Inflammasome activation and CCR2-mediated monocyte-derived dendritic cell recruitment restrict Legionella pneumophila infection.

Flagellin-induced NAIP/NLRC4 inflammasome activation and pyroptosis are critical events restricting Legionella pneumophila infection. However, the cellular and molecular dynamics of the in vivo responses against this bacterium are still unclear. We have found temporal coordination of two independent innate immunity pathways in controlling Legionella infection, the inflammasome activation and the CCR2-mediated Mo-DC recruitment. Inflammasome activation was an important player at the early stage of infection by lowering the numbers of bacteria for an efficient bacterial clearance conferred by the Mo-DC at the late stage of the infection. Mo-DC emergence highly depended on CCR2-signaling and dispensed inflammasome activation and pyroptosis. Also, Mo-DC compartment did not rely on the inflammasome machinery to deliver proper immune responses and was the most abundant cytokine-producing among the monocyte-derived cells in the infected lung. Importantly, when the CCR2- and NLRC4-dependent axes of response were simultaneously ablated, we observed an aggravated bacterial burden in the lung of infected mice. Taken together, we showed that inflammasome activation and CCR2-mediated immune response interplay in distinct pathways to restrict pulmonary bacterial infection. These findings extend our understanding of the in vivo integration and cooperation of different innate immunity arms in controlling infectious agents.

MicroRNA-98-5p Inhibits IFI44L-Mediated Differentiation of Dendritic Cells and Activation of Interferon Pathway in Systemic Lupus Erythematosus.

MicroRNA-98-5p (miR-98-5p) plays a protective role in the pathogenesis of autoimmune diseases through anti-inflammatory effects, but little is known about its role in Systemic lupus erythematosus (SLE). Our previous study suggested Interferon-inducible 44 like (IFI44L) overexpressed in monocytes which contributes to the pathogenesis of SLE by enhancing the maturation and functions of monocyte-derived dendritic cells (Mo-DCs), and miR-98-5p can regulate the expression of IFI44L. In this study, we identified miR-98-5p lowly expressed in both peripheral blood mononuclear cells (PBMCs) and monocytes of SLE patients along with high expression of IFI44L. IFI44L serves as target gene of miR-98-5p which inhibits differentiation of Mo-DCs and IFI44L-mediated activation of interferon pathway. We further showed that miR-98-5p promotes methylation of the IFI44L promoter to down-regulate its expression in SLE. Our results reveal an important role for miR-98-5p in the IFI44L-mediated immune imbalance of SLE and suggest a potential therapeutic target for SLE in the future.

Function and autophagy of monocyte-derived dendritic cells is affected by hepatitis B virus infection.

BACKGROUND: The role of dendritic cells and the autophagy state of dendritic cells in the immune response of hepatitis B virus (HBV) infection was still controversial. In this study, we carefully examined the phenotype, function and autophagy pathway of dendritic cells in HBV infection. METHODS: Monocyte-derived dendritic cells from healthy blood donors and patients with chronic HBV infection were stimulated by lipopolysaccharide, supernatant of HepG2.2.15 cells or supernatant of HepG2 cells respectively. Phenotype of dendritic cells was examined by flow cytometry and cytokines secretion was detected by enzyme-linked immunosorbent assay. Autophagy related proteins were detected by western blot and immunofluorescence analysis. RESULTS: Our results showed that the expression of both major histocompatibility complex II molecules and co-stimulated molecules including cluster of differentiation antigen 80, cluster of differentiation antigen 86 in the monocyte-derived dendritic cells from patients with chronic HBV infection was significantly higher than that from healthy donors when cultured with supernatant of HepG2.2.15 cells. The amount of cytokines, including tumour necrosis factor-α, interleukin-10 and interleukin-12, secreted by monocyte-derived dendritic cells from patients with chronic HBV infection was also significantly higher than that from healthy donors when stimulate by HBV. Interestingly, the expression level of autophagy-related proteins including autophagy-related protein5 and associated protein 1 light chain in dendritic cells from patients with chronic HBV infection was significantly increased when compared with that from healthy donors when re-exposed to HBV. CONCLUSIONS: Our results indicated that dendritic cells from patients with chronic HBV infection could intensively present antigen and express co-stimulatory molecules. The increased activation of dendritic cells might be related to the enhanced autophagy of dendritic cells in HBV infection.

