Publications by authors named "Fabienne Tacchini-Cottier"

63 Publications

The Impact of Neutrophil Recruitment to the Skin on the Pathology Induced by Infection.

Front Immunol 2021 1;12:649348. Epub 2021 Mar 1.

Department of Biochemistry, WHO Collaborative Centre for Research and Training in Immunology, University of Lausanne, Lausanne, Switzerland.

(.) are obligate intracellular protozoan parasites that cause the leishmaniases, a spectrum of neglected infectious vector-borne diseases with a broad range of clinical manifestations ranging from local cutaneous, to visceral forms of the diseases. The parasites are deposited in the mammalian skin during the blood meal of an infected female phlebotomine sand fly. The skin is a complex organ acting as the first line of physical and immune defense against pathogens. Insults to skin integrity, such as that occurring during insect feeding, induces the local secretion of pro-inflammatory molecules generating the rapid recruitment of neutrophils. At the site of infection, skin keratinocytes play a first role in host defense contributing to the recruitment of inflammatory cells to the infected dermis, of which neutrophils are the first recruited cells. Although neutrophils efficiently kill various pathogens including , several species have developed mechanisms to survive in these cells. In addition, through their rapid release of cytokines, neutrophils modulate the skin microenvironment at the site of infection, a process shaping the subsequent development of the adaptive immune response. Neutrophils may also be recruited later on in unhealing forms of cutaneous leishmaniasis and to the spleen and liver in visceral forms of the disease. Here, we will review the mechanisms involved in neutrophil recruitment to the skin following infection focusing on the role of keratinocytes in this process. We will also discuss the distinct involvement of neutrophils in the outcome of leishmaniasis.
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http://dx.doi.org/10.3389/fimmu.2021.649348DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7957080PMC
March 2021

Evaluation of a New Topical Treatment for the Control of Cutaneous Leishmaniasis.

Microorganisms 2020 Nov 17;8(11). Epub 2020 Nov 17.

Department of Biochemistry, University of Lausanne, 1066 Epalinges, Switzerland.

() causes cutaneous leishmaniasis in the Old World. The infection mostly induces a localized lesion restricted to the sand fly bite. The costs and the side effects of current treatments render imperative the development of new therapies that are affordable and easy to administrate. Topical treatment would be the ideal option for the treatment of cutaneous leishmaniasis. MF29 is a 3-haloacetamidobenzoate that was shown in vitro to inhibit tubulin assembly in . Here, we tested a topical cream formulated with MF29. BALB/c mice were infected in the ear dermis with metacyclic promastigotes and once the lesion appeared, mice were treated with different concentrations of MF29 and compared to the control group treated with the cream used as the vehicle. We observed that topical application of MF29 reduced the progression of the infection while control groups developed an unhealing lesion that became necrotic. The treatment decreased the type 2 immune response. Comparison with SinaAmphoLeish, another topical treatment, revealed that MF29 treatment once a day was sufficient to control lesion development, while application SinaAmphoLeish needed applications twice daily. Collectively, our data suggest that MF-29 topical application could be a promising topical treatment for cutaneous leishmaniasis.
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http://dx.doi.org/10.3390/microorganisms8111803DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7696824PMC
November 2020

TLR7 Sensing by Neutrophils Is Critical for the Control of Cutaneous Leishmaniasis.

Cell Rep 2020 06;31(10):107746

Department of Biochemistry, WHO-Immunology Research and Training Collaborative Centre, University of Lausanne, Epalinges, Vaud, Switzerland. Electronic address:

Neutrophils are rapidly recruited to sites of infection, where they kill invading pathogens. However, they may also act as early temporary shelters, favoring subsequent pathogen dissemination in the host. We find that TLR7 sensing of the protozoan Leishmania parasite in neutrophils is essential for early parasite load regulation. Neutrophil effector functions, including reactive oxygen species (ROS) and neutrophil extracellular trap formation, are decreased in the absence of TLR7, resulting in higher parasite load and selective parasite replication in Tlr7 neutrophils. Leishmania-infected Tlr7 mice develop a chronic unhealing lesion, despite Th1 cell differentiation, and we show that Tlr7 neutrophils alone mediate this effect. Conversely, topical treatment with a TLR7 agonist early in infection induces smaller lesion development than in untreated mice. Collectively, these findings highlight that parasite TLR7 triggering in neutrophils regulates early innate functions with major consequences on subsequent disease evolution, opening avenues for possible treatment strategies.
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http://dx.doi.org/10.1016/j.celrep.2020.107746DOI Listing
June 2020

M2-like, dermal macrophages are maintained via IL-4/CCL24-mediated cooperative interaction with eosinophils in cutaneous leishmaniasis.

Sci Immunol 2020 04;5(46)

Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.

Tissue-resident macrophages (TRMs) maintain tissue homeostasis, but they can also provide a replicative niche for intracellular pathogens such as How dermal TRMs proliferate and maintain their M2 properties even in the strong T1 environment of the infected dermis is not clear. Here, we show that, in infected mice lacking IL-4/13 from eosinophils, dermal TRMs shifted to a proinflammatory state, their numbers declined, and disease was attenuated. Intravital microscopy revealed a rapid infiltration of eosinophils followed by their tight interaction with dermal TRMs. IL-4-stimulated dermal TRMs, in concert with IL-10, produced a large amount of CCL24, which functioned to amplify eosinophil influx and their interaction with dermal TRMs. An intraperitoneal helminth infection model also demonstrated a requirement for eosinophil-derived IL-4 to maintain tissue macrophages through a CCL24-mediated amplification loop. CCL24 secretion was confined to resident macrophages in other tissues, implicating eosinophil-TRM cooperative interactions in diverse inflammatory settings.
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http://dx.doi.org/10.1126/sciimmunol.aaz4415DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7385908PMC
April 2020

Resistance of to Meglumine Antimoniate or Miltefosine Modulates Neutrophil Effector Functions.

