Leishmania lipophosphoglycan (LPG) activates NK cells through toll-like receptor-2

Differential structure and immunomodulatory functions of lipophosphoglycan between Leishmania spp

Leishmaniasis is a collective term for several tropical, neglected diseases caused by protozoans of the species Leishmania, 20 of which causing disease in humans ranging from localised self-healing lesions to chronic manifestations which affect the skin or inner organs. Although millions of infections are accounted for annually, treatment options are scarce and limited to medication associated with heavy side-effects and increasing antibiotic resistance. Case studies point towards immunotherapy as effective alternative treatment relying on immunomodulatory properties of e.g., the Bacillus Calmette-Guérin vaccine. Leishmania parasites are also known to modulate the immune system, yet the underlying macromolecules and surface molecules remain widely under characterised. With this short review, we aim to provide a complete summary of the existing literature describing one of the most expressed surface molecule on Leishmania spp, lipophosphoglycan (LPG), which shows great variability between different lifecycle stages and different Leishmania spp. Complete characterisation of LPG may aid to improve treatment and aid the development of vaccination strategies, and open new avenues to exploit the immunomodulatory properties of LPG in unrelated conditions.

TLR2/4 are novel activating receptors for SARS-CoV-2 spike protein on NK cells

Background

In early infected or severe coronavirus disease 2019 (COVID-19) patients, circulating NK cells are consistently reduced, despite being highly activated or exhausted. The aim of this paper was to establish whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (SP) may directly trigger NK cells and through which receptor(s).

Methods

SP-stimulated human NK cells have been evaluated for the expression of activation markers, cytokine release, and cytotoxic activity, as well as for gene expression profiles and NF-kB phosphorylation, and they have been silenced with specific small interfering RNAs.

Results

SPs from the Wuhan strain and other variants of concern (VOCs) directly bind and stimulate purified NK cells by increasing activation marker expression, cytokine release, and cytolytic activity, prevalently in the CD56brightNK cell subset. VOC-SPs differ in their ability to activate NK cells, G614, and Delta-Plus strains providing the strongest activity in the majority of donors. While VOC-SPs do not trigger ACE2, which is not expressed on NK cells, or other activating receptors, they directly and variably bind to both Toll-like receptor 2 (TLR2) and TLR4. Moreover, SP-driven NK cell functions are inhibited upon masking such receptors or silencing the relative genes. Lastly, VOC-SPs upregulate CD56dimNK cell functions in COVID-19 recovered, but not in non-infected, individuals.

Conclusions

TLR2 and TLR4 are novel activating receptors for SP in NK cells, suggesting a new role of these cells in orchestrating the pathophysiology of SARS-CoV-2 infection. The pathogenic relevance of this finding is highlighted by the fact that free SP providing NK cell activation is frequently detected in a SARS-CoV-2 inflamed environment and in plasma of infected and long-COVID-19 subjects.

Molecular regulation of NLRP3 inflammasome activation during parasitic infection

Parasitic diseases are a serious global health concern, causing many common and severe infections, including Chagas disease, leishmaniasis, and schistosomiasis. The NLRP3 inflammasome belongs to the NLR (nucleotide-binding domain leucine-rich-repeat-containing proteins) family, which are cytosolic proteins playing key roles in the detection of pathogens. NLRP3 inflammasomes are activated in immune responses to Plasmodium, Leishmania, Toxoplasma gondii, Entamoeba histolytica, Trypanosoma cruzi, and other parasites. The role of NLRP3 is not fully understood, but it is a crucial component of the innate immune response to parasitic infections and its functions as a sensor triggering the inflammatory response to the invasive parasites. However, while this response can limit the parasites' growth, it can also result in potentially catastrophic host pathology. This makes it essential to understand how NLRP3 interacts with parasites to initiate the inflammatory response. Plasmodium hemozoin, Leishmania glycoconjugate lipophosphoglycan (LPG) and E. histolytica Gal/GalNAc lectin can stimulate NLRP3 activation, while the dense granule protein 9 (GRA9) of T. gondii has been shown to suppress it. Several other parasitic products also have diverse effects on NLRP3 activation. Understanding the mechanism of NLRP3 interaction with these products will help to develop advanced therapeutic approaches to treat parasitic diseases. This review summarizes current knowledge of the NLRP3 inflammasome's action on the immune response to parasitic infections and aims to determine the mechanisms through which parasitic molecules either activate or inhibit its action.

Th17 Cell and Inflammatory Infiltrate Interactions in Cutaneous Leishmaniasis: Unraveling Immunopathogenic Mechanisms

The inflammatory response during cutaneous leishmaniasis (CL) involves immune and non-immune cell cooperation to contain and eliminate Leishmania parasites. The orchestration of these responses is coordinated primarily by CD4+ T cells; however, the disease outcome depends on the Th cell predominant phenotype. Although Th1 and Th2 phenotypes are the most addressed as steers for the resolution or perpetuation of the disease, Th17 cell activities, especially IL-17 release, are recognized to be vital during CL development. Th17 cells perform vital functions during both acute and chronic phases of CL. Overall, Th17 cells induce the migration of phagocytes (neutrophils, macrophages) to the infection site and CD8+ T cells and NK cell activation. They also provoke granzyme and perforin secretion from CD8+ T cells, macrophage differentiation towards an M2 phenotype, and expansion of B and Treg cells. Likewise, immune cells from the inflammatory infiltrate have modulatory activities over Th17 cells involving their differentiation from naive CD4+ T cells and further expansion by generating a microenvironment rich in optimal cytokines such as IL-1β, TGF-β, IL-6, and IL-21. Th17 cell activities and synergies are crucial for the resistance of the infection during the early and acute stages; however, if unchecked, Th17 cells might lead to a chronic stage. This review discusses the synergies between Th17 cells and the inflammatory infiltrate and how these interactions might destine the course of CL.

Natural Killer Cells and Cytotoxic T Cells: Complementary Partners against Microorganisms and Cancer

Natural killer (NK) cells and cytotoxic T (CD8+) cells are two of the most important types of immune cells in our body, protecting it from deadly invaders. While the NK cell is part of the innate immune system, the CD8+ cell is one of the major components of adaptive immunity. Still, these two very different types of cells share the most important function of destroying pathogen-infected and tumorous cells by releasing cytotoxic granules that promote proteolytic cleavage of harmful cells, leading to apoptosis. In this review, we look not only at NK and CD8+ T cells but also pay particular attention to their different subpopulations, the immune defenders that include the CD56+CD16dim, CD56dimCD16+, CD57+, and CD57+CD16+ NK cells, the NKT, CD57+CD8+, and KIR+CD8+ T cells, and ILCs. We examine all these cells in relation to their role in the protection of the body against different microorganisms and cancer, with an emphasis on their mechanisms and their clinical importance. Overall, close collaboration between NK cells and CD8+ T cells may play an important role in immune function and disease pathogenesis. The knowledge of how these immune cells interact in defending the body against pathogens and cancers may help us find ways to optimize their defensive and healing capabilities with methods that can be clinically applied.