A Morbillivirus Infection Shifts DC Maturation Toward a Tolerogenic Phenotype to Suppress T Cell Activation.

Viruses have evolved numerous strategies to impair immunity so that they can replicate more efficiently. Among those, the immunosuppressive effects of morbillivirus infection can be particularly problematic, as they allow secondary infections to take hold in the host, worsening disease prognosis. In the present work, we hypothesized that the highly contagious morbillivirus peste des petits ruminants virus (PPRV) could target monocytes and dendritic cells (DC) to contribute to the immunosuppressive effects produced by the infection. Monocytes isolated from healthy sheep, a natural host of the disease, were able be infected by PPRV and this impaired the differentiation and phagocytic ability of immature monocyte-derived DC (MoDC). We also assessed PPRV capacity to infect differentiated MoDC. Ovine MoDC could be productively infected by PPRV, and this drastically reduced MoDC capacity to activate allogeneic T cell responses. Transcriptomic analysis of infected MoDC indicated that several tolerogenic DC signature genes were upregulated upon PPRV infection. Furthermore, PPRV-infected MoDC could impair the proliferative response of autologous CD4+ and CD8+ T cell to the mitogen concanavalin A (ConA), which indicated that DC targeting by the virus could promote immunosuppression. These results shed new light on the mechanisms employed by morbillivirus to suppress the host immune responses. IMPORTANCE Morbilliviruses pose a threat to global health given their high infectivity. The morbillivirus peste des petits ruminants virus (PPRV) severely affects small-ruminant-productivity and leads to important economic losses in communities that rely on these animals for subsistence. PPRV produces in the infected host a period of severe immunosuppression that opportunistic pathogens exploit, which worsens the course of the infection. The mechanisms of PPRV immunosuppression are not fully understood. In the present work, we demonstrate that PPRV can infect professional antigen-presenting cells called dendritic cells (DC) and disrupt their capacity to elicit an immune response. PPRV infection promoted a DC activation profile that favored the induction of tolerance instead of the activation of an antiviral immune response. These results shed new light on the mechanisms employed by morbilliviruses to suppress the immune responses.

1,25(OH)2D3 Differently Modulates the Secretory Activity of IFN-DC and IL4-DC: A Study in Cells from Healthy Donors and MS Patients.

Immune mechanisms play an essential role in driving multiple sclerosis (MS) and altered trafficking and/or activation of dendritic cells (DC) were observed in the central nervous system and cerebrospinal fluid of MS patients. Interferon ß (IFNß) has been used as a first-line therapy in MS for almost three decades and vitamin D deficiency is a recognized environmental risk factor for MS. Both IFNß and vitamin D modulate DC functions. Here, we studied the response to 1,25-dihydoxyvitamin D3 (1,25(OH)2D3) of DC obtained with IFNß/GM-CSF (IFN-DC) compared to classically derived IL4-DC, in three donor groups: MS patients free of therapy, MS patients undergoing IFNß therapy, and healthy donors. Except for a decreased CCL2 secretion by IL4-DC from the MS group, no major defects were observed in the 1,25(OH)2D3 response of either IFN-DC or IL4-DC from MS donors compared to healthy donors. However, the two cell models strongly differed for vitamin D receptor level of expression as well as for basal and 1,25(OH)2D3-induced cytokine/chemokine secretion. 1,25(OH)2D3 up-modulated IL6, its soluble receptor sIL6R, and CCL5 in IL4-DC, and down-modulated IL10 in IFN-DC. IFN-DC, but not IL4-DC, constitutively secreted high levels of IL8 and of matrix-metalloproteinase-9, both down-modulated by 1,25(OH)2D3. DC may contribute to MS pathogenesis, but also provide an avenue for therapeutic intervention. 1,25(OH)2D3-induced tolerogenic DC are in clinical trial for MS. We show that the protocol of in vitro DC differentiation qualitatively and quantitatively affects secretion of cytokines and chemokines deeply involved in MS pathogenesis.