Front Immunol 2018 21;9:3040. Epub 2018 Dec 21.

Department of Biochemistry, WHO-Immunology Research and Training Center, University of Lausanne, Epalinges, Switzerland.

is the main causative agent of cutaneous leishmaniasis in Colombia and is usually treated with either meglumine antimoniate (MA) or miltefosine (MIL). In recent years, there has been increasing evidence of the emergence of drug-resistance against these compounds. Neutrophils are known to play an important role in immunity against . These cells are rapidly recruited upon infection and are also present in chronic lesions. However, their involvement in the outcome of infection with drug-resistant has not been examined. In this study, human and murine neutrophils were infected with MA or MIL drug-resistant . lines derived from a parental . drug-susceptible strain. Neutrophil effector functions were assessed analyzing the production of reactive oxygen species (ROS), the formation of neutrophil extracellular trap (NET) and the expression of cell surface activation markers. Parasite killing by neutrophils was assessed using . transfected with a luciferase reporter. We show here that MA and MIL-resistant . lines elicited significantly increased NET formation and MA-resistant . induced significantly increased ROS production in both murine and human neutrophils, compared to infections with the parental MIL and MA susceptible strain. Furthermore, neutrophils exposed to drug-resistant lines showed increased activation, as revealed by decreased expression of CD62L and increased expression of CD66b in human neutrophils yet presented higher survival within neutrophils than the drug-susceptible strain. These results provide evidence that parasite drug-susceptibility may influences neutrophil activation and function as well as parasite survival within neutrophils. Further investigaton of the inter-relationship of drug susceptibility and neutrophil effector function should contribute to better understanding of the factors involved in susceptibility to anti- drugs.
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http://dx.doi.org/10.3389/fimmu.2018.03040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6308327PMC
October 2019

TLR2 Signaling in Skin Nonhematopoietic Cells Induces Early Neutrophil Recruitment in Response to Leishmania major Infection.

J Invest Dermatol 2019 06 27;139(6):1318-1328. Epub 2018 Dec 27.

Department of Biochemistry, Faculty of Biology and Medicine, University of Lausanne, Epalinges, Switzerland; World Health Organization Immunology Research and Training Center, Faculty of Biology and Medicine, University of Lausanne, Epalinges, Switzerland. Electronic address:

Neutrophils are rapidly recruited to the mammalian skin in response to infection with the cutaneous Leishmania pathogen. The parasites use neutrophils to establish the disease; however, the signals driving early neutrophil recruitment are poorly known. Here, we identified the functional importance of TLR2 signaling in this process. Using bone marrow chimeras and immunohistology, we identified the TLR2-expressing cells involved in this early neutrophil recruitment to be of nonhematopoietic origin. Keratinocytes are damaged and briefly in contact with the parasites during infection. We show that TLR2 triggering by Leishmania major is required for their secretion of neutrophil-attracting chemokines. Furthermore, TLR2 triggering by L. major phosphoglycans is critical for neutrophil recruitment to negatively affect disease development, as shown by better control of lesion size and parasite load in Tlr2 compared with wild-type infected mice. Conversely, restoring early neutrophil presence in Tlr2 mice through injection of wild-type neutrophils or CXCL1 at the onset of infection resulted in delayed disease resolution comparable to that observed in wild-type mice. Taken together, our data show a crucial role for TLR2-expressing nonhematopoietic skin cells in the recruitment of the first wave of neutrophils after L. major infection, a process that delays disease control.
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http://dx.doi.org/10.1016/j.jid.2018.12.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8024985PMC
June 2019

Deletion of Interleukin-4 Receptor Alpha-Responsive Keratinocytes in BALB/c Mice Does Not Alter Susceptibility to Cutaneous Leishmaniasis.

Infect Immun 2018 12 20;86(12). Epub 2018 Nov 20.

International Center for Genetic Engineering and Biotechnology (ICGEB), Cape Town Component, Cape Town, South Africa

The skin microenvironment at the site of infection plays a role in the early events that determine protective T helper 1/type 1 immune responses during cutaneous leishmaniasis (CL) infection. During CL in nonhealing BALB/c mice, early interleukin-4 (IL-4) can instruct dendritic cells for protective Th1 immunity. Additionally, keratinocytes, which are the principal cell type in the skin epidermis, have been shown to secrete IL-4 early after infection. Here, we investigated whether IL-4/IL-13 signaling via the common IL-4 receptor alpha chain (IL-4Rα) on keratinocytes contributes to susceptibility during experimental CL. To address this, keratinocyte-specific IL-4Rα-deficient (KRT14 IL-4Rα) mice on a BALB/c genetic background were generated by gene targeting and site-specific recombination (Cre/) under the control of the keratinocyte-specific locus. Following high-dose infection with IL-81 and LV39 promastigotes subcutaneously in the footpad, footpad swelling, parasite burden, IFN-γ/IL-4/IL-13 cytokine production, and type 1 and type 2 antibody responses were similar between KRT14 IL-4Rα and littermate control IL-4Rα BALB/c mice. An intradermal infection with low-dose IL-81 and LV39 promastigotes in the ear showed results in infected KRT14 IL-4Rα BALB/c mice similar to those of littermate control IL-4Rα BALB/c mice, with the exception of a significant decrease observed in parasite burden only at the site of LV39 infection in the ear. Collectively, our results show that autocrine and paracrine signaling of IL-4/IL-13 through the IL-4Rα chain on keratinocytes does not influence the establishment of a nonhealing Th2 immune response in BALB/c mice during infection.
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http://dx.doi.org/10.1128/IAI.00710-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6246911PMC
December 2018

Neutrophils enhance early Trypanosoma brucei infection onset.

