Refine
Has Fulltext
- yes (27)
Is part of the Bibliography
- yes (27)
Year of publication
Document Type
- Journal article (20)
- Doctoral Thesis (7)
Language
- English (27) (remove)
Keywords
- dendritic cells (27) (remove)
Institute
- Institut für Virologie und Immunbiologie (7)
- Medizinische Klinik und Poliklinik II (6)
- Graduate School of Life Sciences (5)
- Theodor-Boveri-Institut für Biowissenschaften (4)
- Institut für Hygiene und Mikrobiologie (2)
- Institut für Molekulare Infektionsbiologie (2)
- Institut für Pharmazie und Lebensmittelchemie (2)
- Klinik und Poliklinik für Allgemein-, Viszeral-, Gefäß- und Kinderchirurgie (Chirurgische Klinik I) (2)
- Rudolf-Virchow-Zentrum (2)
- Abteilung für Molekulare Innere Medizin (in der Medizinischen Klinik und Poliklinik II) (1)
Dendritic cells (DCs) are major players in the control of adaptive tolerance and immunity. Therefore, their specific generation and adoptive transfer into patients or their in vivo targeting is attractive for clinical applications. While injections of mature immunogenic DCs are tested in clinical trials, tolerogenic DCs still are awaiting this step. Besides the tolerogenic potential of immature DCs, also semi-mature DCs can show tolerogenic activity but both types also bear unfavorable features. Optimal tolerogenic DCs, their molecular tool bar, and their use for specific diseases still have to be defined. Here, the usefulness of in vitro generated and adoptively transferred semi-mature DCs for tolerance induction is outlined. The in vivo targeting of semi-mature DCs as represented by steady state migratory DCs are discussed for treatment of autoimmune diseases and allergies. First clinical trials with transcutaneous allergen application may point to their therapeutic use in the future.
The role of host dendritic cells during the effector phase of intestinal graft-versus-host disease
(2014)
Monocytes can be functionally divided in two subsets, both capable to differentiate into dendritic cells (DCs): CX3CR1loCCR2+ classical monocytes, actively recruited to the sites of inflammation and direct precursors of inflammatory DCs; and CX3CR1hiCCR2− non-classical monocytes, characterized by CX3CR1-dependent recruitment to non-inflamed tissues. Yet, the function of non-classical monocyte-derived DCs (nc-mo-DCs), and the factors, which trigger their recruitment and DC differentiation, have not been clearly defined to date. Here we show that in situ differentiated nc-moDCs mediate immunosuppression in the context of intestinal graft-versus-host disease (GVHD).
Employing multi-color confocal microscopy we observed a dramatic loss of steady state host-type CD103+ DC subset immediately after transplantation, followed by an enrichment of immune-regulatory CD11b+ nc-moDCs. Parabiosis experiments revealed that tissue-resident non-classical CX3CR1+ monocytes differentiated in situ into intestinal CD11b+ nc-moDCs after allogeneic hematopoietic cell transplantation (allo-HCT). Differentiation of this intestinal DC subset depended on CSF-1 but not on Flt3L, thus defining the precursors as monocytes and not pre-DCs. Importantly, CX3CR1 but not CCR2 was required for this DC subset differentiation, hence defining the precursors as non-classical monocytes. In addition, we identify PD-L1 expression by CX3CR1+ nc-moDCs as the major mechanism they employ to suppress alloreactive T cells during acute intestinal GVHD. All together, we demonstrate that host nc-moDCs surprisingly mediate immunosuppression in the context of murine intestinal GVHD – as opposed to classical “inflammatory” monocyte-derived dendritic cells (mo-DCs) – via coinhibitory signaling. This thorough study unravels for the first time a biological function of a - so far only in vitro and phenotypically described - DC subset. Our identification of this beneficial immunoregulatory DC subset points towards alternate future strategies in underpinning molecular pathways to foster their function. We describe an unexpected mechanism of nc-moDCs in allo-HCT and intestinal GVHD, which might also be important for autoimmune disorders or infections of the gastrointestinal tract.
Background: Stimulation of CD40 can augment anti-cancer T cell immune responses by triggering effective activation and maturation of antigen-presenting cells (APCs). Although CD40 agonists have clinical activity in humans, the associated systemic activation of the immune system triggers dose-limiting side-effects.