Bone morphogenetic protein signaling regulates skin inflammation via modulating dendritic cell function.

BACKGROUND: Bone morphogenetic proteins (BMPs) are members of the TGF-ß family that signal via the BMP receptor (BMPR) signaling cascade, distinct from canonical TGF-ß signaling. BMP downstream signaling is strongly induced within epidermal keratinocytes in cutaneous psoriatic lesions, and BMP7 instructs monocytic cells to acquire characteristics of psoriasis-associated Langerhans dendritic cells (DCs). Regulatory T (Treg)-cell numbers strongly increase during psoriatic skin inflammation and were recently shown to limit psoriatic skin inflammation. However, the factors mediating Treg-cell accumulation in psoriatic skin currently remain unknown. OBJECTIVE: We sought to investigate the role of BMP signaling in Treg-cell accumulation in psoriasis. METHODS: The following methods were used: immunohistology of patients and healthy controls; ex vivo models of Treg-cell generation in the presence or absence of Langerhans cells; analysis of BMP versus canonical TGF-ß signaling in DCs and Treg cells; and modeling of psoriatic skin inflammation in mice lacking the BMPR type 1a in CD11c+ cells. RESULTS: We here demonstrated a positive correlation between Treg-cell numbers and epidermal BMP7 expression in cutaneous psoriatic lesions and show that unlike Treg cells from healthy skin, a portion of inflammation-associated Treg cells exhibit constitutive-active BMP signaling. We further found that BMPR signaling licenses inflammation-associated Langerhans cell/DC to gain an enhanced capacity to promote Treg cells via BMPR-mediated CD25 induction and that this effect is associated with reduced skin inflammation. CONCLUSIONS: Psoriatic lesions are marked by constitutive high BMP7/BMPR signaling in keratinocytes, which instructs inflammatory DCs to gain enhanced Treg-cell-stimulatory activity. Locally secreted BMP7 can directly promote Treg-cell generation through the BMP signaling cascade.

In vitro activation and maturation of human mononuclear phagocytes by stimulation with liposomes coated with a neoglycolipid containing α1-3, α1-6-mannotriose.

In this study, we assessed the potential of liposomes coated with a neoglycolipid containing α1-3,α1-6-mannotriose residues (Man3-DPPE; Manα1-6(Manα1-3)Manitol-DPPE) for in vitro activation and maturation of human mononuclear phagocytes. In response to treatment with Man3-DPPE-coated liposomes (Man3-OMLs), PMA-stimulated human THP-1 cells showed enhanced expression of CD40, CD80 and HLA-DR and secreted significant levels of IL-12p40. Among various linkages of Man2-DPPE-coated liposomes, only liposomes coated with Manα1-6Manitol-DPPE (α1-6Man2-DPPE) induced these cellular responses similarly to Man3-OML treatment. Liposomes coated with Manα1-6(Manα1-3)Manα1-6(Manα1-3)Manitol-DPPE (Man5-DPPE) failed to activate the cells. These results suggest that an unsubstituted α1-6Man branch bound to a mannitol unit at the reducing end in Man3-DPPE is required for in vitro activation of human mononuclear phagocytes. Man3-OML-induced IL-12p40 production was not inhibited by BAY11-7082, an inhibitor of the MyD88-dependent signaling network, suggesting that TLRs are not involved in activation of human mononuclear phagocytes by Man3-OMLs. Stimulation of inflammatory monocytes or monocyte-derived dendritic cells (moDCs) with Man3-OMLs also induced enhanced expression of co-stimulatory molecules, HLA-DR, and CCR7, and IL-12p40 production from both types of cells. In response to Man3-OML treatment, moDCs but not inflammatory monocytes produced bioactive IL-12p70, which was enhanced by CD40 ligation. Thus, Man3-OMLs can activate naïve human mononuclear phagocytes and lead human moDCs to a fully matured status in vitro to elicit CTLs and a Th1 response without addition of inflammatory cytokines or TLR agonists.

