Batf3-dependent orchestration of the robust Th1 responses and fungal control during cryptococcal infection, the role of cDC1

While type I conventional dendritic cells (cDC1s) are vital for generating adaptive immunity against intracellular pathogens and tumors, their role in defense against fungal pathogen Cryptococcus neoformans remains unclear. We investigated the role of the cDC1 subset in a fungus-restricting mouse model of cryptococcal infection. The cDC1 subset displayed a unique transcriptional signature with highly upregulated T-cell recruitment, polarization, and activation pathways compared to other DC subsets. Using Batf3-/- mice, which lack the cDC1 population, our results support that Batf3-dependent cDC1s are pivotal for the development of the effective immune response against cryptococcal infection, particularly within the lung and brain. Deficiency in Batf3 cDC1 led to diminished CD4 accumulation and decreased IFNγ production across multiple organs, supporting that cDC1s are a major driver of potent Th1 responses during cryptococcal infection. Consistently, mice lacking Batf3-cDC1 demonstrated markedly diminished fungicidal activity and weaker containment of the fungal pathogen. In conclusion, Batf3-dependent cDC1 can function as a linchpin in mounting Th1 response, ensuring effective fungal control during cryptococcal infection. Harnessing cDC1 pathways may present a promising strategy for interventions against this pathogen.IMPORTANCECryptococcus neoformans causes severe meningoencephalitis, accounting for an estimated 200,000 deaths each year. Central to mounting an effective defense against these infections is T-cell-mediated immunity, which is orchestrated by dendritic cells (DCs). The knowledge about the role of specific DC subsets in shaping anti-cryptococcal immunity is limited. Here, we demonstrate that Batf3 cDC1s are important drivers of protective Th1 CD4 T-cell responses required for clearance of cryptococcal infection. Deficiency of Batf3 cDC1 in the infected mice leads to significantly reduced Th1 response and exacerbated fungal growth to the point where depleting the remaining CD4 T cells no longer affects fungal burden. Unveiling this pivotal role of cDC1 in antifungal defense is likely to be important for the development of vaccines and therapies against life-threatening fungal pathogens.

Resistance to Experimental Visceral Leishmaniasis in Mice Infected With Leishmania infantum Requires Batf3

Unveiling the protective immune response to visceral leishmaniasis is critical for a rational design of vaccines aimed at reducing the impact caused by this fatal, if left untreated, vector-borne disease. In this study we sought to determine the role of the basic leucine zipper transcription factor ATF-like 3 (Batf3) in the evolution of infection with Leishmania infantum, the causative agent of human visceral leishmaniasis in the Mediterranean Basin and Latin America. For that, Batf3-deficient mice in C57BL/6 background were infected with an L. infantum strain expressing the luciferase gene. Bioluminescent imaging, as well as in vitro parasite titration, demonstrated that Batf3-deficient mice were unable to control hepatic parasitosis as opposed to wild-type C57BL/6 mice. The impaired microbicide capacities of L. infantum-infected macrophages from Batf3-deficient mice mainly correlated with a reduction of parasite-specific IFN-γ production. Our results reinforce the implication of Batf3 in the generation of type 1 immunity against infectious diseases.

Mucosal CD8 T Cell Responses Are Shaped by Batf3-DC After Foodborne Listeria monocytogenes Infection

While immune responses have been rigorously examined after intravenous Listeria monocytogenes (Lm) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with Lm modified to invade murine intestinal epithelium (InlA^MLm). InlA^MLm trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlA^MLm initially disseminated from the gut to the MLN normally in Batf3^–/– mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlA^MLm. At this time Batf3^–/– mice displayed reduced InlA^MLm burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. Batf3^–/– mice also exhibited profound defects in the induction and gut-homing of InlA^MLm-specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in Batf3^–/– mice, indicating a critical role for Batf3 in generating anti-InlA^MLm immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlA^MLm infection and in driving the establishment of intestinal Lm-specific effector T cells.

