Nonplasmacytoid, high IFN-α-producing, bone marrow dendritic cells

The activation trajectory of plasmacytoid dendritic cells in vivo during a viral infection

Plasmacytoid dendritic cells (pDCs) are a major source of type I interferon (IFN-I). What other functions pDCs exert in vivo during viral infections is controversial, and more studies are needed to understand their orchestration. In the present study, we characterize in depth and link pDC activation states in animals infected by mouse cytomegalovirus by combining Ifnb1 reporter mice with flow cytometry, single-cell RNA sequencing, confocal microscopy and a cognate CD4 T cell activation assay. We show that IFN-I production and T cell activation were performed by the same pDC, but these occurred sequentially in time and in different micro-anatomical locations. In addition, we show that pDC commitment to IFN-I production was marked early on by their downregulation of leukemia inhibitory factor receptor and was promoted by cell-intrinsic tumor necrosis factor signaling. We propose a new model for how individual pDCs are endowed to exert different functions in vivo during a viral infection, in a manner tightly orchestrated in time and space.

Dendritic cell development: A personal historical perspective

Dendritic cells(DCs) were once considered as a single cell type closely related developmentally to macrophages. Now we recognise several subtypes of DCs and have outlined several different pathways that potentially lead to their development. This article outlines some of the research findings that led to these changes in perspective, from the point of view of one of the participants.

Different Life Cycle Stages of Plasmodium falciparum Induce Contrasting Responses in Dendritic Cells

Dendritic cells are key linkers of innate and adaptive immunity. Efficient dendritic cell activation is central to the acquisition of immunity and the efficacy of vaccines. Understanding how dendritic cells are affected by Plasmodium falciparum blood-stage parasites will help to understand how immunity is acquired and maintained, and how vaccine responses may be impacted by malaria infection or exposure. This study investigates the response of dendritic cells to two different life stages of the malaria parasite, parasitized red blood cells and merozoites, using a murine model. We demonstrate that the dendritic cell responses to merozoites are robust whereas dendritic cell activation, particularly CD40 and pro-inflammatory cytokine expression, is compromised in the presence of freshly isolated parasitized red blood cells. The mechanism of dendritic cell suppression by parasitized red blood cells is host red cell membrane-independent. Furthermore, we show that cryopreserved parasitized red blood cells have a substantially reduced capacity for dendritic cell activation.

Plasmacytoid dendritic cell heterogeneity is defined by CXCL10 expression following TLR7 stimulation

Plasmacytoid dendritic cells (pDCs) play a critical role in bridging the innate and adaptive immune systems. pDCs are specialized type I interferon (IFN) producers, which has implicated them as initiators of autoimmune pathogenesis. However, little is known about the downstream effectors of type I IFN signaling that amplify autoimmune responses. Here, we have used a chemokine reporter mouse to determine the CXCR3 ligand responses in DCs subsets. Following TLR7 stimulation, conventional type 1 and type 2 DCs (cDC1 and cDC2, respectively) uniformly upregulate CXCL10. By contrast, the proportion of chemokine positive pDCs was significantly less, and stable CXCL10⁺ and CXCL10^- populations could be distinguished. CXCL9 expression was induced in all cDC1s, in half of the cDC2 but not by pDCs. The requirement for IFNAR signaling for chemokine reporter expression was interrogated by receptor blocking and deficiency and shown to be critical for CXCR3 ligand expression in Flt3-ligand-derived DCs. Chemokine-producing potential was not concordant with the previously identified markers of pDC heterogeneity. Finally, we show that CXCL10⁺ and CXCL10^- populations are transcriptionally distinct, expressing unique transcriptional regulators, IFN signaling molecules, chemokines, cytokines, and cell surface markers. This work highlights CXCL10 as a downstream effector of type I IFN signaling and suggests a division of labor in pDCs subtypes that likely impacts their function as effectors of viral responses and as drivers of inflammation.

Dendritic cell subsets

Dendritic cells (DC) are professional antigen presenting cells comprising a variety of subsets, as either resident or migrating cells, in lymphoid and non-lymphoid organs. In the steady state DC continually process and present antigens on MHCI and MHCII, processes that are highly upregulated upon activation. By expressing differential sets of pattern recognition receptors different DC subsets are able to respond to a range of pathogenic and danger stimuli, enabling functional specialisation of the DC. The knowledge of functional specialisation of DC subsets is key to efficient priming of T cells, to the design of effective vaccine adjuvants and to understanding the role of different DC in health and disease. This review outlines mouse and human steady state DC subsets and key attributes that define their distinct functions.