Methods: To increase the tumor selectivity of CD40 agonist-based therapies, we developed an approach in which soluble trimeric CD40L (sCD40L) is genetically fused to tumor targeting antibody fragments, yielding scFv: CD40L fusion proteins. We hypothesized that scFv: CD40L fusion proteins would have reduced CD40 agonist activity similar to sCD40L but will be converted to a highly agonistic membrane CD40L-like form of CD40L upon anchoring to cell surface exposed antigen via the scFv domain.
Results: Targeted delivery of CD40L to the carcinoma marker EpCAM on carcinoma cells induced dose-dependent paracrine maturation of DCs similar to 20-fold more effective than a non-targeted control scFv: CD40L fusion protein. Similarly, targeted delivery of CD40L to the B cell leukemia marker CD20 induced effective paracrine maturation of DCs. Of note, the CD20-selective delivery of CD40L also triggered loss of cell viability in certain B cell leukemic cell lines as a result of CD20-induced apoptosis.
Conclusions: Targeted delivery of CD40L to cancer cells is a promising strategy that may help to trigger cancer-localized activation of CD40 and can be modified to exert additional anti-cancer activity via the targeting domain.
Abstract
Background
HLA-G is a non-classical MHC class I molecule which exerts strong immunosuppressive effects on various immune cells. Several membrane-bound and soluble isoforms are known. Physiologically, HLA-G is predominantly expressed in the placenta, where it contributes to protecting the semi-allogeneic embryo from rejection by the maternal immune system. However, HLA-G is also often upregulated during tumourigenesis, such as in ovarian cancer. The aim of this thesis is to investigate how soluble HLA-G may contribute to local immunosuppression in ovarian carcinomas, and to characterize HLA-G expression in different ovarian carcinoma subtypes and metastases.
Results
As reported by others, physiological HLA-G expression is restricted to few tissues, such as placenta and testes. Here, HLA-G was also detected in the medulla of the adrenal gland. In contrast, HLA-G expression was frequently detected in tumours of all assessed subtypes of ovarian carcinomas (serous, mucinous, endometrioid and clear cell). Highest expression levels were detected in high-grade serous carcinomas. In primary tumours, expression of HLA-G correlated with expression of classical MHC class I molecules HLA-A, -B and -C. Surprisingly, high levels of HLA-G were also detected on dendritic cells in local lymph nodes. As no expression of HLA-G was inducible in monocytes or dendritic cells from healthy donors in response to IL-10 or IL-4, we speculated that tumour-derived soluble HLA-G might be transferred to dendritic cells via the lymphatic system. Accordingly, high levels of tumour-derived soluble HLA-G were detected in ovarian cancer ascites samples. In vitro, dendritic cells expanded in the presence of IL-4, IL-10 and GM-CSF (DC-10) were particularly prone to binding high amounts of soluble HLA-G via ILT receptors. Furthermore, HLA-G loaded DC-10 cells inhibited the proliferation of CD8 effector cells and induced regulatory T cells, even when the DC-10 cells had been fixed with paraformaldehyde.
Conclusion
The immunosuppressive molecule HLA-G is overexpressed in high-grade serous ovarian carcinomas, which account for the majority of ovarian cancers. In particular tumours with a high mutational burden and intact expression of classical, immunogenic MHC class Ia molecules may use HLA-G to escape from immunosurveillance. Additionally, tumour-derived soluble HLA-G may inhibit adaptive immune responses by binding to dendritic cells in local lymph nodes. Dendritic cells usually play a decisive role in the initiation of adaptive anti-tumour immune responses by presenting tumour antigens to cytotoxic T cells. In contrast, dendritic cells loaded with soluble HLA-G inhibit the proliferation of effector T cells and promote the induction of regulatory T cells. Thus, soluble HLA-G that is transferred to dendritic cells via lymphatic vessels may enable ovarian carcinomas to remotely suppress anti-tumour immune responses in local lymph nodes. This novel immune-escape mechanism may also exist in other solid tumours that express HLA-G.