Leishmania surface molecule lipophosphoglycan-TLR2 interaction moderates TPL2-mediated TLR2 signalling for parasite survival

Leishmania donovani, a protozoan parasite, resides and replicates in macrophages and inflicts the potentially fatal disease visceral leishmaniasis (VL). The parasite-expressed surface lipophosphoglycan (LPG) was implicated in binding TLR2 on NK cells, but the modus operandi of its disease-promoting influence remained unknown. As TPL2, a member of the MAPK module in mammalian macrophages, was implicated in the anti-inflammatory immune response and promoting pathogen survival, we investigated the possibility of TPL2-directed LPG-TLR2 signalling in Leishmania infection. We observed that TLR2 or TPL2 blockade differentially influenced the TLR2 ligand proteoglycan (PGN)-induced p38MAPK and ERK-1/2 activation. TLR2 blockade abrogated the PGN-induced TPL2 activation. L. donovani infection impaired the Akt activation whereas, upon TPL2 inhibition, the infection fails to control Akt phosphorylation. In L. donovani-infected macrophages, TLR2 blocking negatively affected p38, Akt and TPL2 phosphorylation while ERK1/2 phosphorylation increased relative to the infection alone. TPL2 blockade reduced TGF-β, but increased TNF-α expression and diminished amastigote count in macrophages. While exploring stimulation patterns of TLR2 ligands, LPG, unlike PGN, selectively increased TLR2 expression in macrophages. LPG blockade increased p38MAPK and AKT, but slightly affected ERK-1/2 and significantly reduced TPL2 phosphorylation from L. donovani-infected macrophages. Molecular docking and molecular dynamics analysis drew a parallel between LPG's glycan chain lengths with the frequency of interaction with TLR2 which might impact TLR2 signalling. Therefore, the parasite regulates the TLR2 signalling via TPL2 when elicited by LPG-TLR2 interaction for pathogenesis.

MicroRNAs regulating macrophages infected with Leishmania L. (V.) Braziliensis isolated from different clinical forms of American tegumentary leishmaniasis

Background

Leishmaniasis is an infectious disease caused by protozoa of the genus Leishmania. There are still no vaccines, and therapeutic options are limited, indicating the constant need to understand the fine mechanisms of its pathophysiology. An approach that has been explored in leishmaniasis is the participation of microRNAs (miRNAs), a class of small non-coding RNAs that act, in most cases, to repress gene expression. miRNAs play a role in the complex and plastic interaction between the host and pathogens, either as part of the host's immune response to neutralize infection or as a molecular strategy employed by the pathogen to modulate host pathways to its own benefit.

Methods

Monocyte-derived macrophages from healthy subjects were infected with isolates of three clinical forms of L. braziliensis: cutaneous (CL), mucosal (ML), and disseminated (DL) leishmaniasis. We compared the expression of miRNAs that take part in the TLR/NFkB pathways. Correlations with parasite load as well as immune parameters were analyzed.

Results

miRNAs -103a-3p, -21-3p, 125a-3p -155-5p, -146a-5p, -132- 5p, and -147a were differentially expressed in the metastatic ML and DL forms, and there was a direct correlation between miRNAs -103a-3p, -21-3p, -155-5p, -146a-5p, -132-5p, and -9-3p and parasite load with ML and DL isolates. We also found a correlation between the expression of miR-21-3p and miR-146a-5p with the antiapoptotic gene BCL2 and the increase of viable cells, whereas miR-147a was indirectly correlated with CXCL-9 levels.

Conclusion

The expression of miRNAs is strongly correlated with the parasite load and the inflammatory response, suggesting the participation of these molecules in the pathogenesis of the different clinical forms of L. braziliensis.

Development of a multi-epitope vaccine candidate for leishmanial parasites applying immunoinformatics and in vitro approaches

Leishmaniasis is a neglected tropical disease, and its severity necessitates the development of a potent and efficient vaccine for the disease; however, no human vaccine has yet been approved for clinical use. This study aims to design and evaluate a multi-epitope vaccine against the leishmanial parasite by utilizing helper T-lymphocyte (HTL), cytotoxic T-lymphocyte (CTL), and linear B-lymphocyte (LBL) epitopes from membrane-bound acid phosphatase of Leishmania donovani (LdMAcP). The designed multi-epitope vaccine (LdMAPV) was highly antigenic, non-allergenic, and non-toxic, with suitable physicochemical properties. The three-dimensional structure of LdMAPV was modeled and validated, succeeded by molecular docking and molecular dynamics simulation (MDS) studies that confirmed the high binding affinity and stable interactions between human toll-like receptors and LdMAPV. In silico disulfide engineering provided improved stability to LdMAPV, whereas immune simulation displayed the induction of both immune responses, i.e., antibody and cell-mediated immune responses, with a rise in cytokines. Furthermore, LdMAPV sequence was codon optimized and cloned into the pET-28a vector, followed by its expression in a bacterial host. The recombinant protein was purified using affinity chromatography and subjected to determine its effect on cytotoxicity, cytokines, and nitric oxide generation by mammalian macrophages. Altogether, this report provides a multi-epitope vaccine candidate from a leishmanial protein participating in parasitic virulence that has shown its potency to be a promising vaccine candidate against leishmanial parasites.

Leishmania major-derived lipophosphoglycan influences the host's early immune response by inducing platelet activation and DKK1 production via TLR1/2

Background

Platelets are rapidly deployed to infection sites and respond to pathogenic molecules via pattern recognition receptors (TLR, NLRP). Dickkopf1 (DKK1) is a quintessential Wnt antagonist produced by a variety of cell types including platelets, endothelial cells, and is known to modulate pro-inflammatory responses in infectious diseases and cancer. Moreover, DKK1 is critical for forming leukocyte-platelet aggregates and induction of type 2 cell-mediated immune responses. Our previous publication showed activated platelets release DKK1 following Leishmania major recognition.

Results

Here we probed the role of the key surface virulence glycoconjugate lipophosphoglycan (LPG), on DKK1 production using null mutants deficient in LPG synthesis (Δlpg1- and Δlpg2-). Leishmania-induced DKK1 production was reduced to control levels in the absence of LPG in both mutants and was restored upon re-expression of the cognate LPG1 or LPG2 genes. Furthermore, the formation of leukocyte-platelet aggregates was dependent on LPG. LPG mediated platelet activation and DKK1 production occurs through TLR1/2.

Conclusion

Thus, LPG is a key virulence factor that induces DKK1 production from activated platelets, and the circulating DKK1 promotes Th2 cell polarization. This suggests that LPG-activated platelets can drive innate and adaptive immune responses to Leishmania infection.

Leishmania braziliensis exosomes activate human macrophages to produce proinflammatory mediators

Exosomes, organelles measuring 30-200nm, are secreted by various cell types. Leishmania exosomes consist of many proteins, including heat shock proteins, annexins, Glycoprotein 63, proteins exerting signaling activity and those containing mRNA and miRNA. Studies have demonstrated that Leishmania donovani exosomes downregulate IFN-γ and inhibit the expression of microbicidal molecules, such as TNF and nitric oxide, thus creating a microenvironment favoring parasite proliferation. Despite lacking immunological memory, data in the literature suggest that, following initial stimulation, mononuclear phagocytes may become "trained" to respond more effectively to subsequent stimuli. Here we characterized the effects of macrophage sensitization using L. braziliensis exosomes prior to infection by the same pathogen. Human macrophages were stimulated with L. braziliensis exosomes and then infected with L. braziliensis. Higher levels of IL-1β and IL-6 were detected in cultures sensitized prior to infection compared to unstimulated infected cells. Moreover, stimulation with L. braziliensis exosomes induced macrophage production of IL-1β, IL-6, IL-10 and TNF. Inhibition of exosome secretion by L. braziliensis prior to macrophage infection reduced cytokine production and produced lower infection rates than untreated infected cells. Exosome stimulation also induced the consumption/regulation of NLRP3 inflammasome components in macrophages, while the blockade of NLRP3 resulted in lower levels of IL-6 and IL-1β. Our results suggest that L. braziliensis exosomes stimulate macrophages, leading to an exacerbated inflammatory state that may be NLRP3-dependent.