Immunobiology of Atherosclerosis: A Complex Net of Interactions.

Cardiovascular disease is the leading cause of mortality worldwide, and atherosclerosis the principal factor underlying cardiovascular events. Atherosclerosis is a chronic inflammatory disease characterized by endothelial dysfunction, intimal lipid deposition, smooth muscle cell proliferation, cell apoptosis and necrosis, and local and systemic inflammation, involving key contributions to from innate and adaptive immunity. The balance between proatherogenic inflammatory and atheroprotective anti-inflammatory responses is modulated by a complex network of interactions among vascular components and immune cells, including monocytes, macrophages, dendritic cells, and T, B, and foam cells; these interactions modulate the further progression and stability of the atherosclerotic lesion. In this review, we take a global perspective on existing knowledge about the pathogenesis of immune responses in the atherosclerotic microenvironment and the interplay between the major innate and adaptive immune factors in atherosclerosis. Studies such as this are the basis for the development of new therapies against atherosclerosis.

Interleukin 35: Inhibitory regulator in monocyte-derived dendritic cell maturation and activation.

IL-35, a novel IL-12 family member, is a potent inhibitory cytokine predominantly produced by regulatory T and B lymphocytes that exerts optimal suppression in immune response. However, it remains unclear whether IL-35 plays an inhibitory role on human dendritic cells. In the present study, we focused on the possible immunosuppressive effect of IL-35 on the differentiation, maturation and function of monocyte-derived DCs (MoDCs). Addition of exogenous IL-35 was able to partially suppress MoDCs differentiation in vitro. Subsequently, LPS was used for the maturation of MoDCs and IL-35 was found to mainly restrain the maturation of MoDCs, characterized by the remarkable down-regulation of costimulatory molecules, CD83 and HLA-DR as well as a reduced production of pro-inflammatory cytokines (IL-12p70, IFN-γ, and TNF-α). Furthermore, IL-35-treated MoDCs exhibited strong inhibition in the proliferation of allogeneic CD4+/CD8+ T lymphocytes. Meanwhile, IL-35-treated MoDCs also suppressed the polarization of naïve CD4+ T lymphocytes towards Th1 phenotype and impaired CD8+ T cells allogeneic responses. And the foregoing suppression of MoDCs maturation and function by IL-35 might be due to the aberrant activation of STAT1/STAT3 and inhibition of p38 MAPK/NF-κB signaling pathway. Our results demonstrated for the first time that IL-35 played a critical role in modulating not only adaptive immune response, but also innate immune response. The inhibitory effect of IL-35 on MoDCs maturation and function may facilitate the development of promising therapeutic interventions in tumors and other diseases.

Differential capacity of human interleukin-4 and interferon-α monocyte-derived dendritic cells for cross-presentation of free versus cell-associated antigen.