Sci Rep 2018 07 25;8(1):11203. Epub 2018 Jul 25.

Unit of Veterinary Protozoology, Department of Biomedical Sciences, Institute of Tropical Medicine Antwerp (ITM), Antwerp, Belgium.

In this study, Trypanosoma brucei was naturally transmitted to mice through the bites of infected Glossina morsitans tsetse flies. Neutrophils were recruited rapidly to the bite site, whereas monocytes were attracted more gradually. Expression of inflammatory cytokines (il1b, il6), il10 and neutrophil chemokines (cxcl1, cxcl5) was transiently up-regulated at the site of parasite inoculation. Then, a second influx of neutrophils occurred that coincided with the previously described parasite retention and expansion in the ear dermis. Congenital and experimental neutropenia models, combined with bioluminescent imaging, indicate that neutrophils do not significantly contribute to dermal parasite control and elicit higher systemic parasitemia levels during the infection onset. Engulfment of parasites by neutrophils in the skin was rarely observed and was restricted to parasites with reduced motility/viability, whereas live parasites escaped phagocytosis. To our knowledge, this study represents the first description of a trypanosome infection promoting role of early innate immunological reactions following an infective tsetse fly bite. Our data indicate that the trypanosome is not hindered in its early development and benefits from the host innate responses with the neutrophils being important regulators of the early infection, as already demonstrated for the sand fly transmitted Leishmania parasite.
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http://dx.doi.org/10.1038/s41598-018-29527-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6060092PMC
July 2018

Survival Mechanisms Used by Some Species to Escape Neutrophil Killing.

Front Immunol 2017 16;8:1558. Epub 2017 Nov 16.

Department of Biochemistry, WHO Immunology Research and Training Collaborative Center, University of Lausanne, Lausanne, Switzerland.

Neutrophils are the most abundant leukocytes in human blood. Upon microbial infection, they are massively and rapidly recruited from the circulation to sites of infection where they efficiently kill pathogens. To this end, neutrophils possess a variety of weapons that can be mobilized and become effective within hours following infection. However, several microbes including some spp. have evolved a variety of mechanisms to escape neutrophil killing using these cells as a basis to better invade the host. In addition, neutrophils are also present in unhealing cutaneous lesions where their role remains to be defined. Here, we will review recent progress in the field and discuss the different strategies applied by some parasites to escape from being killed by neutrophils and as recently described for , even replicate within these cells. Subversion of neutrophil killing functions by is a strategy that allows parasite spreading in the host with a consequent deleterious impact, transforming the primary protective role of neutrophils into a deleterious one.
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http://dx.doi.org/10.3389/fimmu.2017.01558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5715327PMC
November 2017

IL-4Rα Signaling in Keratinocytes and Early IL-4 Production Are Dispensable for Generating a Curative T Helper 1 Response in -Infected C57BL/6 Mice.

Front Immunol 2017 10;8:1265. Epub 2017 Oct 10.

Department of Biochemistry, WHO-Immunology Research and Training Center, University of Lausanne, Lausanne, Switzerland.

Experimental infection with the protozoan parasite has been extensively used to understand the mechanisms involved in T helper cell differentiation. Following infection, C57BL/6 mice develop a small self-healing cutaneous lesion and they are able to control parasite burden, a process linked to the development of T helper (Th) 1 cells. The local presence of IL-12 has been reported to be critical in driving Th1 cell differentiation. In addition, the early secretion of IL-4 was reported to potentially contribute to Th1 cell differentiation. Following infection with , early keratinocyte-derived IL-4 was suggested to contribute to Th1 cell differentiation. To investigate a putative autocrine role of IL-4 signaling on keratinocytes at the site of infection, we generated C57BL/6 mice deficient for IL-4Rα expression selectively in keratinocytes. Upon infection with , these mice could control their inflammatory lesion and parasite load correlating with the development of Th1 effector cells. These data demonstrate that IL-4 signaling on keratinocytes does not contribute to Th1 cell differentiation. To further investigate the source of IL-4 in the skin during the first days after infection, we used C57BL/6 IL-4 reporter mice allowing the visualization of IL-4 mRNA expression and protein production. These mice were infected with . During the first 3 days after infection, skin IL-4 mRNA expression was observed selectively in mast cells. However, no IL-4 protein production was detectable locally. In addition, early IL-4 blockade locally had no impact on subsequent Th1 cell differentiation and control of the disease. Taken together, the present data rule out a major role for skin IL-4 and keratinocyte IL-4Rα signaling in the development of a Th1 protective immune response following experimental infection with .
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http://dx.doi.org/10.3389/fimmu.2017.01265DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5641309PMC
October 2017

Targeting Prolyl-tRNA Synthetase to Accelerate Drug Discovery against Malaria, Leishmaniasis, Toxoplasmosis, Cryptosporidiosis, and Coccidiosis.

Structure 2017 10 31;25(10):1495-1505.e6. Epub 2017 Aug 31.