Toll-like receptor 2 selectively modulates Ras isoforms expression in Leishmania major infection

Leishmania infection of macrophages results in altered Ras isoforms expression and Toll-like receptor-2 (TLR2) expression and functions. Therefore, we examined whether TLR2 would selectively alter Ras isoforms' expression in macrophages. We observed that TLR2 ligands- Pam3CSK4, peptidoglycan (PGN), and FSL- selectively modulated the expression of Ras isoforms in BALB/c-derived elicited macrophages. Lentivirally-expressed TLR1-shRNA significantly reversed this Ras isoforms expression profile. TLR2-deficient L. major-infected macrophages and the lymph node cells from the L. major-infected mice showed similarly reversed Ras isoforms expression. Transfection of the macrophages with the siRNAs for the adaptors- Myeloid Differentiation factor 88 (MyD88) and Toll-Interleukin-1 Receptor (TIR) domain-containing adaptor protein (TIRAP)- or Interleukin-1 Receptor-Associated Kinases (IRAKs)- IRAK1 and IRAK4- significantly inhibited the L. major-induced down-regulation of K-Ras, and up-regulation of N-Ras and H-Ras, expression. The TLR1/TLR2-ligand Pam3CSK4 increased IL-10 and TGF-β expression in macrophages. Pam3CSK4 upregulated N-Ras and H-Ras, but down-regulated K-Ras, expression in C57BL/6 wild-type, but not in IL-10-deficient, macrophages. IL-10 or TGF-β signaling inhibition selectively regulated Ras isoforms expression. These observations indicate the specificity of the TLR2 regulation of Ras isoforms and their selective modulation by MyD88, TIRAP, and IRAKs, but not IL-10 or TGF-β, signaling.

The Complexity of Interferon Signaling in Host Defense against Protozoan Parasite Infection

Protozoan parasites, such as Plasmodium, Leishmania, Toxoplasma, Cryptosporidium, and Trypanosoma, are causative agents of health-threatening diseases in both humans and animals, leading to significant health risks and socioeconomic losses globally. The development of effective therapeutic and prevention strategies for protozoan-caused diseases requires a full understanding of the pathogenesis and protective events occurring in infected hosts. Interferons (IFNs) are a family of cytokines with diverse biological effects in host antimicrobial defense and disease pathogenesis, including protozoan parasite infection. Type II IFN (IFN-γ) has been widely recognized as the essential defense cytokine in intracellular protozoan parasite infection, whereas recent studies also revealed the production and distinct function of type I and III IFNs in host defense against these parasites. Decoding the complex network of the IFN family in host-parasite interaction is critical for exploring potential new therapeutic strategies against intracellular protozoan parasite infection. Here, we review the complex effects of IFNs on the host defense against intracellular protozoan parasites and the crosstalk between distinct types of IFN signaling during infections.

Unraveling the role of natural killer cells in leishmaniasis

NK cells are known as frontline responders that are efficient in combating several maladies as well as leishmaniasis caused by Leishmania spp. As such they are being investigated to be used for adoptive transfer therapy and vaccine. In spite of the lack of antigen-specific receptors at their surface, NK cells can selectively recognize pathogens, accomplished by the activation of the receptors on the NK cell surface and also as the result of their effector functions. Activation of NK cells can occur through interaction between TLR-2 expressed on NK cells and. LPG of Leishmania parasites. In addition, NK cell activation can occur by cytokines (e.g., IFN-γ and IL-12) that also lead to producing cytokines and chemokines and lysis of target cells. This review summarizes several evidences that support NK cells activation for controlling leishmaniasis and the potentially lucrative roles of NK cells during leishmaniasis. Furthermore, we discuss strategies of Leishmania parasites in inhibiting NK cell functions. Leishmania LPG can utilizes TLR2 to evade host-immune responses. Also, Leishmania GP63 can directly binds to NK cells and modulates NK cell phenotype. Finally, this review analyzes the potentialities to harness NK cells effectiveness in therapy regimens and vaccinations.

Macrophage Mitochondrial Biogenesis and Metabolic Reprogramming Induced by Leishmania donovani Require Lipophosphoglycan and Type I Interferon Signaling

Pathogen-specific rewiring of host cell metabolism creates the metabolically adapted microenvironment required for pathogen replication. Here, we investigated the mechanisms governing the modulation of macrophage mitochondrial properties by the vacuolar pathogen Leishmania. We report that induction of oxidative phosphorylation and mitochondrial biogenesis by Leishmania donovani requires the virulence glycolipid lipophosphoglycan, which stimulates the expression of key transcriptional regulators and structural genes associated with the electron transport chain. Leishmania-induced mitochondriogenesis also requires a lipophosphoglycan-independent pathway involving type I interferon (IFN) receptor signaling. The observation that pharmacological induction of mitochondrial biogenesis enables an avirulent lipophosphoglycan-defective L. donovani mutant to survive in macrophages supports the notion that mitochondrial biogenesis contributes to the creation of a metabolically adapted environment propitious to the colonization of host cells by the parasite. This study provides novel insight into the complex mechanism by which Leishmania metacyclic promastigotes alter host cell mitochondrial biogenesis and metabolism during the colonization process. IMPORTANCE To colonize host phagocytes, Leishmania metacyclic promastigotes subvert host defense mechanisms and create a specialized intracellular niche adapted to their replication. This is accomplished through the action of virulence factors, including the surface coat glycoconjugate lipophosphoglycan. In addition, Leishmania induces proliferation of host cell mitochondria as well as metabolic reprogramming of macrophages. These metabolic alterations are crucial to the colonization process of macrophages, as they may provide metabolites required for parasite growth. In this study, we describe a new key role for lipophosphoglycan in the stimulation of oxidative phosphorylation and mitochondrial biogenesis. We also demonstrate that host cell pattern recognition receptors Toll-like receptor 4 (TLR4) and endosomal TLRs mediate these Leishmania-induced alterations of host cell mitochondrial biology, which also require type I IFN signaling. These findings provide new insight into how Leishmania creates a metabolically adapted environment favorable to their replication.

Leishmania kinetoplast DNA contributes to parasite burden in infected macrophages: Critical role of the cGAS-STING-TBK1 signaling pathway in macrophage parasitemia

Leishmania parasites harbor a unique network of circular DNA known as kinetoplast DNA (kDNA). The role of kDNA in leishmania infections is poorly understood. Herein, we show that kDNA delivery to the cytosol of Leishmania major infected THP-1 macrophages provoked increased parasite loads when compared to untreated cells, hinting at the involvement of cytosolic DNA sensors in facilitating parasite evasion from the immune system. Parasite proliferation was significantly hindered in cGAS- STING- and TBK-1 knockout THP-1 macrophages when compared to wild type cells. Nanostring nCounter gene expression analysis on L. major infected wild type versus knockout cells revealed that some of the most upregulated genes including, Granulysin (GNLY), Chitotriosidase-1 (CHIT1), Sialomucin core protein 24 (CD164), SLAM Family Member 7 (SLAMF7), insulin-like growth factor receptor 2 (IGF2R) and apolipoprotein E (APOE) were identical in infected cGAS and TBK1 knockout cells, implying their involvement in parasite control. Amlexanox treatment (a TBK1 inhibitor) of L. major infected wild type cells inhibited both the percentage and the parasite load of infected THP-1 cells and delayed footpad swelling in parasite infected mice. Collectively, these results suggest that leishmania parasites might hijack the cGAS-STING-TBK1 signaling pathway to their own advantage and the TBK1 inhibitor amlexanox could be of interest as a candidate drug in treatment of cutaneous leishmaniasis.