Dendritic cells (DC) vaccination is a potent therapeutic approach for inducing tumor-directed immunity, but challenges remain. One of the particular interest is the induction of an immune response targeting multiple (unknown) tumor-associated antigens (TAA), which requires a polyvalent source of TAA. Previously, we described the preferred use of apoptotic cell-derived blebs over the larger apoptotic cell remnants, as a source of TAA for both in situ loading of skin-resident DC and in vitro loading of monocyte-derived DC (MoDC). Recent reports suggest that MoDC cultured in the presence of GM-CSF supplemented with IFNα (IFNα MoDC), as compared to IL-4 (IL-4 MoDC), have an increased capacity to cross-present antigen to CD8(+) T cells. As culture conditions, maturation methods and antigen sources differ between the conducted studies, we analyzed the functional differences between IL-4 MoDC and IFNα MoDC, loaded with blebs, in a head-to-head comparison using commonly used protocols. Our data show that both MoDC types are potent (cross-) primers of CD8(+) T cells. Whereas IFNα MoDC were more potent in their capacity to cross-present a 25-mer MART-1 synthetic long peptide (SLP) to a MART-1aa26-35 recognizing CD8(+) T cell line, IL-4 MoDC proved more potent cross-primers of antigen-specific CD8(+) T cells when loaded with blebs. The latter is likely due to the observed greater capacity of IL-4 MoDC to ingest apoptotic blebs. In conclusion, our data indicate the use of IFNα MoDC over IL-4 MoDC in the context of DC vaccination with SLP, whereas IL-4 MoDC are preferred for vaccination with bleb-derived antigens.

Monocyte-derived dendritic cells can be detected in urine of kidney transplant recipients with pathogenic asymptomatic bacteriuria.

Urinary tract infections (UTI) are an important clinical problem in kidney transplant recipients (KTR). Asymptomatic bacteriuria (ASB) is frequent in these patients and often resolved by the immune system, but a significant proportion may progress to complicated UTI, which may compromise allograft function and survival. It is essential to determine the involvement of the immune system in the infectious process. Dendritic cells (DCs) are recognised as playing a pivotal role in initiating inflammatory responses capable of priming antigen-specific T cells, a crucial step in determining the fate of local inflammation. Little is known about their role in the control of UTI. In this brief communication, we report an incidental finding in a group of 16 stable KTR in which monocyte-derived dendritic cells (ModDCs), analysed by flow cytometry, were found in urine of patients with ASB and high bacterial counts >107 cfu/ml. Within this group, one patient developed pyelonephritis in the following days. These findings suggest that the immune system, in particular DCs, may be recruited during the course of a UTI and, to our knowledge, present for the first time evidence that inflammatory ModDCs can be detected in urine. Their frequency may reflect the degree of infection. This finding suggests the potential for exploring whether these cells may be useful in distinguishing between pathogenic ASB and those that can be resolved by the immune system.

The post-viral GPNMB+ immune niche persists in long-term Covid, asthma, and COPD.

Epithelial injury calls for a regenerative response from a coordinated network of epithelial stem cells and immune cells. Defining this network is key to preserving the repair process for acute resolution, but also for preventing a remodeling process with chronic dysfunction. We recently identified an immune niche for basal-epithelial stem cells using mouse models of injury after respiratory viral infection. Niche function depended on an early sentinel population of monocyte-derived dendritic cells (moDCs) that provided ligand GPNMB to basal-ESC receptor CD44 for reprogramming towards chronic lung disease. These same cell and molecular control points worked directly in mouse and human basal-ESC organoids, but the findings were not yet validated in vivo in human disease. Further, persistence of GPNMB expression in moDCs and M2-macrophages in mouse models suggested utility as a long-term disease biomarker in humans. Here we show increased expression of GPNMB localized to moDC-macrophage populations in lung tissue samples from long-term Covid, asthma, and COPD. The findings thereby provide initial evidence of a persistent and correctable pathway from acute injury to chronic disease with implications for cellular reprogramming and inflammatory memory.

Comparative analysis of monocyte-derived dendritic cell phenotype and T cell stimulatory function in patients with acute-on-chronic liver failure with different clinical parameters.