Molecular Medicine - Structural Parasitology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, New Delhi 110067, India. Electronic address:

Developing anti-parasitic lead compounds that act on key vulnerabilities are necessary for new anti-infectives. Malaria, leishmaniasis, toxoplasmosis, cryptosporidiosis and coccidiosis together kill >500,000 humans annually. Their causative parasites Plasmodium, Leishmania, Toxoplasma, Cryptosporidium and Eimeria display high conservation in many housekeeping genes, suggesting that these parasites can be attacked by targeting invariant essential proteins. Here, we describe selective and potent inhibition of prolyl-tRNA synthetases (PRSs) from the above parasites using a series of quinazolinone-scaffold compounds. Our PRS-drug co-crystal structures reveal remarkable active site plasticity that accommodates diversely substituted compounds, an enzymatic feature that can be leveraged for refining drug-like properties of quinazolinones on a per parasite basis. A compound we termed In-5 exhibited a unique double conformation, enhanced drug-like properties, and cleared malaria in mice. It thus represents a new lead for optimization. Collectively, our data offer insights into the structure-guided optimization of quinazolinone-based compounds for drug development against multiple human eukaryotic pathogens.
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http://dx.doi.org/10.1016/j.str.2017.07.015DOI Listing
October 2017

Frontline Science: amastigotes can replicate within neutrophils.

J Leukoc Biol 2017 11 10;102(5):1187-1198. Epub 2017 Aug 10.

Department of Biochemistry, World Health Organization-Immunology Research and Training Collaborative Center, University of Lausanne, Epalinges, Switzerland; and

Cutaneous leishmaniasis is a neglected tropical disease, causing a spectrum of clinical manifestations varying from self-healing to unhealing lesions that may be very difficult to treat. Emerging evidence points to a detrimental role for neutrophils during the first hours following infection with many distinct species (spp.) at a time when the parasite is in its nonreplicative promastigote form. Neutrophils have also been detected at later stages of infection in unhealing chronic cutaneous lesions. However, the interactions between these cells and the replicative intracellular amastigote form of the parasite have been poorly studied. Here, we show that amastigotes are efficiently internalized by neutrophils and that this process has only a low impact on neutrophil activation and apoptosis. In neutrophils, the amastigotes were found in acidified vesicles. Furthermore, within cutaneous unhealing lesions, heavily infected neutrophils were found with up to 6 parasites per cell. To investigate if the amastigotes could replicate within neutrophils, we generated photoconvertible fluorescent parasites. With the use of flow cytometry imaging and time-lapse microscopy, we could demonstrate that a subset of parasites replicated within neutrophils. Overall, our data reveal a novel role for neutrophils that can act as a niche for parasite replication during the chronic phase of infection, thereby contributing to disease pathology.
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http://dx.doi.org/10.1189/jlb.4HI0417-158RDOI Listing
November 2017

Notch regulates Th17 differentiation and controls trafficking of IL-17 and metabolic regulators within Th17 cells in a context-dependent manner.

Sci Rep 2016 12 15;6:39117. Epub 2016 Dec 15.

Department of Biochemistry, WHO-Immunology Research and Training Center, University of Lausanne, Switzerland.

Th17 cells play critical roles in host defense and autoimmunity. Emerging data support a role for Notch signaling in Th17 cell differentiation but whether it is a positive or negative regulator remains unclear. We report here that T cell-specific deletion of Notch receptors enhances Th17 cell differentiation in the gut, with a corresponding increase in IL-17 secretion. An increase in Th17 cell frequency was similarly observed following immunization of T cell specific Notch mutant mice with OVA/CFA. However, in this setting, Th17 cytokine secretion was impaired, and increased intracellular retention of IL-17 was observed. Intracellular IL-17 co-localized with the CD71 iron transporter in the draining lymph node of both control and Notch-deficient Th17 cells. Immunization induced CD71 surface expression in control, but not in Notch-deficient Th17 cells, revealing defective CD71 intracellular transport in absence of Notch signaling. Moreover, Notch receptor deficient Th17 cells had impaired mTORC2 activity. These data reveal a context-dependent impact of Notch on vesicular transport during high metabolic demand suggesting a role for Notch signaling in the bridging of T cell metabolic demands and effector functions. Collectively, our findings indicate a prominent regulatory role for Notch signaling in the fine-tuning of Th17 cell differentiation and effector function.
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http://dx.doi.org/10.1038/srep39117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5156918PMC
December 2016

Notch Signaling Regulates the Homeostasis of Tissue-Restricted Innate-like T Cells.

J Immunol 2016 08 20;197(3):771-82. Epub 2016 Jun 20.

Ludwig Centre for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland;

Although Notch signaling plays important roles in lineage commitment and differentiation of multiple cell types including conventional T cells, nothing is currently known concerning Notch function in innate-like T cells. We have found that the homeostasis of several well-characterized populations of innate-like T cells including invariant NKT cells (iNKT), CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells is controlled by Notch. Notch selectively regulates hepatic iNKT cell survival via tissue-restricted control of B cell lymphoma 2 and IL-7Rα expression. More generally, Notch regulation of innate-like T cell homeostasis involves both cell-intrinsic and -extrinsic mechanisms and relies upon context-dependent interactions with Notch ligand-expressing fibroblastic stromal cells. Collectively, using conditional ablation of Notch receptors on peripheral T cells or Notch ligands on putative fibroblastic stromal cells, we show that Notch signaling is indispensable for the homeostasis of three tissue-restricted populations of innate-like T cells: hepatic iNKT, CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells, thus supporting a generalized role for Notch in innate T cell homeostasis.
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http://dx.doi.org/10.4049/jimmunol.1501675DOI Listing
August 2016

Different Leishmania Species Drive Distinct Neutrophil Functions.

Trends Parasitol 2016 05 1;32(5):392-401. Epub 2016 Mar 1.