Single nucleotide polymorphisms in genes involved in immune responses and outcome of tegumentary leishmaniasis

Leishmaniases are neglected tropical diseases with a broad clinical spectrum. Tegumentary leishmaniasis (TL) is a disease caused by different Leishmania species, transmitted by phlebotomine sand flies and distributed worldwide. TL can present a cutaneous (CL) or mucocutaneous (MCL) clinical form depending on factors inherent to the parasite, the host and the vector. Polymorphisms in the immune response genes are host genetic factors that influence the pathogenesis or control of leishmaniasis. Single nucleotide polymorphisms (SNPs) in immune genes have been evaluated in several countries where leishmaniasis is endemic. In this review, we report studies on SNPs in several immune genes that might be associated with susceptibility or resistance to TL. We summarize studies from around the world and in Brazil, highlight the difficulties of these studies and future analyses needed to enhance our knowledge regarding host genetic factors in TL. Understanding the genetic characteristics of the host that facilitate resistance or susceptibility to leishmaniasis can contribute to the development of immunotherapy schedules for this disease. The current treatment methods are toxic, and no human vaccine is available.

Natural killer cell exhaustion in SARS-CoV-2 infection

At the end of 2019, an outbreak of a severe respiratory disease occurred in Wuhan China, and an increase in cases of unknown pneumonia was alerted. In January 2020, a new coronavirus named SARS-CoV-2 was identified as the cause. The virus spreads primarily through the respiratory tract, and lymphopenia and cytokine storms have been observed in severely ill patients. This suggests the existence of an immune dysregulation as an accompanying event during a serious illness caused by this virus. Natural killer (NK) cells are innate immune responders, critical for virus shedding and immunomodulation. Despite its importance in viral infections, the contribution of NK cells in the fight against SARS-CoV-2 has yet to be deciphered. Different studies in patients with COVID-19 suggest a significant reduction in the number and function of NK cells due to their exhaustion. In this review, we summarize the current understanding of how NK cells respond to SARS-CoV-2 infection.

The Pathogenicity and Virulence of Leishmania - interplay of virulence factors with host defenses

Leishmaniasis is a group of disease caused by the intracellular protozoan parasite of the genus Leishmania. Infection by different species of Leishmania results in various host immune responses, which usually lead to parasite clearance and may also contribute to pathogenesis and, hence, increasing the complexity of the disease. Interestingly, the parasite tends to reside within the unfriendly environment of the macrophages and has evolved various survival strategies to evade or modulate host immune defense. This can be attributed to the array of virulence factors of the vicious parasite, which target important host functioning and machineries. This review encompasses a holistic overview of leishmanial virulence factors, their role in assisting parasite-mediated evasion of host defense weaponries, and modulating epigenetic landscapes of host immune regulatory genes. Furthermore, the review also discusses the diagnostic potential of various leishmanial virulence factors and the advent of immunomodulators as futuristic antileishmanial drug therapy.

Leishmania infantum Defective in Lipophosphoglycan Biosynthesis Interferes With Activation of Human Neutrophils

Visceral leishmaniasis (VL) is often associated with hematologic manifestations that may interfere with neutrophil response. Lipophosphoglycan (LPG) is a major molecule on the surface of Leishmania promastigotes, which has been associated with several aspects of the parasite–vector–host interplay. Here, we investigated how LPG from Leishmania (L.) infantum, the principal etiological agent of VL in the New World, influences the initial establishment of infection during interaction with human neutrophils in an experimental setting in vitro. Human neutrophils obtained from peripheral blood samples were infected with either the wild-type L. infantum (WT) strain or LPG-deficient mutant (∆lpg1). In this setting, ∆lpg1 parasites displayed reduced viability compared to WT L. infantum; such finding was reverted in the complemented ∆lpg1+LPG1 parasites at 3- and 6-h post-infection. Confocal microscopy experiments indicated that this decreased survival was related to enhanced lysosomal fusion. In fact, LPG-deficient L. infantum parasites more frequently died inside neutrophil acidic compartments, a phenomenon that was reverted when host cells were treated with Wortmannin. We also observed an increase in the secretion of the neutrophil collagenase matrix metalloproteinase-8 (MMP-8) by cells infected with ∆lpg1 L. infantum compared to those that were infected with WT parasites. Furthermore, collagen I matrix degradation was found to be significantly increased in ∆lpg1 parasite-infected cells but not in WT-infected controls. Flow cytometry analysis revealed a substantial boost in production of reactive oxygen species (ROS) during infection with either WT or ∆lpg1 L. infantum. In addition, killing of ∆lpg1 parasites was shown to be more dependent on the ROS production than that of WT L. infantum. Notably, inhibition of the oxidative stress with Apocynin potentially fueled ∆lpg1 L. infantum fitness as it increased the intracellular parasite viability. Thus, our observations demonstrate that LPG may be a critical molecule fostering parasite survival in human neutrophils through a mechanism that involves cellular activation and generation of free radicals.

Insight Into the Long Noncoding RNA and mRNA Coexpression Profile in the Human Blood Transcriptome Upon Leishmania infantum Infection

Visceral leishmaniasis (VL) is a vector-borne infectious disease that can be potentially fatal if left untreated. In Brazil, it is caused by Leishmania infantum parasites. Blood transcriptomics allows us to assess the molecular mechanisms involved in the immunopathological processes of several clinical conditions, namely, parasitic diseases. Here, we performed mRNA sequencing of peripheral blood from patients with visceral leishmaniasis during the active phase of the disease and six months after successful treatment, when the patients were considered clinically cured. To strengthen the study, the RNA-seq data analysis included two other non-diseased groups composed of healthy uninfected volunteers and asymptomatic individuals. We identified thousands of differentially expressed genes between VL patients and non-diseased groups. Overall, pathway analysis corroborated the importance of signaling involving interferons, chemokines, Toll-like receptors and the neutrophil response. Cellular deconvolution of gene expression profiles was able to discriminate cellular subtypes, highlighting the contribution of plasma cells and NK cells in the course of the disease. Beyond the biological processes involved in the immunopathology of VL revealed by the expression of protein coding genes (PCGs), we observed a significant participation of long noncoding RNAs (lncRNAs) in our blood transcriptome dataset. Genome-wide analysis of lncRNAs expression in VL has never been performed. lncRNAs have been considered key regulators of disease progression, mainly in cancers; however, their pattern regulation may also help to understand the complexity and heterogeneity of host immune responses elicited by L. infantum infections in humans. Among our findings, we identified lncRNAs such as IL21-AS1, MIR4435-2HG and LINC01501 and coexpressed lncRNA/mRNA pairs such as CA3-AS1/CA1, GASAL1/IFNG and LINC01127/IL1R1-IL1R2. Thus, for the first time, we present an integrated analysis of PCGs and lncRNAs by exploring the lncRNA–mRNA coexpression profile of VL to provide insights into the regulatory gene network involved in the development of this inflammatory and infectious disease.