Background: Acute-on-Chronic Liver Failure (ACLF) patients experience systemic inflammation as well as immune dysfunction and exhaustion. The phenotype and functionality of monocyte-derived dendritic cells in ACLF patients with different clinical parameters have not been elucidated. Methods: This study included 37 cases of ACLF, 20 cases of Chronic Hepatitis B (CHB) patients, and 12 healthy controls. Demographic and laboratory parameters were collected from the enrolled patients. Peripheral blood samples were obtained from the participants. Monocyte-derived dendritic cells were induced and cultured, followed by co-culturing with T cells from the patients. Cell surface markers and intracellular markers were analyzed using flow cytometry. The relationship between these markers and clinical parameters was compared. Results: Our study found that ACLF patients had lower expression levels of HLA-DR, CD86, and CD54 on monocyte-derived dendritic cells compared to both CHB patients and healthy controls. IL-4, GM-CSF, and alcohol were found to promote the expression of HLA-DR, CD86, and CD54 on monocyte-derived dendritic cells. In ACLF patients, higher levels of procalcitonin (PCT), lower levels of albumin, decreased prothrombin activity and deceased patients were associated with lower expression of HLA-DR, CD86, and CD54 on monocyte-derived dendritic cells. Peripheral blood mononuclear cells (PBMCs), after removing adherent cells, were co-cultured with monocyte-derived DC. Our study revealed that patients with infection and low albumin levels exhibited a decreased proportion of T cell subsets within PBMCs. Additionally, these patients' T cells showed lower levels of Ki-67 and interferon-gamma (IFN-γ) production. Conclusion: ACLF patients exhibit varying clinical states, with differences in the phenotype and the ability of monocyte-derived dendritic cells to stimulate T cells. Alcohol can stimulate the maturation of monocyte-derived dendritic cells.

Preliminary Study of the Relationship between Osteopontin and Relapsed Hodgkin's Lymphoma.

The primary objective of this study was to investigate the potential role of tissue osteopontin, also known as secreted phosphoprotein 1 (SPP1), as a contributing factor to an unfavorable prognosis in classical Hodgkin's lymphoma (HL) patients who received the same treatment protocol. The study involved 44 patients aged 4-22 years, with a median follow-up period of 3 years. Patients with higher levels of SPP1 were associated with tissue necrosis and inflammation, and there was a trend toward a poorer prognosis in this group. Before therapy, we found a correlation between positron emission tomography (PET) scans and logarithmic SPP1 levels (p = 0.035). However, the addition of SPP1 levels did not significantly enhance the predictive capacity of PET scans for recurrence or progression. Elevated SPP levels were associated with tissue mRNA counts of chemotactic and inflammatory chemokines, as well as specific monocyte/dendritic cell subtypes, defined by IL-17RB, PLAUR, CXCL8, CD1A, CCL13, TREM1, and CCL24 markers. These findings contribute to a better understanding of the potential factors influencing the prognosis of HL patients and the potential role of SPP1 in the disease. While the predictive accuracy of PET scans did not substantially improve during the study, the results underscore the complexity of HL and highlight the relationships between SPP1 and other factors in the context of HL relapse.

An inter-laboratory comparison of an NLRP3 inflammasome activation assay and dendritic cell maturation assay using a nanostructured lipid carrier and a polymeric nanomedicine, as exemplars.

Nanoparticles including nanomedicines are known to be recognised by and interact with the immune system. As these interactions may result in adverse effects, for safety evaluation, the presence of such interactions needs to be investigated. Nanomedicines in particular should not unintendedly interact with the immune system, since patient's exposure is not minimised as in the case of 'environmental' nanoparticles, and repeated exposure may be required. NLRP3 inflammasome activation and dendritic cell (DC) maturation are two types of immune mechanisms known to be affected by nanoparticles including nanomedicines. NLRP3 inflammasome activation results in production of the pro-inflammatory cytokines IL-1ß and IL-18, as well as a specific type of cell death, pyroptosis. Moreover, chronic NLRP3 inflammasome activation has been related to several chronic diseases. Upon maturation, DC activate primary T cells; interference with this process may result in inappropriate activation and skewing of the adaptive immune response. Here, we evaluated the effect of two nanomedicines, representing nanostructured lipid carriers and polymers, on these two assays. Moreover, with a view to possible future standardisation and regulatory application, these assays were subject to an inter-laboratory comparison study using common SOPs. One laboratory performed three independent NLRP3 inflammasome activation experiments, while the other performed a single experiment. Two laboratories each performed three independent DC maturation experiments. While the nanostructured lipid carrier only showed marginal effects, the polymers showed major cytotoxicity. No evidence for inflammasome activation or DC maturation was demonstrated. Intra- and inter-laboratory comparison showed clearly reproducible results.