African Swine Fever Virus Biology and Vaccine Approaches

African swine fever (ASF) is an acute and often fatal disease affecting domestic pigs and wild boar, with severe economic consequences for affected countries. ASF is endemic in sub-Saharan Africa and the island of Sardinia, Italy. Since 2007, the virus emerged in the republic of Georgia, and since then spread throughout the Caucasus region and Russia. Outbreaks have also been reported in Belarus, Ukraine, Lithuania, Latvia, Estonia, Romania, Moldova, Czech Republic, and Poland, threatening neighboring West European countries. The causative agent, the African swine fever virus (ASFV), is a large, enveloped, double-stranded DNA virus that enters the cell by macropinocytosis and a clathrin-dependent mechanism. African Swine Fever Virus is able to interfere with various cellular signaling pathways resulting in immunomodulation, thus making the development of an efficacious vaccine very challenging. Inactivated preparations of African Swine Fever Virus do not confer protection, and the role of antibodies in protection remains unclear. The use of live-attenuated vaccines, although rendering suitable levels of protection, presents difficulties due to safety and side effects in the vaccinated animals. Several African Swine Fever Virus proteins have been reported to induce neutralizing antibodies in immunized pigs, and vaccination strategies based on DNA vaccines and recombinant proteins have also been explored, however, without being very successful. The complexity of the virus particle and the ability of the virus to modulate host immune responses are most likely the reason for this failure. Furthermore, no permanent cell lines able to sustain productive virus infection by both virulent and naturally attenuated African Swine Fever Virus strains exist so far, thus impairing basic research and the commercial production of attenuated vaccine candidates.

Sensitivity of African swine fever virus to type I interferon is linked to genes within multigene families 360 and 505

African swine fever virus (ASFV) causes a lethal haemorrhagic disease of pigs. There are conflicting reports on the role of interferon in ASFV infection. We therefore analysed the interaction of ASFV with porcine interferon, in vivo and in vitro. Virulent ASFV induced biologically active IFN in the circulation of pigs from day 3-post infection, whereas low virulent OUR T88/3, which lacks genes from multigene family (MGF) 360 and MGF505, did not. Infection of porcine leucocytes enriched for dendritic cells, with ASFV, in vitro, induced high levels of interferon, suggesting a potential source of interferon in animals undergoing acute ASF. Replication of OUR T88/3, but not virulent viruses, was reduced in interferon pretreated macrophages and a recombinant virus lacking similar genes to those absent in OUR T88/3 was also inhibited. These findings suggest that as well as inhibiting the induction of interferon, MGF360 and MGF505 genes also enable ASFV to overcome the antiviral state.

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Virulent strains of African swine fever virus induces interferon during infection.

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Virulent, but not attenuated strains of ASFV are resistant to the antiviral effects of interferon in porcine macrophages.

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Sensitivity to interferon is linked to genes within multigene family 360 and multigene family 530.

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Dendritic cells are a potential source of the interferon detected in vivo.

Human dendritic cell subsets and function in health and disease

The method of choice for the development of new vaccines is to target distinct dendritic cell subsets with antigen in vivo and to harness their function in situ to enhance cell-mediated immunity or induce tolerance to specific antigens. The innate functions of dendritic cells themselves may also be targeted by inhibitors or activators that would target a specific function such as interferon production, potentially important in autoimmune disease and chronic viral infections. Importantly targeting dendritic cells requires detailed knowledge of both the surface phenotype and function of each dendritic cell subset, including how they may respond to different types of vaccine adjuvants, their ability to produce soluble mediators and to process and present antigens and induce priming of naïve T cells. This review summarizes our knowledge of the functional attributes of the human dendritic cell subsets in the steady state and upon activation and their roles in human disease.

The multifaceted biology of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a unique DC subset that specializes in the production of type I interferons (IFNs). pDCs promote antiviral immune responses and have been implicated in the pathogenesis of autoimmune diseases that are characterized by a type I IFN signature. However, pDCs can also induce tolerogenic immune responses. In this Review, we summarize recent progress in the field of pDC biology, focusing on the molecular mechanisms that regulate the development and functions of pDCs, the pathways involved in their sensing of pathogens and endogenous nucleic acids, their functions at mucosal sites, and their roles in infection, autoimmunity and cancer.

Stressful presentations: mild cold stress in laboratory mice influences phenotype of dendritic cells in naïve and tumor-bearing mice

The ability of dendritic cells (DCs) to stimulate and regulate T cells is critical to effective anti-tumor immunity. Therefore, it is important to fully recognize any inherent factors which may influence DC function under experimental conditions, especially in laboratory mice since they are used so heavily to model immune responses. The goals of this report are to 1) briefly summarize previous work revealing how DCs respond to various forms of physiological stress and 2) to present new data highlighting the potential for chronic mild cold stress inherent to mice housed at the required standard ambient temperatures to influence baseline DCs properties in naïve and tumor-bearing mice. As recent data from our group shows that CD8⁺ T cell function is significantly altered by chronic mild cold stress and since DC function is crucial for CD8⁺ T cell activation, we wondered whether housing temperature may also be influencing DC function. Here we report that there are several significant phenotypical and functional differences among DC subsets in naïve and tumor-bearing mice housed at either standard housing temperature or at a thermoneutral ambient temperature, which significantly reduces the extent of cold stress. The new data presented here strongly suggests that, by itself, the housing temperature of mice can affect fundamental properties and functions of DCs. Therefore differences in basal levels of stress due to housing should be taken into consideration when interpreting experiments designed to evaluate the impact of additional variables, including other stressors on DC function.