Cutaneous leishmaniasis is endemic in tropical and subtropical regions of the world. Effective vaccination strategies are urgently needed because of the emergence of drug-resistant parasites and severe side effects of chemotherapy. The research group of Heidrun Moll previously established a DC-based vaccination strategy to induce complete and long-lasting immunity to experimental leishmaniasis using LmAg-loaded and CpG ODN-activated DC as a vaccine carrier. Prevention of tissue damages at the site of L. major inoculation can be achieved if the BALB/c mice were systemically given LmAg-loaded BMDC that had been exposed to CpG ODN. The interest in further exploring the role of IL-4 aroused as previous studies allowed establishing that IL-4 was involved in the redirection of the immune response towards a type 1 profile. Thus, wt BALB/c mice or DC-specific CD11ccreIL-4Rα-/lox BALB/c mice were given either wt or IL-4Rα-deficient LmAg-loaded BMDC exposed or not to CpG ODN prior to inoculation of 2 x 105 stationary phase L. major promastigotes into the BALB/c footpad. The results provide evidence that IL4/IL-4Rα-mediated signaling in the vaccinating DC is required to prevent tissue damages at the site of L. major inoculation, as properly conditioned wt DC but not IL-4Rα-deficient DC were able to confer resistance. Furthermore, uncontrolled L. major population size expansion was observed in the footpad and the footpad draining LN in CD11ccreIL-4Rα-/lox mice immunized with CpG ODN-exposed LmAg-loaded IL-4Rα-deficient DC, indicating the influence of IL-4R-mediated signaling in host DC to control parasite replication. In addition, no footpad damage was observed in BALB/c mice that were systemically immunized with LmAg-loaded wt DC doubly exposed to CpG ODN and recombinant IL-4. Discussing these findings allow the assumption that triggering the IL4/IL4Rα signaling pathway could be a precondition when designing vaccines aimed to prevent damaging processes in tissues hosting intracellular microorganisms.
The human intestinal parasite Schistosoma mansoni causes a chronic disease, schistosomiasis or bilharzia. According to the current literature, the parasite induces vigorous immune responses that are controlled by Th2 helper cells at the expense of Th1 helper cells. The latter cell type is, however, indispensable for anti-viral immune responses. Remarkably, there is no reliable literature among 230 million patients worldwide describing defective anti-viral immune responses in the upper respiratory tract, for instance against influenza A virus or against respiratory syncitial virus (RSV). We therefore re-examined the immune response to a human isolate of S. mansoni and challenged mice in the chronic phase of schistosomiasis with influenza A virus, or with pneumonia virus of mice (PVM), a mouse virus to model RSV infections. We found that mice with chronic schistosomiasis had significant, systemic immune responses induced by Th1, Th2, and Th17 helper cells. High serum levels of TNF-alpha, IFN-gamma, IL-5, IL-13, IL-2, IL-17, and GM-CSF were found after mating and oviposition. The lungs of diseased mice showed low-grade inflammation, with goblet cell hyperplasia and excessive mucus secretion, which was alleviated by treatment with an anti-TNF-alpha agent (Etanercept). Mice with chronic schistosomiasis were to a relative, but significant extent protected from a secondary viral respiratory challenge. The protection correlated with the onset of oviposition and TNF-alpha-mediated goblet cell hyperplasia and mucus secretion, suggesting that these mechanisms are involved in enhanced immune protection to respiratory viruses during chronic murine schistosomiasis. Indeed, also in a model of allergic airway inflammation mice were protected from a viral respiratory challenge with PVM.
Atherosclerosis is considered a chronic inflammatory disease of the arterial vessel wall which is not only modulated by innate and adaptive immune responses but also by factors of the blood coagulation system.
In general hypercoagulability seems to increase the development and progression of experimental atherosclerosis in mice on an atherogenic background. In addition, the great majority of coagulation proteins including coagulation factor XII (FXII) have been detected in early and advanced human atherosclerotic lesions supporting the cross-link between the coagulation system and atherosclerosis. Moreover, FXII has been detected in close proximity to macrophages, foam cells and smooth muscle cells in these lesions and has been demonstrated to be functionally active in human plaques. Although these data indicate that factor XII may play a role in atherogenesis a direct contribution of FXII to atherogenesis has not been addressed experimentally to date. Furthermore, clinical studies examining the function of FXII in vascular disease have yielded conflicting results.