Effect of hybridization on Lipophosphoglycan expression in Leishmania major

Leishmania major is the causative agent of cutaneous leishmaniasis (CL). It is one of the most studied Leishmania species not only during vector interaction, but also in the vertebrate host. Lipophosphoglycan (LPG) is the Leishmania multifunctional virulence factor during host-parasite interaction, whose polymorphisms are involved in the immunopathology of leishmaniasis. Although natural hybrids occur in nature, hybridization of L. major strains in the laboratory was successfully demonstrated. However, LPG expression in the hybrids remains unknown. LPGs from parental (Friedlin-Fn and Seidman-Sd) and hybrids (FnSd3, FnSd4A, FnSd4B and FnSd6F) were extracted, purified and their repeat units analyzed by immunoblotting and fluorophore-assisted carbohydrate electrophoresis (FACE). Parental strains have distinct profiles in LPG expression, and a mixed profile was observed for all hybrids. Variable levels of NO production by macrophages were detected after LPG exposure (parental and hybrids) and were strain specific. This article is protected by copyright. All rights reserved.

The c-MET receptor tyrosine kinase contributes to neutrophil-driven pathology in cutaneous leishmaniasis

Neutrophils are the first line of defence against invading pathogens. Although neutrophils are well-known professional killers, some pathogens including Leishmania (L.) parasites survive in neutrophils, using these cells to establish infection. Manipulation of neutrophil recruitment to the infection site is therefore of interest in this cutaneous disease. The c-MET tyrosine kinase receptor was shown to promote neutrophil migration to inflamed sites. Here, we investigated the importance of c-MET expression on neutrophils in their recruitment to the infection site and the role of c-Met expression in the pathology of leishmaniasis. Following infection with L. mexicana, mice with conditional deletion of c-MET in neutrophils controlled significantly better their lesion development and parasite burden compared to similarly infected wild type mice. Our data reveal a specific role for c-MET activation in Leishmania-induced neutrophil infiltration, a process correlating with their negative role in the pathology of the diseases. We further show that c-MET phosphorylation is observed in established cutaneous lesions. Exposure to L. mexicana upregulated c-Met expression predominantly in infected neutrophils and c-Met expression influenced ROS release by neutrophils. In addition, pharmacological inhibition of c-MET, administrated once the lesion is established, induced a significant decrease in lesion size associated with diminished infiltration of neutrophils. Both genetic ablation of c-MET in neutrophils and systemic inhibition of c-MET locally resulted in higher levels of CD4+T cells producing IFNγ, suggesting a crosstalk between neutrophils and these cells. Collectively, our data show that c-MET activation in neutrophils contributes to their recruitment following infection, and that L. mexicana induction of c-MET on neutrophils impacts the local pathology associated with this disease. Our results suggest a potential use for this inhibitor in the control of the cutaneous lesion during this parasitic infection.

Purinergic Enhancement of Anti-Leishmanial Effector Functions of Neutrophil Granulocytes

Although macrophages are considered for host cells for the multiplication of Leishmania, recent studies indicate the important role of neutrophil granulocytes as host cells for these intracellular parasites. Neutrophils have been shown to be massively and rapidly recruited to the site of Leishmania infection where they represent the first cells to encounter the parasites. Exposure to ATP and UTP have been shown to enhance anti-Leishmania activity of macrophages and intralesional injection of UTP led to strongly reduced parasite load in vivo. Since the in vivo anti-leishmanial effect of extracellular UTP correlated with enhanced neutrophil recruitment and enhanced ROS production at the site of Leishmania infection we hypothesized that exposure to extracellular nucleotides can directly enhance the killing of Leishmania by neutrophils. Since purinergic signaling is an essential mechanism of neutrophil activation the aim of the present study was to assess whether purinergic exposure results in the activation of anti-leishmanial neutrophil functions and, therefore, represent an essential component of enhanced anti-leishmanial defense in leishmaniasis. We could show that exposure to ATP and UTP led to activation and enhanced CD11b expression of primary human neutrophils in vitro. Leishmania-induced ROS production was strongly enhanced by extracellular ATP and UTP. Importantly, exposure to ATP and UTP resulted in enhanced killing of Leishmania donovani by neutrophils. In addition, ATP strongly enhanced the secretion of IL-8 and IL-1β by Leishmania-exposed neutrophils. Our results suggest that signaling via the P2 receptor and phosphorylation of Erk1/2, Akt and p38 are involved in the purinergic enhancement of anti-leishmanial functions of neutrophils.

Determinants of Innate Immunity in Visceral Leishmaniasis and Their Implication in Vaccine Development

Leishmaniasis is endemic to the tropical and subtropical regions of the world and is transmitted by the bite of an infected sand fly. The multifaceted interactions between Leishmania, the host innate immune cells, and the adaptive immunity determine the severity of pathogenesis and disease development. Leishmania parasites establish a chronic infection by subversion and attenuation of the microbicidal functions of phagocytic innate immune cells such as neutrophils, macrophages and dendritic cells (DCs). Other innate cells such as inflammatory monocytes, mast cells and NK cells, also contribute to resistance and/or susceptibility to Leishmania infection. In addition to the cytokine/chemokine signals from the innate immune cells, recent studies identified the subtle shifts in the metabolic pathways of the innate cells that activate distinct immune signal cascades. The nexus between metabolic pathways, epigenetic reprogramming and the immune signaling cascades that drive the divergent innate immune responses, remains to be fully understood in Leishmania pathogenesis. Further, development of safe and efficacious vaccines against Leishmaniasis requires a broader understanding of the early interactions between the parasites and innate immune cells. In this review we focus on the current understanding of the specific role of innate immune cells, the metabolomic and epigenetic reprogramming and immune regulation that occurs during visceral leishmaniasis, and the strategies used by the parasite to evade and modulate host immunity. We highlight how such pathways could be exploited in the development of safe and efficacious Leishmania vaccines.

Blockade of TLR2 and TLR4 Attenuates Inflammatory Response and Parasite Load in Cutaneous Leishmaniasis

Human cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is characterized by a pronounced inflammatory response associated with ulcer development. Monocytes/macrophages, the main cells harboring parasites, are largely responsible for parasite control. Toll-like receptor (TLR) signaling leads to the transcription of inflammatory mediators, such as IL-1β and TNF during innate immune response. TLR antagonists have been used in the treatment of inflammatory disease. The neutralization of these receptors may attenuate an exacerbated inflammatory response. We evaluated the ability of TLR2 and TLR4 antagonists to modulate host immune response in L. braziliensis-infected monocytes and cells from CL patient skin lesions. Following TLR2 and TLR4 neutralization, decreased numbers of infected cells and internalized parasites were detected in CL patient monocytes. In addition, reductions in oxidative burst, IL-1β, TNF and CXCL9 production were observed. TNF production by cells from CL lesions also decreased after TLR2 and TLR4 neutralization. The attenuation of host inflammatory response after neutralizing these receptors suggests the potential of TLR antagonists as immunomodulators in association with antimonial therapy in human cutaneous leishmaniasis.

Role of Toll-like receptors in natural killer cell function in acute lymphoblastic leukemia

Natural killer (NK) cells are specialized lymphocytes primarily involved in the response to infection and tumors. NK cells are characterized by the presence of specific surface molecules, as well as a wide repertoire of receptors that impart microenvironment-dependent effector functions. Among these receptors, Toll-like receptors (TLRs) can be activated to condition the NK response to either a cytotoxic or immunoregulatory phenotype. However, cellular function is frequently impaired during disorders such as cancer. In the last decade, it has become increasingly evident that the stimulation of NK cells is a requirement for their increased cytotoxic activity. TLR activation has been suggested as an alternative route for reestablishing the antitumor activity of NK cells. The present review summarizes the characteristics of NK cells, their receptors, the expression and function of NK cell TLRs, and their functional status in cancer, primarily acute lymphoblastic leukemia.

