provided evidence for an increasing number of phenotypically distinct conventional DC (cDC) subsets that on one hand exhibit a certain functional plasticity, but on the other hand are characterized by their tissue- and context-dependent functional specialization. Here, we describe a selection of assays for the functional characterization of mouse and human cDC. The first two protocols illustrate analysis of cDC endocytosis and metabolism, followed by guidelines for transcriptomic and proteomic characterization of cDC populations. Then, a larger group of assays describes the characterization of cDC migration in vitro, ex vivo, and in vivo. The final guidelines measure cDC inflammasome and antigen (cross)-presentation activity. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists., (© 2022 The Authors. European Journal of Immunology published by Wiley-VCH GmbH.)

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various non-lymphoid tissues. This article provides protocols with top ticks and pitfalls for preparation and successful generation of mouse and human DC from different cellular sources, such as murine BM and HoxB8 cells, as well as human CD34 + cells from cord blood, BM, and peripheral blood or peripheral blood monocytes. We describe murine cDC1, cDC2, and pDC generation with Flt3L and the generation of BM-derived DC with GM-CSF. Protocols for human DC generation focus on CD34 + cell culture on OP9 cell layers for cDC1, cDC2, cDC3, and pDC subset generation and DC generation from peripheral blood monocytes (MoDC). Additional protocols include enrichment of murine DC subsets, CRISPR/Cas9 editing, and clinical grade human DC generation. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists., (© 2022 The Authors. European Journal of Immunology published by Wiley-VCH GmbH.)

The CD11c + MHCII + compartment within GM-CSF cultures consists of a MHCII low CD11b high population (GM-Macs) and a MHCII high CD11b int population (GM-DCs), with different metabolic profiles. GM-Macs upregulate iNOS and produce nitric oxide (NO) upon TLR activation inhibiting mitochondrial respiration (OXPHOS) while promoting glycolytic metabolism in GM-DCs, which naturally do not express iNOS., (© 2022 The Authors. European Journal of Immunology published by Wiley-VCH GmbH.)