Hence, in order to investigate the function of coagulation factor XII in atherosclerosis apolipoprotein E and FXII-deficient (F12\(^{-/-}\) apoE\(^{-/-}\)) mice were employed. Compared to F12\(^{+/+}\)apoE\(^{-/-}\) controls, atherosclerotic lesion formation was reduced in F12\(^{-/-}\)apoE\(^{-/-}\) mice, associated with diminished systemic T-cell activation and Th1-cell polarization after 12 weeks of high fat diet. Moreover, a significant decrease in plasma levels of complement factor C5a was evidenced in F12\(^{-/-}\)apoE\(^{-/-}\) mice. Interestingly, C5a increased the production of interleukin-12 (IL-12) in dendritic cells (DCs) and enhanced their capacity to trigger antigen-specific interferon-gamma (IFNγ) production in OTII CD4\(^+\) T cells in vitro. Importantly, a reduction in frequencies of IL-12 expressing splenic DCs from atherosclerotic F12\(^{-/-}\)apoE\(^{-/-}\) versus F12\(^{+/+}\)apoE\(^{-/-}\) mice was observed in vivo, accompanied by a diminished splenic Il12 transcript expression and significantly reduced IL-12 serum levels.
Consequently, these data reveal FXII to play an important role in atherosclerotic lesion formation and to promote DC-induced and systemic IL 12 expression as well as pro-inflammatory T-cell responses likely at least in part via the activation of the complement system.
Thymus-derived natural Foxp3\(^{+}\) CD4\(^{+}\) regulatory T cells (nTregs) play a key role in maintaining immune tolerance and preventing autoimmune disease. Several studies indicate that dendritic cells (DCs) are critically involved in the maintenance and proliferation of nTregs. However, the mechanisms how DCs manage to keep the peripheral pool at constant levels remain poorly understood. Here, we describe that the NF-κB/Rel family transcription factor RelB controls the frequencies of steady-state migratory DCs (ssmDCs) in peripheral lymph nodes and their numbers control peripheral nTreg homeostasis. DC-specific RelB depletion was investigated in CD11c-Cre × RelB\(^{fl/fl}\) mice (RelB\(^{DCko}\)), which showed normal frequencies of resident DCs in lymph nodes and spleen while the subsets of CD103\(^{-}\) Langerin\(^{-}\) dermal DCs (dDCs) and Langerhans cells but not CD103\(^{+}\) Langerin\(^{+}\) dDC of the ssmDCs in skin-draining lymph nodes were increased. Enhanced frequencies and proliferation rates were also observed for nTregs and a small population of CD4\(^{+}\) CD44\(^{high}\) CD25\(^{low}\) memory-like T cells (Tml). Interestingly, only the Tml but not DCs showed an increase in IL-2-producing capacity in lymph nodes of RelB\(^{DCko}\) mice. Blocking of IL-2 in vivo reduced the frequency of nTregs but increased the Tml frequencies, followed by a recovery of nTregs. Taken together, by employing RelB\(^{DCko}\) mice with increased frequencies of ssmDCs our data indicate a critical role for specific ssmDC subsets for the peripheral nTreg and IL-2\(^{+}\) Tml frequencies during homeostasis.
Immunotherapeutic strategies may be a treatment option in patients with refractory acute myelogenous leukemia (AML) or, in cases of complete remission after conventional therapy regimens, may help to reduce disease recurrence or delay time to progression. Evidence suggests a key role of dendritic cells (DCs) in cancer immunotherapy due to their capacity to present tumour antigens to effector cells. We generated cytokine-induced killer (CIK) cells from healthy donors and examined their responses in vitro in an LDH release assay against three cell lines and allogeneic HLA non-matched blasts from three patients with de novo AML after coincubation with autologous peripheral blood monocyte-derived DCs. Although DCs were unable to enhance CIK cell effects against all three cell lines tested, the cytotoxic activity against the patients’ AML cells increased after coculture with mature DCs, which was significant in two of three patients. However, neither prior pulsing of the DCs with blast cell lysates nor with leukemic cell-derived total RNA further enhanced the lytic capacity of the CIK cells. On the contrary, pulsing reduced or even reversed the cytotoxic activity of the effector cells. This decrease of allogeneic cytotoxicity led us to conclude that monocyte-derived DCs may be useful in autologous or allogeneic vaccine strategies for the treatment of AML or in priming donor lymphocytes in vitro, but unfractionated antigens as pulsing agents may have inhibitory effects on T cell efficiency and their employment in immunotherapeutic strategies for AML seems questionable.