Evaluation of ß-Catenin Inhibition of Axitinib and Nitazoxanide in Human Monocyte-Derived Dendritic Cells.

Modulation of ß-catenin signaling has attractive therapeutic potential in cancer immunotherapy. Several studies have found that ß-catenin can mediate immune evasion in cancer and promote anti-inflammatory features of antigen-presenting dendritic cells. Many small molecular compounds that inhibit Wnt/ß-catenin signaling are currently in clinical development, but none have entered routine clinical use. New inhibitors of ß-catenin signaling are consequently desirable. Here, we have tested, in monocyte-derived dendritic cells, the effects of two small molecular compounds, axitinib and nitazoxanide, that previously have been discovered to inhibit ß-catenin signaling in colon cancer cells. Immature and lipopolysaccharide-matured dendritic cells prepared from healthy blood donor buffy coats were stimulated with 6-bromoindirubin-3'-oxime (6-BIO) to boost basal ß-catenin activity, and the effects of axitinib and nitazoxanide were compared with the commercial ß-catenin inhibitor ICG-001. Assays, including genome-wide RNA-sequencing, indicated that neither axitinib nor nitazoxanide demonstrated considerable ß-catenin inhibition. Both compounds were found to be less toxic to monocyte-derived dendritic cells than either 6-BIO or ICG-001. Axitinib stimulated several aspects of dendritic cell function, such as IL12-p70 secretion, and counteracted IL-10 secretion, according to the present study. However, neither axitinib nor nitazoxanide were found to be efficient ß-catenin inhibitors in monocyte-derived dendritic cells.

Antigen presentation by mouse monocyte-derived cells: Re-evaluating the concept of monocyte-derived dendritic cells.

Antigen presentation is a key feature of classical dendritic cells (cDCs). Numerous studies have also reported in mouse that, upon inflammation, monocytes enter tissues and differentiate into monocyte-derived DCs (mo-DC) that have the ability to present antigens to T cells. However, a population of inflammatory cDCs sharing phenotypic features with mo-DC has been recently described, challenging the existence of in vivo-generated mo-DC. Here we review studies describing mouse mo-DC in the light of these findings, and evaluate the in vivo evidence for monocyte-derived antigen-presenting cells. We examine the strategies used to demonstrate the monocytic origin of these cells. Finally, we propose that mo-DC play a complementary role to cDCs, by presenting antigens to effector T cells locally in tissues.

Japanese Encephalitis Virus Infected Human Monocyte-Derived Dendritic Cells Activate a Transcriptional Network Leading to an Antiviral Inflammatory Response.

A comprehensive understanding of the human immune response to virus infection is imperative for developing effective therapies, antivirals, and vaccines. Dendritic cells (DCs) are among the first cells to encounter the virus and are also key antigen-presenting cells that link the innate and adaptive immune system. In this study, we focus on the human immune response to the mosquito-borne Japanese encephalitis virus (JEV), which is the leading cause of virus-induced encephalitis in south-east Asia and has the potential to become a global pathogen. We describe the gene regulatory circuit of JEV infection in human monocyte-derived DCs (moDCs) along with its functional validation. We observe that JEV can productively infect human moDCs leading to robust transcriptional activation of the interferon and NF-κB-mediated antiviral and inflammatory pathways. This is accompanied with DC maturation and release of pro-inflammatory cytokines and chemokines TNFα, IL-6, IL-8, IL-12, MCP-1. and RANTES. JEV-infected moDCs activated T-regulatory cells (Tregs) in allogenic mixed lymphocyte reactions (MLR) as seen by upregulated FOXP3 mRNA expression, suggestive of a host response to reduce virus-induced immunopathology. The virus also downregulated transcripts involved in Peroxisome Proliferator Activated Receptor (PPAR) signalling and fatty acid metabolism pathways suggesting that changes in cellular metabolism play a crucial role in driving the DC maturation and antiviral responses. Collectively, our data describe and corroborate the human DC transcriptional network that is engaged upon JEV sensing.