Vaccination against the Protozoan Parasite Histomonas meleagridis Primes the Activation of Toll-like Receptors in Turkeys and Chickens Determined by a Set of Newly Developed Multiplex RT-qPCRs

Histomonosis in turkeys and chickens is caused by the extracellular parasite Histomonas meleagridis, but the outcome of the disease varies depending on the host species. So far, studies on the immune response against histomonosis focus mainly on different traits of the adaptive immune system. Activation of toll like receptors (TLR) leads to the interplay between cells of innate and adaptive immunity with consequences on B and T cell clonal expansion. Therefore, the present investigation focused on the interaction of virulent and/or attenuated histomonads with the innate immune system of turkeys and chickens at 4, 10, 21 days post inoculation. The expression of TLRs (TLR1A, 1B, 2A, 2B, 3, 4, 5, 6(Tu), 7, 13(Tu) and 21(Ch)) and pro-inflammatory cytokines (IL1β and IL6) were analysed in caecum and spleen samples by RT-qPCR. Most frequent significant changes in expression levels of TLRs were observed in the caecum following infection with virulent parasites, an effect noticed to a lower degree in tissue samples from birds vaccinated with attenuated parasites. TLR1B, 2B and 4 showed a continuous up-regulation in the caecum of both species during infection or vaccination, followed by challenge with virulent parasites. Vaccinated birds of both species showed a significant earlier change in TLR expression following challenge than birds kept non-vaccinated but challenged. Expression of TLRs and pro-inflammatory cytokines were associated with severe inflammation of diseased birds in the local organ caecum. In the spleen, changes in TLRs and pro-inflammatory cytokines were less prominent and mainly observed in turkey samples. In conclusion, a detailed comparison of TLRs and pro-inflammatory cytokines of the innate immune system following inoculation with attenuated and/or virulent H. meleagridis of two avian host species provides an insight into regulative mechanisms of TLRs in the development of protection and limitation of the disease.

Trypanosoma brucei Lipophosphoglycan Induces the Formation of Neutrophil Extracellular Traps and Reactive Oxygen Species Burst via Toll-Like Receptor 2, Toll-Like Receptor 4, and c-Jun N-Terminal Kinase Activation

Trypanosoma brucei brucei is the causative agent of African animal trypanosomosis, which mainly parasitizes the blood of the host. Lipophosphoglycan (LPG), a polymer anchored to the surface of the parasites, activates the host immune response. In this study, we revealed that T. brucei LPG stimulated neutrophils to form neutrophil extracellular traps (NETs) and release the reactive oxygen species (ROS). We further analyzed the involvement of toll-like receptor 2 (TLR2) and toll-like receptor 4 (TLR4) and explored the activation of signaling pathway enzymes in response to LPG stimulation. During the stimulation of neutrophils by LPG, the blockade using anti-TLR2 and anti-TLR4 antibodies reduced the phosphorylation of c-Jun N-terminal kinase (JNK), the release of DNA from the NETs, and the burst of ROS. Moreover, the addition of JNK inhibitor and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor exhibited similar effects. Our data suggest that T. brucei LPG activates the phosphorylation of JNK through TLR2 and TLR4 recognition, which causes the formation of NETs and the burst of ROS.

Miltefosine enhances infectivity of a miltefosine-resistant Leishmania infantum strain by attenuating its innate immune recognition

Background

Miltefosine (MIL) is currently the only oral drug available to treat visceral leishmaniasis but its use as first-line monotherapy has been compromised by an increasing treatment failure. Despite the scarce number of resistant clinical isolates, MIL-resistance by mutations in a single aminophospholipid transporter gene can easily be selected in a laboratory environment. These mutations result in a reduced survival in the mammalian host, which can partially be restored by exposure to MIL, suggesting a kind of drug-dependency.

Methodology/Principal findings

To enable a combined study of the infection dynamics and underlying immunological events for differential in vivo survival, firefly luciferase (PpyRE9) / red fluorescent protein (DsRed) double-reporter strains were generated of MIL-resistant (MIL-R) and syngeneic MIL-sensitive (MIL-S) Leishmania infantum. Results in C57Bl/6 and BALB/c mice show that MIL-R parasites induce an increased innate immune response that is characterized by enhanced influx and infection of neutrophils, monocytes and dendritic cells in the liver and elevated serum IFN-γ levels, finally resulting in a less efficient establishment in liver macrophages. The elevated IFN-γ levels were shown to originate from an increased response of hepatic NK and NKT cells to the MIL-R parasites. In addition, we demonstrated that MIL could increase the in vivo fitness of MIL-R parasites by lowering NK and NKT cell activation, leading to a reduced IFN-γ production.

Conclusions/Significance

Differential induction of innate immune responses in the liver was found to underlie the attenuated phenotype of a MIL-R parasite and its peculiar feature of drug-dependency. The impact of MIL on hepatic NK and NKT activation and IFN-γ production following recognition of a MIL-R strain indicates that this mechanism may sustain infections with resistant parasites and contribute to treatment failure.

Visceral leishmaniasis is a neglected tropical disease that is fatal if left untreated. Miltefosine is currently the only oral drug available but is increasingly failing to cure patients, resulting in its discontinuation as first-line drug in some endemic areas. To understand these treatment failures, we investigated the complex interplay of the parasite with the host immune system in the presence and absence of miltefosine. Our data indicate that miltefosine-resistant Leishmania parasites become severely hampered in their in vivo infectivity, which could be attributed to the induction of a pronounced innate immune response. Interestingly, the infection deficit was partially restored in the presence of miltefosine. Our results further indicate that miltefosine can exacerbate infections with resistant parasites by reducing innate immune recognition. This study provides new insights into the complex interplay between parasite, drug and host and discloses an immune-related mechanism of treatment failure.

Innate immune response: ally or enemy in cutaneous leishmaniasis?

Cutaneous leishmaniasis (CL) is an infectious and neglected disease caused by parasites of the genus Leishmania, which produces a wide spectrum of cutaneous manifestations. CL research has shown that the innate immune activity of cells such as neutrophils, natural killers, macrophages, dendritic cells and the complement system are capable of controlling this infection. However, Leishmania can also modulate the immune activity of these cells to promote its own survival and proliferation at the intracellular level. This review discusses the role of the innate immune response in the control and spread of this infection.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

The Absence of HIF-1α Increases Susceptibility to Leishmania donovani Infection via Activation of BNIP3/mTOR/SREBP-1c Axis

Hypoxia-inducible factor-1 alpha (HIF-1α) is considered a global regulator of cellular metabolism and innate immune cell functions. Intracellular pathogens such as Leishmania have been reported to manipulate host cell metabolism. Herein, we demonstrate that myeloid cells from myeloid-restricted HIF-1α-deficient mice and individuals with loss-of-function HIF1A gene polymorphisms are more susceptible to L. donovani infection through increased lipogenesis. Absence of HIF-1α leads to a defect in BNIP3 expression, resulting in the activation of mTOR and nuclear translocation of SREBP-1c. We observed the induction of lipogenic gene transcripts, such as FASN, and lipid accumulation in infected HIF-1α^-/- macrophages. L. donovani-infected HIF-1α-deficient mice develop hypertriglyceridemia and lipid accumulation in splenic and hepatic myeloid cells. Most importantly, our data demonstrate that manipulating FASN or SREBP-1c using pharmacological inhibitors significantly reduced parasite burden. As such, genetic deficiency of HIF-1α is associated with increased lipid accumulation, which results in impaired host-protective anti-leishmanial functions of myeloid cells.