Mature dendritic cells (DCs) represent cellular adjuvants for optimal antigen presentation in cancer vaccines. Recently, a combination of prostaglandin E\(_2\) (PGE\(_2\)) with Toll-like receptor agonists (TLR-P) was proposed as a new standard to generate superior cytokine-producing DCs with high migratory capacity. Here, we compare TLR-P DCs with conventional DCs matured only with the proinflammatory cytokines TNFα and IL-1ß (CDCs), focussing on the interaction of resulting DCs with CD8\(^+\) T-cells. TLR-P matured DCs showed elevated expression of activation markers such as CD80 and CD83 compared to CDCs, together with a significantly higher migration capacity. Secretion of IL-6, IL-8, IL-10, and IL-12 was highest after 16 h in TLR-P DCs, and only TLR-P DCs secreted active IL-12p70. TLR-P DCs as well as CDCs successfully primed multifunctional CD8\(^+\) T-cells from naïve precursors specific for the peptide antigens Melan-A, NLGN4X, and PTP with comparable priming efficacy and T-cell receptor avidity. CD8\(^+\) T-cells primed by TLR-P DCs showed significantly elevated expression of the integrin VLA-4 and a trend for higher T-cell numbers after expansion. In contrast, TLR-P DCs displayed a substantially reduced capability to cross-present CMVpp65 protein antigen to pp65-specific T cells, an effect that was dose-dependent on PGE2 during DC maturation and reproducible with several responder T-cell lines. In conclu-sion, TLR-P matured DCs might be optimal presenters of antigens not requiring processing such as short peptides. However, PGE\(_2\) seems less favorable for maturation of DCs intended to process and cross-present more complex vaccine antigens such as lysates, proteins or long peptides.
Pentacyclic triterpenes from Cecropia telenitida with immunomodulatory activity on dendritic cells
(2013)
Pentacyclic triterpenes are a large family of plant metabolites that exhibit a wide array of biological activities. The genus Cecropia, which encompasses many plant species, has been used as traditional medicine for the treatment of inflammatory diseases and is known to produce many active pentacyclic triterpenes. In this study we investigated the chemical composition of a pentacyclic triterpene fraction from the roots of Cecropia telenitida Cuatrec., Urticaceae. A novel compound, which we termed yarumic acid, and four known molecules (serjanic acid, spergulagenic acid A, 20-hydroxy-ursolic acid and goreishic acid I) were isolated and characterised. In a dendritic cell (DC)-based assay, we demonstrated that non-toxic doses of these pentacyclic triterpenes inhibited the secretion of at least one of the proinflammatory cytokines tested (IL-1 beta, IL-12p40, IL-12p70, TNF-alpha). Spergulagenic acid A also inhibited nitric oxide production in lipopolysaccharide-stimulated dendritic cell. Serjanic acid and spergulagenic acid A, which were the most potent abundant compounds in the pentacyclic triterpene fraction, showed the most activity in the dendritic cell-based assay. These results show that all pentacyclic triterpenes might contribute to the anti-inflammatory activities of C. telenitida. Moreover, yarumic acid as well as the four known pentacyclic triterpenes, can be exploited as potential immunomodulatory/anti-inflammatory agents.
Background
Cutaneous leishmaniasis (CL) is a neglected tropical disease caused by protozoan parasites of the genus Leishmania. CL causes enormous suffering in many countries worldwide. There is no licensed vaccine against CL, and the chemotherapy options show limited efficacy and high toxicity. Localization of the parasites inside host cells is a barrier to most standard chemo- and immune-based interventions. Hence, novel drugs, which are safe, effective and readily accessible to third-world countries and/or drug delivery technologies for effective CL treatments are desperately needed.