A Batf3/Nlrp3/IL-18 Axis Promotes Natural Killer Cell IL-10 Production during Listeria monocytogenes Infection

The bacterial pathogen Listeria monocytogenes (Lm) capitalizes on natural killer (NK) cell production of regulatory interleukin (IL)-10 to establish severe systemic infections. Here, we identify regulators of this IL-10 secretion. We show that IL-18 signals to NK cells license their ability to produce IL-10. IL-18 acts independent of IL-12 and STAT4, which co-stimulate IFNγ secretion. Dendritic cell (DC) expression of Nlrp3 is required for IL-18 release in response to the Lm p60 virulence protein. Therefore, mice lacking Nlrp3, Il18, or Il18R fail to accumulate serum IL-10 and are highly resistant to systemic Lm infection. We further show that cells expressing or dependent on Batf3 are required for IL-18-inducing IL-10 production observed in infected mice. These findings explain how Il18 and Batf3 promote susceptibility to bacterial infection and demonstrate the ability of Lm to exploit NLRP3 for the promotion of regulatory NK cell activity.

Activation of p53 in Immature Myeloid Precursor Cells Controls Differentiation into Ly6c+CD103+ Monocytic Antigen-Presenting Cells in Tumors

CD103⁺ dendritic cells are critical for cross-presentation of tumor antigens. Here we have shown that during immunotherapy, large numbers of cells expressing CD103 arose in murine tumors via direct differentiation of Ly6c⁺ monocytic precursors. These Ly6c⁺CD103⁺ cells could derive from bone-marrow monocytic progenitors (cMoPs) or from peripheral cells present within the myeloid-derived suppressor cell (MDSC) population. Differentiation was controlled by inflammation-induced activation of the transcription factor p53, which drove upregulation of Batf3 and acquisition of the Ly6c⁺CD103⁺ phenotype. Mice with a targeted deletion of p53 in myeloid cells selectively lost the Ly6c⁺CD103⁺ population and became unable to respond to multiple forms of immunotherapy and immunogenic chemotherapy. Conversely, increasing p53 expression using a p53-agonist drug caused a sustained increase in Ly6c⁺CD103⁺ cells in tumors during immunotherapy, which markedly enhanced the efficacy and duration of response. Thus, p53-driven differentiation of Ly6c⁺CD103⁺ monocytic cells represents a potent and previously unrecognized target for immunotherapy.

Colonization-induced protection against invasive pneumococcal disease in mice is independent of CD103 driven adaptive immune responses

Nasopharyngeal colonization with Streptococcus pneumoniae (the pneumococcus) is known to mount protective adaptive immune responses in rodents and humans. However, the cellular response of the nasopharyngeal compartment to pneumococcal colonization and its importance for the ensuing adaptive immune response is only partially defined. Here we show that nasopharyngeal colonization with S. pneumoniae triggered substantial expansion of both integrin αE (CD103) positive dendritic cells (DC) and T lymphocytes in nasopharynx, nasal-associated lymphoid tissue (NALT) and cervical lymph nodes (CLN) of WT mice. However, nasopharyngeal de-colonization and pneumococcus-specific antibody responses were similar between WT and CD103 KO mice or Batf3 KO mice. Also, naïve WT mice passively immunized with antiserum from previously colonized WT and CD103 KO mice were similarly protected against invasive pneumococcal disease (IPD). In summary, the data show that CD103 is dispensable for pneumococcal colonization-induced adaptive immune responses in mice.

Absence of Batf3 results in reduced liver pathology in mice infected with Schistosoma japonicum

Background

The involvement of CD8⁺T cells in schistosomiasis is being increasingly appreciated, but the underlying mechanism is not well defined.

Results

In this study, we showed that the absence of Batf3 alleviated liver damage in Batf3^−/− mice infected with S. japonicum. We found alleviated liver granulomatous inflammation in Batf3^−/− mice with schistosomiasis japonica could not be attributed to the difference in schistosome egg or worm burden. The stronger Tc1 cell responses observed in Batf3^−/− mice suggested that the deletion of Batf3 resulted in more activation of CD8⁺T cells unexpectedly during the natural infection of schistosomes. We detected a small amount of CD8α⁺ DCs in the spleen of Batf3^−/− mice at 9w post-infection. This small amount of newly generated CD8α⁺ DCs might contribute to enhanced activation of CD8⁺T cells via cross-presentation and activation which then attenuate hepatic pathological damage found in Batf3^−/− mice.

Conclusions

Our study provides evidence that Batf3 is associated with the immunoregulation of the liver granuloma formation, which may confer a new options for schistosomiasis treatment.