Development of Fish Parasite Vaccines in the OMICs Era: Progress and Opportunities

Globally, parasites are increasingly being recognized as catastrophic agents in both aquaculture sector and in the wild aquatic habitats leading to an estimated annual loss between 1.05 billion and 9.58 billion USD. The currently available therapeutic and control measures are accompanied by many limitations. Hence, vaccines are recommended as the "only green and effective solution" to address these concerns and protect fish from pathogens. However, vaccine development warrants a better understanding of host-parasite interaction and parasite biology. Currently, only one commercial parasite vaccine is available against the ectoparasite sea lice. Additionally, only a few trials have reported potential vaccine candidates against endoparasites. Transcriptome, genome, and proteomic data at present are available only for a limited number of aquatic parasites. Omics-based interventions can be significant in the identification of suitable vaccine candidates, finally leading to the development of multivalent vaccines for significant protection against parasitic infections in fish. The present review highlights the progress in the immunobiology of pathogenic parasites and the prospects of vaccine development. Finally, an approach for developing a multivalent vaccine for parasitic diseases is presented. Data sources to prepare this review included Pubmed, google scholar, official reports, and websites.

Understanding the immune responses involved in mediating protection or immunopathology during leishmaniasis

Leishmaniasis is a vector-borne Neglected Tropical Disease (NTD) transmitted by the sand fly and is a major public health problem worldwide. Infections caused by Leishmania clinically manifest as a wide range of diseases, such as cutaneous (CL), diffuse cutaneous (DCL), mucosal (MCL) and visceral leishmaniasis (VL). The host innate and adaptative immune responses play critical roles in the defense against leishmaniasis. However, Leishmania parasites also manipulate the host immune response for their survival and replication. In addition, other factors such as sand fly salivary proteins and microbiota also promote disease susceptibility and parasite spread by modulating local immune response. Thus, a complex interplay between parasite, sand fly and the host immunity governs disease severity and outcome. In this review, we discuss the host immune response during Leishmania infection and highlight the factors associated with resistance or susceptibility.

Neutrophils and Visceral Leishmaniasis: Impact on innate immune response and cross-talks with macrophages and dendritic cells

Neutrophils with their array of microbicidal activities are the first innate immune cells to guard against infection. They are also most crucial for the host's initial defense against Leishmania parasites which cause clinically diverse diseases ranging from self-healing cutaneous leishmaniasis (CL) to a more severe visceral form, visceral leishmaniasis (VL). Neutrophils are recruited in large numbers at the infection site after bite of sandfly, which is the vector for the disease. The initial interaction of neutrophils with the parasites may modulate the subsequent innate and adaptive immune responses and hence affect the disease outcome. The purpose of this review is to comprehensively appraise the role of neutrophils during the early stages of Leishmania infection with a focus on the visceral form of the disease. In the past decade, new insights regarding the role of neutrophils in VL have surfaced which have been extensively elaborated in the present review. In addition, since much of the information regarding neutrophil-Leishmania early interaction has accumulated through studies on mouse models of CL, these studies are also revisited. We begin by reviewing the factors which drive the recruitment of neutrophils at the site of injection by the sandfly. We then discuss the studies delineating the molecular mechanisms involved in the uptake of the Leishmania parasite by neutrophils and how the parasite subverts their microbicidal functions. In the end, the interaction of infected neutrophils with macrophages and dendritic cells is summarized.

Granzyme B Produced by Natural Killer Cells Enhances Inflammatory Response and Contributes to the Immunopathology of Cutaneous Leishmaniasis

BACKGROUND

Skin lesions from patients infected with Leishmania braziliensis has been associated with inflammation induced by cytotoxic CD8+ T cells. In addition, CD8+ T cell-mediated cytotoxicity has not been linked to parasite killing. Meanwhile, the cytotoxic role played by natural killer (NK) cells in cutaneous leishmaniasis (CL) remains poorly understood.

METHODS

In this study, we observed higher frequencies of NK cells in the peripheral blood of CL patients compared with healthy subjects, and that NK cells expressed more interferon-γ, tumor necrosis factor (TNF), granzyme B, and perforin than CD8+ T cells.

RESULTS

We also found that most of the cytotoxic activity in CL lesions was triggered by NK cells, and that the high levels of granzyme B produced in CL lesions was associated with larger lesion size. Furthermore, an in vitro blockade of granzyme B was observed to decrease TNF production.

CONCCLUSIONS

Our data, taken together, suggest an important role by NK cells in inducing inflammation in CL, thereby contributing to disease immunopathology.

Leishmania amazonensis Promastigotes or Extracellular Vesicles Modulate B-1 Cell Activation and Differentiation

B-1 cells are considered an innate-like B cell population that participates in effective innate and adaptive responses to pathogens. B-1 cells produce immunoglobulins, cytokines, chemokines, migrate to inflammatory sites, and differentiate into mononuclear phagocyte-like cells. Murine B-1 cells phagocytosed Leishmaniain vitro and in vivo and participate in immunity against Leishmania. Our group showed that B-1 cells or their extracellular vesicles (EVs) led to a resistance to experimental infection by L. amazonensis. However, the B-1 cells’ responses to Leishmania or EVs isolated from parasites are still poorly characterized. Studying the activation and differentiation of B-1 cells in vivo can contribute to a better understanding of how these cells participate in immunity to L. amazonensis. Thus, we evaluated the expression of myeloid (M-csfr, G-csfr, Spi-1) and lymphoid (EBF, E2A, IL-7R) lineage commitment factors, Toll-like receptors (TLRs), activation cell surface markers, nitric oxide (NO) and reactive oxygen species (ROS) production in murine peritoneal B-1 cells collected after 24 or 48 h post-infection with Leishmania (Leishmania) amazonensis promastigotes or EVs released by the parasites. Our results demonstrated that L. amazonensis infection did not stimulate the expression of CD40, CD80, CD86, F4/80, and MHC II in B-1 cells, but a significant decrease in the production of NO and ROS was observed. The infection induced a significantly higher arginase expression in B-1 cells, but the stimulation with EVs led to a decrease in this gene expression. TLR-2 and TLR-6 had significantly higher expression in B-1 cells from mice intraperitoneally stimulated with the parasite. The TLR-9 expression was higher in animals infected or stimulated for 48 h with EVs. Interestingly, in B-1 cells the stimulus with L. amazonensis led to a substantial increase in the expression of myeloid restricted transcription factors. Thus, our study suggests that the parasites or EVs differently modulated the activation and differentiation of B-1 cells.

Enhanced production of pro-inflammatory cytokines and chemokines in Ethiopian cutaneous leishmaniasis upon exposure to Leishmania aethiopica

The clinical course and outcome of cutaneous leishmaniasis (CL) vary due to the infecting Leishmania species and host genetic makeup that result in different immune responses against the parasites. The host immune response to Leishmania aethiopica (L.aethiopica), the causative agent of CL in Ethiopia, is poorly understood. To contribute to the understanding of the protective immune response in CL due to L.aethiopica, we characterized the cytokine response to L. aethiopica in patients with the localized form of CL (LCL) and age-and sex-matched apparently healthy controls. By applying a whole blood based in vitro culture we found enhanced release of TNF, IL-6, MCP-1 or CCL2, IP-10 or CXCL10, MIP-1β or CCL4 and IL-8 or CXCL8- but not of IL-10CL patients in response to L. aethiopica compared to the controls. No difference was observed between LCL cases and controls in the secretion of these cytokines and chemokines in whole blood cultures treated with the TLR-ligands LPS, MALP-2 or polyI: C. The observed increased secretion of the pro-inflammatory cytokines/chemokines reflects an enhanced response against the parasites by LCL patients as compared to healthy controls rather than a generally enhanced ability of blood leukocytes from LCL patients to respond to microbial constituents. Our findings suggest that the enhanced production of pro-inflammatory cytokines/chemokines is associated with localized cutaneous leishmaniasis caused by L.aethiopica.