Methodology/Principal
Findings Here we evaluated the antileishmanial properties and delivery potential of polyhexamethylene biguanide (PHMB; polyhexanide), a widely used antimicrobial and wound antiseptic, in the Leishmania model. PHMB showed an inherent antileishmanial activity at submicromolar concentrations. Our data revealed that PHMB kills Leishmania major (L. major) via a dual mechanism involving disruption of membrane integrity and selective chromosome condensation and damage. PHMB's DNA binding and host cell entry properties were further exploited to improve the delivery and immunomodulatory activities of unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODN). PHMB spontaneously bound CpG ODN, forming stable nanopolyplexes that enhanced uptake of CpG ODN, potentiated antimicrobial killing and reduced host cell toxicity of PHMB.
Conclusions
Given its low cost and long history of safe topical use, PHMB holds promise as a drug for CL therapy and delivery vehicle for nucleic acid immunomodulators.
Investigations of Measles virus regulation on activation and function of antigen presenting cells
(2008)
Interaction with dendritic cells (DCs) is considered as central to immunosuppression induced by viruses, including measles virus (MV). Commonly, viral infection of DCs abrogates their ability to promote T cell expansion, yet underlying mechanisms at a cellular level are undefined. It appears that MV-WTF infection modulate DCs morphology and dynamic adhesion on extra cellular matrix proteins such as FN or ICAM-1. By morphological criteria, WTF-DCs resembled LPS-DCs, associated with their mature phenotype also adhered less efficiently to the FN or ICAM-1 support. Reduced adhesion could not be explained by a lack of 1-integrin expression or activation. Similarly, MV-DCs strongly resembled LPS-DCs in that levels of focal adhesion kinase phosphorylated at Y397 were high and not further enhanced upon FN ligation. Fascin, a downstream effector of integrin signaling was highly upregulated in LPS-DCs and moderately in WTF-DCs, and differences in its subcellular distribution were not observed between both cell cultures. Apparently, however, fascin associated less efficiently with PKC in WTF-DCs then in LPS-DCs. In line with findings for murine DCs, high motility of mature human DCs was found to require expression of Rac-GTPases. Human LPS-DCs and more so, DC transfected to express constitutively active Rac1 were the most motile DC-species analysed, confirming that migration of human DC also involved Rac activity. The velocity of WTF-DCs on FN is below that of LPS-DCs, indicating that maturation induced by WTF may be insufficient to completely promote integrin signaling which leads to Rac activation. The organisation of MV-DC/T cell interfaces was consistent with that of functional immune synapses with regard to CD3 clustering, MHC class II surface recruitment and MTOC location. These analyses are based in the selection of stable conjugates. Subsequently, however, neither contacts nor calcium flux can be stabilised and sustained in the majority of MV-DC/T cell conjugates and only promoted abortive T cell activation. Formation of spatially organised IS in T cells requites, prolonged contact durations. Therefore, aberrant distribution patterns of CD3 in these structures, if occurring, are not likely to contribute to the type of contacts predominating for WTF-DC/T cell interactions. It is also likely that transient interactions of less than 2 minutes may if at all, not efficiently support viral transmission to T cells. Transient interactions are typically observed with immature DCs in the absence of antigen, but this is not likely to be relevant in our allogenic system, which includes SA-loaded WTF-DCs. Thus, MV-infected DCs retain activities required for initiating, but not sustaining T cell conjugation and activation. This is partially rescued if surface expression of the MV glycoproteins on DCs is abolished by infection with a recombinant MV encoding VSV G protein instead, indicating that these contribute directly to synapse destabilisation and thereby act as effectors of T cell inhibition.
The diploid, polymorphic yeast Candida albicans is one of the most important human pathogenic fungi. C. albicans can grow, proliferate and coexist as a commensal on or within the human host for a long time. However, alterations in the host environment can render C. albicans virulent. In this review, we describe the immunological cross-talk between C. albicans and the human innate immune system. We give an overview in form of pairs of human defense strategies including immunological mechanisms as well as general stressors such as nutrient limitation, pH, fever etc. and the corresponding fungal response and evasion mechanisms. Furthermore, Computational Systems Biology approaches to model and investigate these complex interactions are highlighted with a special focus on game-theoretical methods and agent-based models. An outlook on interesting questions to be tackled by Systems Biology regarding entangled defense and evasion mechanisms is given.