Upon antigen-specific or allogeneic activation, T cells sharply increase their metabolic activity to cope with augmented needs for proliferation and effector functions. Therefore, enzymes involved in energy metabolism constitute attractive targets to modulate the activity of pathogenic effector T cells in the setting of graft-versus-host-disease (GVHD). Here, we show that T cells deficient for acetyl-CoA carboxylase 1 (TACC1) are dramatically less pathogenic than wild-type (WT) T cells in a lethal C57BL/6 into BALB/c model of acute GVHD and permitted sustained survival of recipient mice. In line with this clinical observation, higher frequencies of GVHD-suppressing Foxp3(+) regulatory T (Treg) cells were detected in the colon of TACC T-cell recipients. In vitro, T-cell stimulation with allogeneic DCs induced higher proportions of Treg cells but also led to diminished proliferation of TACC1 T cells compared to WT T cells. Furthermore, TACC1 T cells activated by allogeneic DCs showed impaired glycolysis and lipid synthesis. Thus, targeting de novo fatty acid synthesis via acetyl-CoA carboxylase inhibition may be a promising new strategy to prevent GVHD., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dendritic cells (DCs) are key regulators of both innate and adaptive immunity. During infection, DCs recognise pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs) including the Toll-like receptor (TLR) family. TLRs mainly signal via the adaptor protein MyD88. This signalling pathway is required for immune protection during many infections, which are lethal in the absence of MyD88. However, the cell type specific importance of this pathway during both innate and adaptive immune responses against pathogens in vivo remains ill-defined. We discuss recent findings from conditional KO or gain-of-function mouse models targeting TLR/MyD88 signalling pathways in DCs and other myeloid cells during infection. While the general assumption that MyD88-dependent recognition by DCs is essential for inducing protective immunity holds true in some instances, the results surprisingly indicate a much more complex context-dependent requirement for this pathway in DCs and other myeloid or lymphoid cell-types in vivo. Furthermore, we highlight the advantages of Cre-mediated DC targeting approaches and their possible limitations. We also present future perspectives on the development of new genetic mouse models to target distinct DC subsets in vivo. Such models will serve to understand the functional heterogeneity of DCs in vivo., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Foxp3 specifies the Treg cell lineage and is indispensable for immune tolerance. Accordingly, rare Foxp3 mutations cause lethal autoimmunity. The mechanisms precipitating more prevalent human autoimmune diseases are poorly understood, but involve a combination of genetic and environmental factors. Many autoimmune diseases associate with a partial Treg-cell dysfunction, yet mouse models reflecting such complex pathophysiological processes are rare. Around 95% of Foxp3(+) Treg cells can be specifically depleted in bacterial artifical chromosome (BAC)-transgenic Depletion of REGulatory T cells (DEREG) mice through diphtheria toxin (DT) treatment. However, Treg-cell depletion fails to cause autoimmunity in adult DEREG mice for unclear reasons. By crossing Foxp3(GFP) knock-in mice to DEREG mice, we introduced additional genetic susceptibility that does not affect untreated mice. Strikingly, DT treatment of DEREG × Foxp3(GFP) mice rapidly causes autoimmunity characterized by blepharitis, tissue damage, and autoantibody production. This inflammatory disease is associated with augmented T-cell activation, increased Th2 cytokine production and myeloproliferation, and is caused by defective Treg-cell homeostasis, preventing few DT-insensitive Treg cells from repopulating the niche after Treg-cell depletion. Our study provides important insights into self-tolerance. We further highlight DEREG × Foxp3(GFP) mice as a model to investigate the role of environmental factors in precipitating autoimmunity. This may help to better understand and treat human autoimmunity., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Tuberculosis is a chronic infectious disease caused by Mycobacterium tuberculosis that is responsible for almost 1.5 million deaths per year. Sensing of mycobacteria by the host's immune system relies on different families of receptors present on innate immune cells. Amongst them, several members of the TLR family are involved in the activation of immune cells by mycobacteria, yet the in vivo contribution of individual TLRs to the protective immune response remains controversial. On the contrary, MyD88, the adaptor molecule for most TLRs, plays a non-redundant role in the protection against tuberculosis and mice with a complete germline deletion of MyD88 succumb very early to infection. MyD88 is expressed in both immune and non-immune cells, but it is not clear whether control of mycobacteria requires ubiquitous or cell-type specific MyD88 expression. Therefore, using novel conditional switch-on mouse models, we aimed to investigate the importance of MyD88 signalling in DCs and macrophages for the induction of protective effector mechanisms against mycobacterial infection. We conclude that specific reactivation of MyD88 signalling in CD11c- or lysozyme M-expressing myeloid cells during Mycobacterium bovis Bacille Calmette-Guerin infection is sufficient to restore systemic and local inflammatory cytokine production and to control pathogen burden., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Vaccination is one of the oldest yet still most effective methods to prevent infectious diseases. However, eradication of intracellular pathogens and treatment of certain diseases like cancer requiring efficient cytotoxic immune responses remain a medical challenge. In mice, a successful approach to induce strong cytotoxic CD8⁺ T-cell (CTL) reactions is to target antigens to DCs using specific antibodies against surface receptors in combination with adjuvants. A major drawback for translating this strategy into one for the clinic is the lack of analogous targets in human DCs. DC-SIGN (DC-specific-ICAM3-grabbing-nonintegrin/CD209) is a C-type lectin receptor with potent endocytic capacity and a highly restricted expression on human immature DCs. Therefore, DC-SIGN represents an ideal candidate for DC targeting. Using transgenic mice that express human DC-SIGN under the control of the murine CD11c promoter (hSIGN mice), we explored the efficacy of anti-DC-SIGN antibodies to target antigens to DCs and induce protective immune responses in vivo. We show that anti-DC-SIGN antibodies conjugated to OVA induced strong and persistent antigen-specific CD4⁺ and CD8⁺ T-cell responses, which efficiently protected from infection with OVA-expressing Listeria monocytogenes. Thus, we propose DC targeting via DC-SIGN as a promising strategy for novel vaccination protocols against intracellular pathogens., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

PI3Ks control signal transduction triggered by growth factors and G-protein-coupled receptors and regulate an array of biological processes, including cellular proliferation, differentiation, survival and migration. Herein, we investigated the role of PI3Kγ in the pathogenesis of EAE. We show that, in the absence of PI3Kγ expression, clinical signs of EAE were delayed and mitigated. PI3Kγ-deficient myelin oligodendrocyte glycoprotein (MOG)(35-55) -specific CD4(+) T cells appeared later in the secondary lymphoid organs and in the CNS than their WT counterparts. Transfer of WT CD4(+) cells into PI3Kγ(-/-) mice prior to MOG(35-55) immunisation restored EAE severity to WT levels, supporting the relevance of PI3Kγ expression in Th cells for the pathogenesis of EAE; however, PI3Kγ was dispensable for Th1 and Th17 differentiation, thus excluding an altered expression of these pathogenetically relevant cytokines as the cause for ameliorated EAE in PI3Kγ(-/-) mice. These findings demonstrate that PI3Kγ contributes to the development of autoimmune CNS inflammation., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)