Plasmacytoid dendritic cells (pDCs) are sensor cells with diverse immune functions, from type I interferon (IFN-I) production to antigen presentation, T cell activation, and tolerance. Regulation of ...these functions remains poorly understood but could be mediated by functionally specialized pDC subpopulations. We address pDC diversity using a high-dimensional single-cell approach: mass cytometry (CyTOF). Our analysis uncovers a murine pDC-like population that specializes in antigen presentation with limited capacity for IFN-I production. Using a multifaceted cross-species comparison, we show that this pDC-like population is the definitive murine equivalent of the recently described human AXL+ DCs, which we unify under the name transitional DCs (tDCs) given their continuum of pDC and cDC2 characteristics. tDCs share developmental traits with pDCs, as well as recruitment dynamics during viral infection. Altogether, we provide a framework for deciphering the function of pDCs and tDCs during diseases, which has the potential to open new avenues for therapeutic design.
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•We identify the murine homolog of human AXL+ DCs, now called transitional DCs (tDCs)•tDC development depends on Tcf4, similar to pDCs•tDCs are inefficient at IFN-I production but can efficiently activate T cells•During influenza infection, tDCs and pDCs accumulate in the lung
Dendritic cells (DCs) are unique therapeutic targets given their capacity to modulate immune responses. Yet complete alignment of the DC network between species is lacking. Using a multi-dimensional approach, Leylek et al. identify the mouse homolog of human AXL+ DCs, named transitional DCs (tDCs), and reveal their similarities with pDCs.
Class-switched antibodies to double-stranded DNA (dsDNA) are prevalent and pathogenic in systemic lupus erythematosus (SLE), yet mechanisms of their development remain poorly understood. Humans and ...mice lacking secreted DNase DNASE1L3 develop rapid anti-dsDNA antibody responses and SLE-like disease. We report that anti-DNA responses in Dnase1l3−/− mice require CD40L-mediated T cell help, but proceed independently of germinal center formation via short-lived antibody-forming cells (AFCs) localized to extrafollicular regions. Type I interferon (IFN-I) signaling and IFN-I-producing plasmacytoid dendritic cells (pDCs) facilitate the differentiation of DNA-reactive AFCs in vivo and in vitro and are required for downstream manifestations of autoimmunity. Moreover, the endosomal DNA sensor TLR9 promotes anti-dsDNA responses and SLE-like disease in Dnase1l3−/− mice redundantly with another nucleic acid-sensing receptor, TLR7. These results establish extrafollicular B cell differentiation into short-lived AFCs as a key mechanism of anti-DNA autoreactivity and reveal a major contribution of pDCs, endosomal Toll-like receptors (TLRs), and IFN-I to this pathway.
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•Anti-DNA antibody response is driven by T-dependent extrafollicular plasmablasts•IFN-I signaling propagates anti-DNA responses and SLE-like disease•IFN-I produced by pDCs promotes plasmablast proliferation and differentiation•TLR9 drives anti-DNA responses and autoimmunity redundantly with TLR7
Autoantibodies to self-DNA are a defining feature of systemic lupus erythematosus (SLE), yet the mechanisms of their development remain poorly understood. Soni et al. show that anti-DNA autoreactivity is driven by extrafollicular B cell differentiation into short-lived plasmablasts, which is facilitated by plasmacytoid dendritic cells, type I interferon, and endosomal Toll-like receptors 7 and 9.