Batf3-dependent CD8α+ Dendritic Cells Aggravates Atherosclerosis via Th1 Cell Induction and Enhanced CCL5 Expression in Plaque Macrophages

Dendritic cells (DCs) play an important role in controlling T cell-mediated adaptive immunity in atherogenesis. However, the role of the basic leucine zipper transcription factor, ATF-like 3 (Batf3)-dependent CD8α⁺ DC subset in atherogenesis remains unclear. Here we show that Batf3^−/− Apoe^−/− mice, lacking CD8α⁺ DCs, exhibited a significant reduction in atherogenesis and T help 1 (Th1) cells compared with Apoe^−/− controls. Then, we found that CD8α⁺ DCs preferentially induce Th1 cells via secreting interleukin-12 (IL-12), and that the expression of interferon-gamma (IFN-γ)or chemokine (C-C motif) ligand 5 (CCL5) in aorta were significantly decreased in Batf3^−/− Apoe^−/− mice. We further demonstrated that macrophages were the major CCL5-expressing cells in the plaque, which was significantly reduced in Batf3^−/− Apoe^−/− mice. Furthermore, we found CCL5 expression in macrophages was promoted by IFN-γ. Finally, we showed that Batf3^−/− Apoe^−/− mice displayed decreased infiltration of leukocytes in the plaque. Thus, CD8α⁺ DCs aggravated atherosclerosis, likely by inducing Th1 cell response, which promoted CCL5 expression in macrophages and increased infiltration of leukocytes and lesion inflammation.

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Ablation of CD8α⁺ DCs in Batf3^−/− Apoe^−/− mice alleviated atherosclerosis, reduced Th1 cells and CCL5 expression.

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Th1 cell cytokine IFN-γ promoted CCL5 expression in macrophages.

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Reduction of Th1 cells and CCL5 expression helps to explain decreased aortic accumulation of inflammatory leukocytes.

Dendritic cells (DCs) play an important role in controlling T cell-mediated adaptive immunity in atherogenesis. However, the role of Batf3-dependent CD8α⁺ DC subset in atherogenesis remains unclear. Here we found that ablation of CD8α⁺ DCs in Batf3^−/− Apoe^−/− mice alleviated atherosclerosis. Our data suggested that Batf3-dependent CD8α⁺ DCs from western diet-treated mice preferentially induce Th1 cell polarization via secreting IL-12. Th1 cells promoted CCL5 expression on macrophages via IFN-γ secretion. Lack of CD8α⁺ DCs-dependent enhancement of Th1 cells and CCL5 expression might explain decreased aortic accumulation of inflammatory leukocytes.

Batf3-dependent CD103(+) dendritic cell accumulation is dispensable for mucosal and systemic antifungal host defense

Dendritic cells (DCs) are critical for defense against a variety of pathogens and the formation of adaptive immune responses. The transcription factor Batf3 is critical for the development of CD103(+)CD11b(-) DCs, which promote IL-12-dependent protective immunity during viral and parasitic infections, dampen Th2 immunity during helminthic infection, and exert detrimental effects during bacterial infection. Whether CD103(+) DCs modulate immunity during systemic or mucosal fungal disease remains unknown. Herein, we report that Batf3 is critical for accumulation of CD103(+) DCs in the kidney and tongue at steady state, for their expansion during systemic and oropharyngeal candidiasis, and for tissue-specific production of IL-12 in kidney but not tongue during systemic and oropharyngeal candidiasis, respectively. Importantly, deficiency of CD103(+) DCs does not impair survival or fungal clearance during systemic or oropharyngeal candidiasis, indicating that Batf3-dependent CD103(+) DC accumulation mediates pathogen- and tissue-specific immune effects.