Department of Biochemistry, WHO-IRTC, University of Lausanne, Lausanne, Switzerland. Electronic address:

Leishmaniases are vector-borne diseases of serious public health importance. During a sand fly blood meal, Leishmania parasites are deposited in the host dermis where neutrophils are rapidly recruited. Neutrophils are the first line of defense and can kill pathogens by an array of mechanisms. They can also form web-like structures called neutrophil extracellular traps (NETs) that can trap and/or kill microbes. The function of neutrophils in leishmaniasis was reported to be either beneficial by contributing to parasite killing or detrimental by impairing immune response development and control of parasite load. Here we review recent data showing that different Leishmania species elicit distinct neutrophil functions thereby influencing disease outcomes. Emerging evidence suggests that neutrophils should be considered important modulators of leishmaniasis.
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http://dx.doi.org/10.1016/j.pt.2016.02.003DOI Listing
May 2016

The Nlrp3 inflammasome, IL-1β, and neutrophil recruitment are required for susceptibility to a nonhealing strain of Leishmania major in C57BL/6 mice.

Eur J Immunol 2016 Apr 20;46(4):897-911. Epub 2016 Jan 20.

Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.

Infection of C57BL/6 mice with most Leishmania major strains results in a healing lesion and clearance of parasites from the skin. Infection of C57BL/6 mice with the L. major Seidman strain (LmSd), isolated from a patient with chronic lesions, despite eliciting a strong Th1 response, results in a nonhealing lesion, poor parasite clearance, and complete destruction of the ear dermis. We show here that in comparison to a healing strain, LmSd elicited early upregulation of IL-1β mRNA and IL-1β-producing dermal cells and prominent neutrophil recruitment to the infected skin. Mice deficient in Nlrp3, apoptosis-associated speck-like protein containing a caspase recruitment domain, or caspase-1/11, or lacking IL-1β or IL-1 receptor signaling, developed healing lesions and cleared LmSd from the infection site. Mice resistant to LmSd had a stronger antigen-specific Th1 response. The possibility that IL-1β might act through neutrophil recruitment to locally suppress immunity was supported by the healing observed in neutropenic Genista mice. Secretion of mature IL-1β by LmSd-infected macrophages in vitro was dependent on activation of the Nlrp3 inflammasome and caspase-1. These data reveal that Nlrp3 inflammasome-dependent IL-1β, associated with localized neutrophil recruitment, plays a crucial role in the development of a nonhealing form of cutaneous leishmaniasis in conventionally resistant mice.
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http://dx.doi.org/10.1002/eji.201546015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4828310PMC
April 2016

NLRP12 is a neutrophil-specific, negative regulator of in vitro cell migration but does not modulate LPS- or infection-induced NF-κB or ERK signalling.

Immunobiology 2016 Feb 23;221(2):341-6. Epub 2015 Oct 23.

Institute for Molecular Bioscience, University of Queensland, St Lucia 4072, Australia. Electronic address:

NOD-like receptors (NLR) are a family of cytosolic pattern recognition receptors that include many key drivers of innate immune responses. NLRP12 is an emerging member of the NLR family that is closely related to the well-known inflammasome scaffold, NLRP3. Since its discovery, various functions have been proposed for NLRP12, including the positive regulation of dendritic cell (DC) and neutrophil migration and the inhibition of NF-κB and ERK signalling in DC and macrophages. We show here that NLRP12 is poorly expressed in murine macrophages and DC, but is strongly expressed in neutrophils. Using myeloid cells from WT and Nlrp12(-/)(-) mice, we show that, contrary to previous reports, NLRP12 does not suppress LPS- or infection-induced NF-κB or ERK activation in myeloid cells, and is not required for DC migration in vitro. Surprisingly, we found that Nlrp12 deficiency caused increased rather than decreased neutrophil migration towards the chemokine CXCL1 and the neutrophil parasite Leishmania major, revealing NLRP12 as a negative regulator of directed neutrophil migration under these conditions.
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http://dx.doi.org/10.1016/j.imbio.2015.10.001DOI Listing
February 2016

Rapid Sequestration of Leishmania mexicana by Neutrophils Contributes to the Development of Chronic Lesion.

PLoS Pathog 2015 May 28;11(5):e1004929. Epub 2015 May 28.

Department of Biochemistry, WHO-Immunology Research and Training Center, University of Lausanne, Epalinges, Switzerland.

The protozoan Leishmania mexicana parasite causes chronic non-healing cutaneous lesions in humans and mice with poor parasite control. The mechanisms preventing the development of a protective immune response against this parasite are unclear. Here we provide data demonstrating that parasite sequestration by neutrophils is responsible for disease progression in mice. Within hours of infection L. mexicana induced the local recruitment of neutrophils, which ingested parasites and formed extracellular traps without markedly impairing parasite survival. We further showed that the L. mexicana-induced recruitment of neutrophils impaired the early recruitment of dendritic cells at the site of infection as observed by intravital 2-photon microscopy and flow cytometry analysis. Indeed, infection of neutropenic Genista mice and of mice depleted of neutrophils at the onset of infection demonstrated a prominent role for neutrophils in this process. Furthermore, an increase in monocyte-derived dendritic cells was also observed in draining lymph nodes of neutropenic mice, correlating with subsequent increased frequency of IFNγ-secreting T helper cells, and better parasite control leading ultimately to complete healing of the lesion. Altogether, these findings show that L. mexicana exploits neutrophils to block the induction of a protective immune response and impairs the control of lesion development. Our data thus demonstrate an unanticipated negative role for these innate immune cells in host defense, suggesting that in certain forms of cutaneous leishmaniasis, regulating neutrophil recruitment could be a strategy to promote lesion healing.
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http://dx.doi.org/10.1371/journal.ppat.1004929DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4447405PMC
May 2015

Exposure to Leishmania braziliensis triggers neutrophil activation and apoptosis.

PLoS Negl Trop Dis 2015 Mar 10;9(3):e0003601. Epub 2015 Mar 10.