Granulocyte Macrophage-Colony Stimulating Factor Produces a Splenic Subset of Monocyte-Derived Dendritic Cells That Efficiently Polarize T Helper Type 2 Cells in Response to Blood-Borne Antigen.

Dendritic cells (DCs) are key antigen-presenting cells that prime naive T cells and initiate adaptive immunity. Although the genetic deficiency and transgenic overexpression of granulocyte macrophage-colony stimulating factor (GM-CSF) signaling were reported to influence the homeostasis of DCs, the in vivo development of DC subsets following injection of GM-CSF has not been analyzed in detail. Among the treatment of mice with different hematopoietic cytokines, only GM-CSF generates a distinct subset of XCR1-33D1- DCs which make up the majority of DCs in the spleen after three daily injections. These GM-CSF-induced DCs (GMiDCs) are distinguished from classical DCs (cDCs) in the spleen by their expression of CD115 and CD301b and by their superior ability to present blood-borne antigen and thus to stimulate CD4+ T cells. Unlike cDCs in the spleen, GMiDCs are exceptionally effective to polarize and expand T helper type 2 (Th2) cells and able to induce allergic sensitization in response to blood-borne antigen. Single-cell RNA sequencing analysis and adoptive cell transfer assay reveal the sequential differentiation of classical monocytes into pre-GMiDCs and GMiDCs. Interestingly, mixed bone marrow chimeric mice of Csf2rb+/+ and Csf2rb-/- demonstrate that the generation of GMiDCs necessitates the cis expression of GM-CSF receptor. Besides the spleen, GMiDCs are generated in the CCR7-independent resident DCs of the LNs and in some peripheral tissues with GM-CSF treatment. Also, small but significant numbers of GMiDCs are generated in the spleen and other tissues during chronic allergic inflammation. Collectively, our present study identifies a splenic subset of CD115hiCD301b+ GMiDCs that possess a strong capacity to promote Th2 polarization and allergic sensitization against blood-borne antigen.

Evaluation of the Immune Response of a Candidate Phage-Based Vaccine against Rhipicephalus microplus (Cattle Tick).

Cattle tick (Rhipicephalus microplus) represents a severe problem causing substantial economic losses, estimated in billions of dollars annually. Currently, chemical acaricides represent the most widely used control method. However, several problems such as resistance have been described. Phage-based vaccines represent a fast and low-cost tool for antigen delivery. In this regard, the objective of the present work was to develop a candidate phage-based vaccine displaying a cattle tick antigen (Bm86-derived Sbm7462 antigen) on the surface of bacteriophage M13. Phage ELISA and dot blotting analysis confirmed the display of the antigen. Vaccine immunogenicity was evaluated using a bovine monocyte-derived dendritic cell-based ex vivo assay and a murine in vivo assay. The ex vivo model showed the maturation of dendritic cells after being pulsed with the phage-based vaccine. The humoral response was confirmed in the in vivo assay. These results demonstrated the capacity of the phage-based vaccine to induce both humoral and cellular immune-specific responses. Importantly, this is the first report describing a control method for cattle ticks using a candidate phage-based vaccine. Further studies to evaluate the immunogenicity in a bovine model are needed. The current approach represents a promising alternative to control cattle tick infestations.