Dendritic cells (DCs) and macrophages (Mph) share many characteristics as components of the innate immune system. The criteria to classify the multitude of subsets within the mononuclear phagocyte system are currently phenotype, ontogeny, transcription patterns, epigenetic adaptations, and function. More recently, ontogenetic, transcriptional, and proteomic research approaches uncovered major developmental differences between Flt3L-dependent conventional DCs as compared with Mphs and monocyte-derived DCs (MoDCs), the latter mainly generated in vitro from murine bone marrow-derived DCs (BM-DCs) or human CD14\(^{+}\) peripheral blood monocytes. Conversely, in vitro GM-CSF-dependent monocyte-derived Mphs largely resemble MoDCs whereas tissue-resident Mphs show a common embryonic origin from yolk sac and fetal liver with Langerhans cells (LCs). The novel ontogenetic findings opened discussions on the terminology of DCs versus Mphs. Here, we bring forward arguments to facilitate definitions of BM-DCs, MoDCs, and LCs. We propose a group model of terminology for all DC subsets that attempts to encompass both ontogeny and function.
The development of two conventional dendritic cells (DC) subsets (cDC1 and cDC2) and the plasmacytoid DC (pDC) in vivo and in cultures of bone marrow (BM) cells is mediated by the growth factor Flt3L. However, little is known about the factors that direct the development of the individual DC subsets. Here, we describe the selective in vitro generation of murine ESAM\(^{low}\) CD103\(^{-}\) XCR1\(^{-}\) CD172a\(^{+}\) CD11b\(^{+}\) cDC2 from BM by treatment with a combination of Flt3L, LIF, and IL‐10 (collectively named as FL10). FL10 promotes common dendritic cell progenitors (CDP) proliferation in the cultures, similar to Flt3L and CDP sorted and cultured in FL10 generate exclusively cDC2. These cDC2 express the transcription factors Irf4, Klf4, and Notch2, and their growth is reduced using BM from Irf4\(^{-/-}\) mice, but the expression of Batf3 and Tcf4 is low. Functionally they respond to TLR3, TLR4, and TLR9 signals by upregulation of the surface maturation markers MHC II, CD80, CD86, and CD40, while they poorly secrete proinflammatory cytokines. Peptide presentation to TCR transgenic OT‐II cells induced proliferation and IFN‐γ production that was similar to GM‐CSF‐generated BM‐DC and higher than Flt3L‐generated DC. Together, our data support that FL10 culture of BM cells selectively promotes CDP‐derived ESAM\(^{low}\) cDC2 (cDC2B) development and survival in vitro.
Invasive aspergillosis (IA) is an infectious disease caused by the fungal pathogen Aspergillus fumigatus that mainly affects immunocompromised hosts. To investigate immune cell cross-talk during infection with A. fumigatus, we co-cultured natural killer (NK) cells and dendritic cells (DC) after stimulation with whole fungal structures, components of the fungal cell wall, fungal lysate or ligands for distinct fungal receptors. Both cell types showed activation after stimulation with fungal components and were able to transfer activation signals to the counterpart not stimulated cell type. Interestingly, DCs recognized a broader spectrum of fungal components and thereby initiated NK cell activation when those did not recognize fungal structures. These experiments highlighted the supportive function of DCs in NK cell activation. Furthermore, we focused on soluble DC mediated NK cell activation and showed that DCs stimulated with the TLR2/Dectin-1 ligand zymosan could maximally stimulate the expression of CD69 on NK cells. Thus, we investigated the influence of both receptors for zymosan, Dectin-1 and TLR2, which are highly expressed on DCs but show only minimal expression on NK cells. Specific focus was laid on the question whether Dectin-1 or TLR2 signaling in DCs is important for the secretion of soluble factors leading to NK cell activation. Our results show that Dectin-1 and TLR2 are negligible for NK cell activation. We conclude that besides Dectin-1 and TLR2 other receptors on DCs are able to compensate for the missing signal.