Centro de Pesquisas Gonçalo Moniz, FIOCRUZ, Salvador, Bahia, Brazil; Instituto de Investigação em Imunologia, Salvador, Bahia, Brazil.

Background: Neutrophils are the first line of defense against invading pathogens and are rapidly recruited to the sites of Leishmania inoculation. During Leishmania braziliensis infection, depletion of inflammatory cells significantly increases the parasite load whereas co-inoculation of neutrophils plus L. braziliensis had an opposite effect. Moreover, the co-culture of infected macrophages and neutrophils also induced parasite killing leading us to ask how neutrophils alone respond to an L. braziliensis exposure. Herein we focused on understanding the interaction between neutrophils and L. braziliensis, exploring cell activation and apoptotic fate.

Methods And Findings: Inoculation of serum-opsonized L. braziliensis promastigotes in mice induced neutrophil accumulation in vivo, peaking at 24 h. In vitro, exposure of thyoglycollate-elicited inflammatory or bone marrow neutrophils to L. braziliensis modulated the expression of surface molecules such as CD18 and CD62L, and induced the oxidative burst. Using mCherry-expressing L. braziliensis, we determined that such effects were mainly observed in infected and not in bystander cells. Neutrophil activation following contact with L. braziliensis was also confirmed by the release of TNF-α and neutrophil elastase. Lastly, neutrophils infected with L. braziliensis but not with L. major displayed markers of early apoptosis.

Conclusions: We show that L. braziliensis induces neutrophil recruitment in vivo and that neutrophils exposed to the parasite in vitro respond through activation and release of inflammatory mediators. This outcome may impact on parasite elimination, particularly at the early stages of infection.
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http://dx.doi.org/10.1371/journal.pntd.0003601DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354905PMC
March 2015

Blocking junctional adhesion molecule C enhances dendritic cell migration and boosts the immune responses against Leishmania major.

PLoS Pathog 2014 Dec 4;10(12):e1004550. Epub 2014 Dec 4.

Department of Pathology and Immunology, Centre Médical Universitaire, University of Geneva, Geneva, Switzerland.

The recruitment of dendritic cells to sites of infections and their migration to lymph nodes is fundamental for antigen processing and presentation to T cells. In the present study, we showed that antibody blockade of junctional adhesion molecule C (JAM-C) on endothelial cells removed JAM-C away from junctions and increased vascular permeability after L. major infection. This has multiple consequences on the output of the immune response. In resistant C57BL/6 and susceptible BALB/c mice, we found higher numbers of innate immune cells migrating from blood to the site of infection. The subsequent migration of dendritic cells (DCs) from the skin to the draining lymph node was also improved, thereby boosting the induction of the adaptive immune response. In C57BL/6 mice, JAM-C blockade after L. major injection led to an enhanced IFN-γ dominated T helper 1 (Th1) response with reduced skin lesions and parasite burden. Conversely, anti JAM-C treatment increased the IL-4-driven T helper 2 (Th2) response in BALB/c mice with disease exacerbation. Overall, our results show that JAM-C blockade can finely-tune the innate cell migration and accelerate the consequent immune response to L. major without changing the type of the T helper cell response.
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http://dx.doi.org/10.1371/journal.ppat.1004550DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4256467PMC
December 2014

Specific fibroblastic niches in secondary lymphoid organs orchestrate distinct Notch-regulated immune responses.

J Exp Med 2014 Oct 13;211(11):2265-79. Epub 2014 Oct 13.

Ecole Polytechnique Fédérale de Lausanne, School of Life Sciences, Swiss Experimental Cancer Research, 1015 Lausanne, Switzerland

Fibroblast-like cells of secondary lymphoid organs (SLO) are important for tissue architecture. In addition, they regulate lymphocyte compartmentalization through the secretion of chemokines, and participate in the orchestration of appropriate cell-cell interactions required for adaptive immunity. Here, we provide data demonstrating the functional importance of SLO fibroblasts during Notch-mediated lineage specification and immune response. Genetic ablation of the Notch ligand Delta-like (DL)1 identified splenic fibroblasts rather than hematopoietic or endothelial cells as niche cells, allowing Notch 2-driven differentiation of marginal zone B cells and of Esam(+) dendritic cells. Moreover, conditional inactivation of DL4 in lymph node fibroblasts resulted in impaired follicular helper T cell differentiation and, consequently, in reduced numbers of germinal center B cells and absence of high-affinity antibodies. Our data demonstrate previously unknown roles for DL ligand-expressing fibroblasts in SLO niches as drivers of multiple Notch-mediated immune differentiation processes.
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http://dx.doi.org/10.1084/jem.20132528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4203954PMC
October 2014

Activated group 3 innate lymphoid cells promote T-cell-mediated immune responses.

Proc Natl Acad Sci U S A 2014 Sep 18;111(35):12835-40. Epub 2014 Aug 18.

Department of Biomedicine, University of Basel, 4058 Basel, Switzerland; University Children's Hospital of Basel, 4056 Basel, Switzerland;

Group 3 innate lymphoid cells (ILC3s) have emerged as important cellular players in tissue repair and innate immunity. Whether these cells meaningfully regulate adaptive immune responses upon activation has yet to be explored. Here we show that upon IL-1β stimulation, peripheral ILC3s become activated, secrete cytokines, up-regulate surface MHC class II molecules, and express costimulatory molecules. ILC3s can take up latex beads, process protein antigen, and consequently prime CD4(+) T-cell responses in vitro. The cognate interaction of ILC3s and CD4(+) T cells leads to T-cell proliferation both in vitro and in vivo, whereas its disruption impairs specific T-cell and T-dependent B-cell responses in vivo. In addition, the ILC3-CD4(+) T-cell interaction is bidirectional and leads to the activation of ILC3s. Taken together, our data reveal a novel activation-dependent function of peripheral ILC3s in eliciting cognate CD4(+) T-cell immune responses.
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http://dx.doi.org/10.1073/pnas.1406908111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4156721PMC
September 2014

Cross-presenting dendritic cells are required for control of Leishmania major infection.