Antibodies to double-stranded DNA (dsDNA) are prevalent in systemic lupus erythematosus (SLE), particularly in patients with lupus nephritis, yet the nature and regulation of antigenic cell-free DNA ...(cfDNA) are poorly understood. Null mutations in the secreted DNase DNASE1L3 cause human monogenic SLE with anti-dsDNA autoreactivity. We report that >50% of sporadic SLE patients with nephritis manifested reduced DNASE1L3 activity in circulation, which was associated with neutralizing autoantibodies to DNASE1L3. These patients had normal total plasma cfDNA levels but showed accumulation of cfDNA in circulating microparticles. Microparticle-associated cfDNA contained a higher fraction of longer polynucleosomal cfDNA fragments, which bound autoantibodies with higher affinity than mononucleosomal fragments. Autoantibodies to DNASE1L3-sensitive antigens on microparticles were prevalent in SLE nephritis patients and correlated with the accumulation of cfDNA in microparticles and with disease severity. DNASE1L3-sensitive antigens included DNA-associated proteins such as HMGB1. Our results reveal autoantibody-mediated impairment of DNASE1L3 activity as a common nongenetic mechanism facilitating anti-dsDNA autoreactivity in patients with severe sporadic SLE.
Tissue-resident macrophages are a diverse population of cells that perform specialized functions including sustaining tissue homeostasis and tissue surveillance. Here, we report an interstitial ...subset of CD169
lung-resident macrophages that are transcriptionally and developmentally distinct from alveolar macrophages (AMs). They are primarily localized around the airways and are found in close proximity to the sympathetic nerves in the bronchovascular bundle. These nerve- and airway-associated macrophages (NAMs) are tissue resident, yolk sac derived, self-renewing, and do not require CCR2
monocytes for development or maintenance. Unlike AMs, the development of NAMs requires CSF1 but not GM-CSF. Bulk population and single-cell transcriptome analysis indicated that NAMs are distinct from other lung-resident macrophage subsets and highly express immunoregulatory genes under steady-state and inflammatory conditions. NAMs proliferated robustly after influenza infection and activation with the TLR3 ligand poly(I:C), and in their absence, the inflammatory response was augmented, resulting in excessive production of inflammatory cytokines and innate immune cell infiltration. Overall, our study provides insights into a distinct subset of airway-associated pulmonary macrophages that function to maintain immune and tissue homeostasis.
An IRF8-dependent subset of conventional dendritic cells (cDCs), termed cDC1, effectively cross-primes CD8
T cells and facilitates tumor-specific T cell responses. Etv6 is an ETS family transcription ...factor that controls hematopoietic stem and progenitor cell (HSPC) function and thrombopoiesis. We report that like HSPCs, cDCs express Etv6, but not its antagonist, ETS1, whereas interferon-producing plasmacytoid dendritic cells (pDCs) express both factors. Deletion of Etv6 in the bone marrow impaired the generation of cDC1-like cells in vitro and abolished the expression of signature marker CD8α on cDC1 in vivo. Moreover, Etv6-deficient primary cDC1 showed a partial reduction of cDC-specific and cDC1-specific gene expression and chromatin signatures and an aberrant up-regulation of pDC-specific signatures. Accordingly, DC-specific Etv6 deletion impaired CD8
T cell cross-priming and the generation of tumor antigen-specific CD8
T cells. Thus, Etv6 optimizes the resolution of cDC1 and pDC expression programs and the functional fitness of cDC1, thereby facilitating T cell cross-priming and tumor-specific responses.
High-dimensional approaches have revealed heterogeneity amongst dendritic cells (DCs), including a population of transitional DCs (tDCs) in mice and humans. However, the origin and relationship of ...tDCs to other DC subsets has been unclear. Here we show that tDCs are distinct from other well-characterized DCs and conventional DC precursors (pre-cDCs). We demonstrate that tDCs originate from bone marrow progenitors shared with plasmacytoid DCs (pDCs). In the periphery, tDCs contribute to the pool of ESAM
type 2 DCs (DC2s), and these DC2s have pDC-related developmental features. Different from pre-cDCs, tDCs have less turnover, capture antigen, respond to stimuli and activate antigen-specific naïve T cells, all characteristics of differentiated DCs. Different from pDCs, viral sensing by tDCs results in IL-1β secretion and fatal immune pathology in a murine coronavirus model. Our findings suggest that tDCs are a distinct pDC-related subset with a DC2 differentiation potential and unique proinflammatory function during viral infections.