Atherosclerosis is the main underlying cause for cardiovascular events such as myocardial infarction and stroke and its development might be influenced by immune cells. Dendritic cells (DCs) bridge innate and adaptive immune responses by presenting antigens to T cells and releasing a variety of cytokines. Several subsets of DCs can be discriminated that engage specific transcriptional pathways for their development. Basic leucine zipper transcription factor ATF-like 3 (Batf3) is required for the development of classical CD8α\(^{+}\) and CD103\(^{+}\) DCs. By crossing mice deficient in Batf3 with atherosclerosis-prone low density lipoprotein receptor (Ldlr\(^{−/-}\))-deficient mice we here aimed to further address the contribution of Batf3-dependent CD8α\(^{+}\) and CD103\(^{+}\) antigen-presenting cells to atherosclerosis. We demonstrate that deficiency in Batf3 entailed mild effects on the immune response in the spleen but did not alter atherosclerotic lesion formation in the aorta or aortic root, nor affected plaque phenotype in low density lipoprotein receptor-deficient mice fed a high fat diet. We thus provide evidence that Batf3-dependent antigen-presenting cells do not have a prominent role in atherosclerosis.
G-protein–coupled receptor (GPCR) signaling is essential for the spatiotemporal control of leukocyte dynamics during immune responses. For efficient navigation through mammalian tissues, most leukocyte types express more than one GPCR on their surface and sense a wide range of chemokines and chemoattractants, leading to basic forms of leukocyte movement (chemokinesis, haptokinesis, chemotaxis, haptotaxis, and chemorepulsion). How leukocytes integrate multiple GPCR signals and make directional decisions in lymphoid and inflamed tissues is still subject of intense research. Many of our concepts on GPCR-controlled leukocyte navigation in the presence of multiple GPCR signals derive from in vitro chemotaxis studies and lower vertebrates. In this review, we refer to these concepts and critically contemplate their relevance for the directional movement of several leukocyte subsets (neutrophils, T cells, and dendritic cells) in the complexity of mouse tissues. We discuss how leukocyte navigation can be regulated at the level of only a single GPCR (surface expression, competitive antagonism, oligomerization, homologous desensitization, and receptor internalization) or multiple GPCRs (synergy, hierarchical and non-hierarchical competition, sequential signaling, heterologous desensitization, and agonist scavenging). In particular, we will highlight recent advances in understanding GPCR-controlled leukocyte navigation by intravital microscopy of immune cells in mice.
Understanding the mechanisms of early invasion and epithelial defense in opportunistic mold infections is crucial for the evaluation of diagnostic biomarkers and novel treatment strategies. Recent studies revealed unique characteristics of the immunopathology of mucormycoses. We therefore adapted an alveolar Transwell® A549/HPAEC bilayer model for the assessment of epithelial barrier integrity and cytokine response to Rhizopus arrhizus, Rhizomucor pusillus, and Cunninghamella bertholletiae. Hyphal penetration of the alveolar barrier was validated by 18S ribosomal DNA detection in the endothelial compartment. Addition of dendritic cells (moDCs) to the alveolar compartment led to reduced fungal invasion and strongly enhanced pro-inflammatory cytokine response, whereas epithelial CCL2 and CCL5 release was reduced. Despite their phenotypic heterogeneity, the studied Mucorales species elicited the release of similar cytokine patterns by epithelial and dendritic cells. There were significantly elevated lactate dehydrogenase concentrations in the alveolar compartment and epithelial barrier permeability for dextran blue of different molecular weights in Mucorales-infected samples compared to Aspergillus fumigatus infection. Addition of monocyte-derived dendritic cells further aggravated LDH release and epithelial barrier permeability, highlighting the influence of the inflammatory response in mucormycosis-associated tissue damage. An important focus of this study was the evaluation of the reproducibility of readout parameters in independent experimental runs. Our results revealed consistently low coefficients of variation for cytokine concentrations and transcriptional levels of cytokine genes and cell integrity markers. As additional means of model validation, we confirmed that our bilayer model captures key principles of Mucorales biology such as accelerated growth in a hyperglycemic or ketoacidotic environment or reduced epithelial barrier invasion upon epithelial growth factor receptor blockade by gefitinib. Our findings indicate that the Transwell® bilayer model provides a reliable and reproducible tool for assessing host response in mucormycosis.