Eur J Immunol 2014 May 25;44(5):1422-32. Epub 2014 Mar 25.

Department of Biochemistry, University of Lausanne, Lausanne, Switzerland.

Leishmania major infection induces self-healing cutaneous lesions in C57BL/6 mice. Both IL-12 and IFN-γ are essential for the control of infection. We infected Jun dimerization protein p21SNFT (Batf3(-/-) ) mice (C57BL/6 background) that lack the major IL-12 producing and cross-presenting CD8α(+) and CD103(+) DC subsets. Batf3(-/-) mice displayed enhanced susceptibility with larger lesions and higher parasite burden. Additionally, cells from draining lymph nodes of infected Batf3(-/-) mice secreted less IFN-γ, but more Th2- and Th17-type cytokines, mirrored by increased serum IgE and Leishmania-specific immunoglobulin 1 (Th2 indicating). Importantly, CD8α(+) DCs isolated from lymph nodes of L. major-infected mice induced significantly more IFN-γ secretion by L. major-stimulated immune T cells than CD103(+) DCs. We next developed CD11c-diptheria toxin receptor: Batf3(-/-) mixed bone marrow chimeras to determine when the DCs are important for the control of infection. Mice depleted of Batf-3-dependent DCs from day 17 or wild-type mice depleted of cross-presenting DCs from 17-19 days after infection maintained significantly larger lesions similar to mice whose Batf-3-dependent DCs were depleted from the onset of infection. Thus, we have identified a crucial role for Batf-3-dependent DCs in protection against L. major.
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http://dx.doi.org/10.1002/eji.201344242DOI Listing
May 2014

TREM-1 deficiency can attenuate disease severity without affecting pathogen clearance.

PLoS Pathog 2014 Jan 16;10(1):e1003900. Epub 2014 Jan 16.

Division of Experimental Pathology, Institute of Pathology, University of Bern, Bern, Switzerland.

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune reactions. While TREM-1-amplified responses likely aid an improved detection and elimination of pathogens, excessive production of cytokines and oxygen radicals can also severely harm the host. Studies addressing the pathogenic role of TREM-1 during endotoxin-induced shock or microbial sepsis have so far mostly relied on the administration of TREM-1 fusion proteins or peptides representing part of the extracellular domain of TREM-1. However, binding of these agents to the yet unidentified TREM-1 ligand could also impact signaling through alternative receptors. More importantly, controversial results have been obtained regarding the requirement of TREM-1 for microbial control. To unambiguously investigate the role of TREM-1 in homeostasis and disease, we have generated mice deficient in Trem1. Trem1(-/-) mice are viable, fertile and show no altered hematopoietic compartment. In CD4(+) T cell- and dextran sodium sulfate-induced models of colitis, Trem1(-/-) mice displayed significantly attenuated disease that was associated with reduced inflammatory infiltrates and diminished expression of pro-inflammatory cytokines. Trem1(-/-) mice also exhibited reduced neutrophilic infiltration and decreased lesion size upon infection with Leishmania major. Furthermore, reduced morbidity was observed for influenza virus-infected Trem1(-/-) mice. Importantly, while immune-associated pathologies were significantly reduced, Trem1(-/-) mice were equally capable of controlling infections with L. major, influenza virus, but also Legionella pneumophila as Trem1(+/+) controls. Our results not only demonstrate an unanticipated pathogenic impact of TREM-1 during a viral and parasitic infection, but also indicate that therapeutic blocking of TREM-1 in distinct inflammatory disorders holds considerable promise by blunting excessive inflammation while preserving the capacity for microbial control.
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http://dx.doi.org/10.1371/journal.ppat.1003900DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3894224PMC
January 2014

Repeated exposure to Lutzomyia intermedia sand fly saliva induces local expression of interferon-inducible genes both at the site of injection in mice and in human blood.

PLoS Negl Trop Dis 2014 9;8(1):e2627. Epub 2014 Jan 9.

Department of Biochemistry, and WHO-Immunology Research and Training Center, University of Lausanne, Epalinges, Switzerland.

During a blood meal, Lutzomyia intermedia sand flies transmit Leishmania braziliensis, a parasite causing tegumentary leishmaniasis. In experimental leishmaniasis, pre-exposure to saliva of most blood-feeding sand flies results in parasite establishment in absence of any skin damages in mice challenged with dermotropic Leishmania species together with saliva. In contrast, pre-immunization with Lu. intermedia salivary gland sonicate (SGS) results in enhanced skin inflammatory exacerbation upon co-inoculation of Lu. intermedia SGS and L. braziliensis. These data highlight potential unique features of both L. braziliensis and Lu. intermedia. In this study, we investigated the genes modulated by Lu. intermedia SGS immunization to understand their potential impact on the subsequent cutaneous immune response following inoculation of both SGS and L. braziliensis. The cellular recruitment and global gene expression profile was analyzed in mice repeatedly inoculated or not with Lu. intermedia. Microarray gene analysis revealed the upregulation of a distinct set of IFN-inducible genes, an immune signature not seen to the same extent in control animals. Of note this INF-inducible gene set was not induced in SGS pre-immunized mice subsequently co-inoculated with SGS and L. braziliensis. These data suggest the parasite prevented the upregulation of this Lu. intermedia saliva-related immune signature. The presence of these IFN-inducible genes was further analyzed in peripheral blood mononuclear cells (PBMCs) sampled from uninfected human individuals living in a L. braziliensis-endemic region of Brazil thus regularly exposed to Lu. intermedia bites. PBMCs were cultured in presence or absence of Lu. intermedia SGS. Using qRT-PCR we established that the IFN-inducible genes induced in the skin of SGS pre-immunized mice, were also upregulated by SGS in PBMCs from human individuals regularly exposed to Lu. intermedia bites, but not in PBMCs of control subjects. These data demonstrate that repeated exposure to Lu. intermedia SGS induces the expression of potentially host-protective IFN-inducible genes.
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http://dx.doi.org/10.1371/journal.pntd.0002627DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3888461PMC
September 2014