DNGR-1(+) dendritic cells are located in meningeal membrane and choroid plexus of the noninjured brain

The role and different origin of brain myeloid cells in the brain is central to understanding how the central nervous system (CNS) responds to injury. C-type lectin receptor family 9, member A (DNGR-1/CLEC9A) is a marker of specific DC subsets that share functional similarities, such as CD8α(+) DCs in lymphoid tissues and CD103(+) CD11b(low) DCs in peripheral tissues. Here, we analyzed the presence of DNGR-1 in DCs present in the mouse brain (bDCs). Dngr-1/Clec9a mRNA is expressed mainly in the meningeal membranes and choroid plexus (m/Ch), and its expression is enhanced by fms-like tyrosine kinase 3 ligand (Flt3L), a cytokine involved in DC homeostasis. Using Clec9a(egfp/egfp) mice, we show that Flt3L induces accumulation of DNGR-1-EGFP(+) cells in the brain m/Ch. Most of these cells also express major histocompatibility complex class II (MHCII) molecules. We also observed an increase in specific markers of cDC CD8α+ cells such as Batf-3 and Irf-8, but not of costimulatory molecules such as Cd80 and Cd86, indicating an immature phenotype for these bDCs in the noninjured brain. The presence of DNGR-1 in the brain provides a potential marker for the study of this specific brain cell subset. Knowledge and targeting of brain antigen presenting cells (APCs) has implications for the fight against brain diseases such as neuroinflammation-based neurodegenerative diseases, microbe-induced encephalitis, and brain tumors such as gliomas.

Ontogenic, Phenotypic, and Functional Characterization of XCR1(+) Dendritic Cells Leads to a Consistent Classification of Intestinal Dendritic Cells Based on the Expression of XCR1 and SIRPα

In the past, lack of lineage markers confounded the classification of dendritic cells (DC) in the intestine and impeded a full understanding of their location and function. We have recently shown that the chemokine receptor XCR1 is a lineage marker for cross-presenting DC in the spleen. Now, we provide evidence that intestinal XCR1⁺ DC largely, but not fully, overlap with CD103⁺ CD11b⁻ DC, the hypothesized correlate of “cross-presenting DC” in the intestine, and are selectively dependent in their development on the transcription factor Batf3. XCR1⁺ DC are located in the villi of the lamina propria of the small intestine, the T cell zones of Peyer’s patches, and in the T cell zones and sinuses of the draining mesenteric lymph node. Functionally, we could demonstrate for the first time that XCR1⁺/CD103⁺ CD11b⁻ DC excel in the cross-presentation of orally applied antigen. Together, our data show that XCR1 is a lineage marker for cross-presenting DC also in the intestinal immune system. Further, extensive phenotypic analyses reveal that expression of the integrin SIRPα consistently demarcates the XCR1⁻ DC population. We propose a simplified and consistent classification system for intestinal DC based on the expression of XCR1 and SIRPα.

Dendritic cells in liver injury and fibrosis: shortcomings and promises

The phenotype and function of liver dendritic cells (LDCs) are poorly understood. This Snapshot summarizes our current knowledge on LDCs in the healthy and injured liver, and their role in fibrosis progression and reversal. It also draws attention to various pitfalls in the current experimental design and conclusions based on available data.

Expression of XCR1 Characterizes the Batf3-Dependent Lineage of Dendritic Cells Capable of Antigen Cross-Presentation

Cross-presentation of antigen by dendritic cells (DCs) to CD8⁺ T cells is a fundamentally important mechanism in the defense against pathogens and tumors. Due to the lack of an appropriate lineage marker, cross-presenting DCs in the mouse are provisionally classified as “Batf3-IRF-8-Id2-dependent DCs” or as “CD8⁺ DCs” in the spleen, and as “CD103⁺CD11b⁻ DCs” in the periphery. We have now generated a mAb to XCR1, a chemokine receptor which is specifically expressed on CD8⁺ DCs and a subpopulation of double negative DCs in the spleen. Using this antibody, we have determined that only XCR1⁺CD8⁺ (around 80% of CD8⁺ DCs) and their probable precursors, XCR1⁺CD8⁻ DCs, efficiently take up cellular material and excel in antigen cross-presentation. In lymph nodes (LNs) and peripheral tissues, XCR1⁺ DCs largely, but not fully, correspond to CD103⁺CD11b⁻ DCs. Most importantly, we demonstrate that XCR1⁺ DCs in the spleen, LNs, and peripheral tissues are dependent on the growth factor Flt3 ligand and are selectively absent in Batf3-deficient animals. These results provide evidence that expression of XCR1 throughout the body defines the Batf3-dependent lineage of DCs with a special capacity to cross-present antigen. XCR1 thus emerges as the first surface marker characterizing a DC lineage in the mouse and potentially also in the human.