Plasmacytoid dendritic cells (pDCs) can rapidly produce interferons and other soluble factors in response to extracellular viruses or virus mimics such as CpG-containing DNA. pDCs can also recognize ...live cells infected with certain RNA viruses, but the relevance and functional consequences of such recognition remain unclear. We studied the response of primary DCs to the prototypical persistent DNA virus, human cytomegalovirus (CMV). Human pDCs produced high amounts of type I interferon (IFN-I) when incubated with live CMV-infected fibroblasts but not with free CMV; the response involved integrin-mediated adhesion, transfer of DNA-containing virions to pDCs, and the recognition of DNA through TLR9. Compared with transient polyfunctional responses to CpG or free influenza virus, pDC response to CMV-infected cells was long-lasting, dominated by the production of IFN-I and IFN-III, and lacked diversification into functionally distinct populations. Similarly, pDC activation by influenza-infected lung epithelial cells was highly efficient, prolonged, and dominated by interferon production. Prolonged pDC activation by CMV-infected cells facilitated the activation of natural killer cells critical for CMV control. Last, patients with CMV viremia harbored phenotypically activated pDCs and increased circulating IFN-I and IFN-III. Thus, recognition of live infected cells is a mechanism of virus detection by pDCs that elicits a unique antiviral immune response.
The presence of tumor-infiltrating CD8(+) T cells is associated with tumor regression and better prognosis. Cytomegalovirus (CMV) infection elicits a robust and long-lasting CD8(+) T-cell response, ...which makes CMV a potentially promising vaccine vector against cancer. In the current study, we used recombinant murine CMV (MCMV) strains as prophylactic and therapeutic vaccines in an aggressive B16 lung metastatic melanoma model. Immunization with MCMV-expressing ovalbumin (OVA) induced a potent OVA-specific CD8(+) T-cell response and was effective in protecting mice from OVA-expressing B16 melanoma in an antigen-dependent manner. We engineered MCMV to express a modified B16 melanoma antigen gp100 (MCMV-gp100KGP). Immunization with MCMV-gp100KGP was highly effective in overcoming immune tolerance to self-antigen and induced a strong, long-lasting gp100-specific CD8(+) T-cell response even in the presence of preexisting anti-CMV immunity. Furthermore, both prophylactic and therapeutic vaccinations of mice with MCMV-gp100KGP effectively protected mice from highly aggressive lung B16-F10 melanoma, and the protection was mediated by gp100-specific CD8(+) T cells. We showed that MCMV is a superior vaccine vector compared with a commonly used vesicular stomatitis virus vector. Collectively, our studies demonstrate that CMV is a promising vaccine vector to prevent and treat tumors.
Abstract
The spleen is an important site for generating protective immune responses against pathogens. Immune cells in the spleen undergo rapid reorganization to initiate and maintain local ...inflammatory responses against pathogens. How the spatial dynamics of cellular communication are regulated in the spleen after infection remains unclear. Respectively, CD169+ macrophages are a population of tissue resident macrophages that are positioned in the marginal zone to rapidly encounter invading pathogens. However, the role of splenic CD169+ macrophages during infections is not well understood. Here we show that splenic CD169+ macrophages serve as a primary cellular host to blood-borne bacteria Listeria monocytogens (Lm) and are also essential for the clearance of other bacterial and viral pathogens. In addition to controlling initial bacterial growth, CD169+ macrophages orchestrated a second phase of innate protection by mediating the transport of Lm to the splenic T cell zones and driving the subsequent reorganization of neutrophils, monocytes, and NK cells into hierarchical clusters. Specifically our study revealed that bacterial transport to the T cell zones was mediated by trans-infection of closely interacting CD8α+ DCs with Lm-infected CD169+ macrophages. Although, CD8α+ DCs are required for a productive Lm infection in the spleen, to our surprise mice that lacked both CD8α+ DCs and CD169+ macrophages were unable to control Lm infection. These results demonstrated that CD169+ macrophages regulated bacterial access to the pathogen favorable CD8α+ DC niche, ultimately providing a rationale for reassessing the current paradigm regarding the temporal role of CD8α+ DCs during Lm infection.
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