Trapping of naive lymphocytes triggers rapid growth and remodeling of the fibroblast network in reactive murine lymph nodes.

Proc Natl Acad Sci U S A 2014 Jan 23;111(1):E109-18. Epub 2013 Dec 23.

Department of Biochemistry and World Health Organization Immunology Research and Training Center, University of Lausanne, 1066 Epalinges, Switzerland.

Adaptive immunity is initiated in T-cell zones of secondary lymphoid organs. These zones are organized in a rigid 3D network of fibroblastic reticular cells (FRCs) that are a rich cytokine source. In response to lymph-borne antigens, draining lymph nodes (LNs) expand several folds in size, but the fate and role of the FRC network during immune response is not fully understood. Here we show that T-cell responses are accompanied by the rapid activation and growth of FRCs, leading to an expanded but similarly organized network of T-zone FRCs that maintains its vital function for lymphocyte trafficking and survival. In addition, new FRC-rich environments were observed in the expanded medullary cords. FRCs are activated within hours after the onset of inflammation in the periphery. Surprisingly, FRC expansion depends mainly on trapping of naïve lymphocytes that is induced by both migratory and resident dendritic cells. Inflammatory signals are not required as homeostatic T-cell proliferation was sufficient to trigger FRC expansion. Activated lymphocytes are also dispensable for this process, but can enhance the later growth phase. Thus, this study documents the surprising plasticity as well as the complex regulation of FRC networks allowing the rapid LN hyperplasia that is critical for mounting efficient adaptive immunity.
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http://dx.doi.org/10.1073/pnas.1312585111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3890876PMC
January 2014

Notch signaling regulates follicular helper T cell differentiation.

J Immunol 2013 Sep 5;191(5):2344-50. Epub 2013 Aug 5.

Department of Biochemistry, University of Lausanne, CH-1066 Epalinges, Switzerland.

Follicular helper T (TFH) cells are specialized in providing help for B cell differentiation and Ab secretion. Several positive and negative regulators of TFH cell differentiation have been described but their control is not fully understood. In this study, we show that Notch signaling in T cells is a major player in the development and function of TFH cells. T cell-specific gene ablation of Notch1 and Notch2 impaired differentiation of TFH cells in draining lymph nodes of mice immunized with T-dependent Ags or infected with parasites. Impaired TFH cell differentiation correlated with deficient germinal center development and the absence of high-affinity Abs. The impact of loss of Notch on TFH cell differentiation was largely independent of its effect on IL-4. These results show a previously unknown role for Notch in the regulation of TFH cell differentiation and function with implications for the control of this T cell population.
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http://dx.doi.org/10.4049/jimmunol.1300643DOI Listing
September 2013

Regulation of innate and adaptive immunity by Notch.

Nat Rev Immunol 2013 Jun 13;13(6):427-37. Epub 2013 May 13.

Ecole Polytechnique Fédérale de Lausanne, School of Life Sciences, Swiss Institute for Experimental Cancer Research, Lausanne, Vaud 1015, Switzerland.

Coordinated function of the innate and adaptive arms of the immune system in vertebrates is essential to promote protective immunity and to avoid immunopathology. The Notch signalling pathway, which was originally identified as a pleiotropic mediator of cell fate in invertebrates, has recently emerged as an important regulator of immune cell development and function. Notch was initially shown to be a key determinant of cell-lineage commitment in developing lymphocytes, but it is now known to control the homeostasis of several innate cell populations. Moreover, the roles of Notch in adaptive immunity have expanded to include the regulation of T cell differentiation and function. The aim of this Review is to summarize the current status of immune regulation by Notch. A better understanding of Notch function in both innate and adaptive immunity will hopefully provide multiple avenues for therapeutic intervention in disease.
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http://dx.doi.org/10.1038/nri3445DOI Listing
June 2013

Arginase activity - a marker of disease status in patients with visceral leishmaniasis in ethiopia.

PLoS Negl Trop Dis 2013 28;7(3):e2134. Epub 2013 Mar 28.

Department of Microbiology, Immunology and Parasitology, Addis Ababa University, Addis Ababa, Ethiopia.

The underlying mechanisms resulting in the profound immune suppression characteristic of human visceral leishmaniasis (VL) are not fully understood. Here, we tested the hypothesis that arginase, an enzyme associated with immunosuppression, is higher in patients with VL and contributes to impaired T cell responses. We recruited patients with VL before and after treatment and healthy controls and measured the arginase metabolism in the blood of these individuals. Our results show that arginase activity is significantly higher in the blood of patients with active VL as compared to controls. These high levels of arginase decline considerably once the patients are successfully treated. We identified the phenotype of arginase-expressing cells among PBMCs as neutrophils and show that their frequency was increased in PBMCs of patients before treatment; this coincides with reduced levels of L-arginine in the plasma and decreased expression levels of CD3ζ in T cells.
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http://dx.doi.org/10.1371/journal.pntd.0002134DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3610885PMC
August 2013