NK cells and ILCs in tumor immunotherapy

Cells of the innate immunity play an important role in tumor immunotherapy. Thus, NK cells can control tumor growth and metastatic spread. Thanks to their strong cytolytic activity against tumors, different approaches have been developed for exploiting/harnessing their function in patients with leukemia or solid tumors. Pioneering trials were based on the adoptive transfer of autologous NK cell-enriched cell populations that were expanded in vitro and co-infused with IL-2. Although relevant results were obtained in patients with advanced melanoma, the effect was mostly limited to certain metastatic localizations, particularly to the lung. In addition, the severe IL-2-related toxicity and the preferential IL-2-induced expansion of Treg limited this type of approach. This limitation may be overcome by the use of IL-15, particularly of modified IL-15 molecules to improve its half-life and optimize the biological effects. Other approaches to harness NK cell function include stimulation via TLR, the use of bi- and tri-specific NK cell engagers (BiKE and TriKE) linking activating NK receptors (e.g. CD16) to tumor-associated antigens and even incorporating an IL-15 moiety (TriKE). As recently shown, in tumor patients, NK cells may also express inhibitory checkpoints, primarily PD-1. Accordingly, the therapeutic use of checkpoint inhibitors may unleash NK cells against PD-L1⁺ tumors. This effect may be predominant and crucial in tumors that have lost HLA cl-I expression, thus resulting "invisible" to T lymphocytes. Additional approaches in which NK cells may represent an important tool for cancer therapy, are to exploit the unique properties of the "adaptive" NK cells. These CD57⁺ NKG2C⁺ cells, despite their mature stage and a potent cytolytic activity, maintain a strong proliferating capacity. This property revealed to be crucial in hematopoietic stem cell transplantation (HSCT), particularly in the haplo-HSCT setting, to cure high-risk leukemias. T depleted haplo-HSCT (e.g. from one of the parents) allowed to save the life of thousands of patients lacking a HLA-compatible donor. In this setting, NK cells have been shown to play an essential role against leukemia cells and infections. Another major advance is represented by chimeric antigen receptor (CAR)-engineered NK cells. CAR-NK, different from CAR-T cells, may be obtained from allogeneic donors since they do not cause GvHD. Accordingly, they may represent "off-the-shelf" products to promptly treat tumor patients, with affordable costs. Different from NK cells, helper ILC (ILC1, ILC2 and ILC3), the innate counterpart of T helper cell subsets, remain rather ambiguous with respect to their anti-tumor activity. A possible exception is represented by a subset of ILC3: their frequency in peri-tumoral tissues in patients with NSCLC directly correlates with a better prognosis, possibly reflecting their ability to contribute to the organization of tertiary lymphoid structures, an important site of T cell-mediated anti-tumor responses. It is conceivable that innate immunity may significantly contribute to the major advances that immunotherapy has ensured and will continue to ensure to the cure of cancer.

Insight into the sequence-structure relationship of TLR cytoplasm's Toll/Interleukin-1 receptor domain towards understanding the conserved functionality of TLR 2 heterodimer in mammals

The signaling response of TLR2 to ligands has always been as a homodimer or in heterodimerization with TLR1/TLR6. The Toll/Interleukin-1 Receptor (TIR) domain of the TLR cytoplasmic region regulates the dimerization and interactions with adaptor molecules to build an active signaling complex. To understand the conservation of functionality of the TLR2-heterodimers between the distantly related species human(h) and mice(m), the pattern of TIR-TIR interaction in heterodimers has been studied through the sequence-structural point of view. Comparative analysis of primary sequence and structural pattern of TLRs(1/2/6) corroborates higher sequence homology between TLR1 and TLR6. Molecular docking analysis of TLR2-TLR1 and TLR2-TLR6 cytoplasmic dimers in both mouse and human have identified that for interaction the BB loop/near-BB loop residues of TLR2 are involved with the near-DD loop of TLR1 and DD loop residues of TLR6 within the TIR domains, which may cause to differential signaling. Molecular dynamics simulation of dimers for both human and mice species recognize stable interface between near-BB/BB loop region of TLR2 and discrete near-DD and DD loop region of TLR1 and TLR6 respectively. The observed dimerization pattern in both the species is further supported by Alanine scanning mutation study. However, Solvent Accessible Surface Area (SASA) of BB and DD loop regions of the cytoplasmic monomers and the heterodimers suggests that while TLR2 BB loop is actively associated as the dimer interface with its heterodimer partners in both the species, the DD loop acts as the active interfacing region in hTLR1 and mTLR6. Communicated by Ramaswamy H. Sarma.

Reconciling protective and pathogenic roles of the NLRP3 inflammasome in leishmaniasis

Leishmaniasis is a global health problem that affects more than 2 billion people worldwide. Recent advances in research have demonstrated critical roles for cytoplasmic sensors and inflammasomes during Leishmania spp. infection and pathogenesis. Specifically, several studies have focused on the role of nod-like receptor family, pyrin domain-containing protein 3 (NLRP3) inflammasome and inflammasome-associated cytokines IL-1β and IL-18 in leishmaniasis. Despite these studies, our understanding of the priming and activation events that lead to NLRP3 inflammasome activation during Leishmania spp. infection is limited. Furthermore, whether NLRP3 plays a protective or pathogenic role during Leishmania spp. infection is far from resolved, with some studies showing a protective role and others showing a pathogenic role. In this review, we performed a critical review of the literature to provide a current update on priming and activating signals required for NLRP3 inflammasome activation during Leishmania spp. infection. Finally, we provide a thorough review of the literature to reconcile differences in the observed protective vs pathogenic roles of the NLRP3 inflammasome during Leishmania spp. infection.

Review on the Role of Host Immune Response in Protection and Immunopathogenesis during Cutaneous Leishmaniasis Infection

Cutaneous leishmaniasis (CL) is a major public health problem worldwide and spreads to human via the bite of sand flies during blood meal. Following its inoculation, the promastigotes are immediately taken up by phagocytic cells and these leishmania-infected host cells produce proinflammatory cytokines that activate other immune cells and these infected host cells produce more cytokines and reactive nitrogen and oxygen species for efficient control of leishmania infection. Many experimental studies showed that resistance to infection with leishmania paraites is associated with the production of proinflammatory cytokines and activation of CD4⁺ Th1 response. On the other hand, vulnerability to this parasitic infection is correlated to production of T helper 2 cytokines that facilitate persistence of parasites and disease progression. In addition, some studies have also indicated that CD8⁺ T cells play a vital role in immune defense through cytokine production and their cytotoxic activity and excessive production of proinflammatory mediators promote amplified recruitment of cells. This could be correlated with excessive inflammatory reaction and ultimately resulted in tissue destruction and development of immunopathogenesis. Thus, there are contradictions regarding the role of immune responses in protection and immunopathogenesis of CL disease. Therefore, the aim of this paper was to review the role of host immune response in protection and its contribution to disease severity for CL infection. In order to obtain more meaningful data regarding the nature of immune response to leishmania, further in-depth studies focused on immune modulation should be conducted to develop better therapeutic strategies.

THP-1 cells increase TNF-α production upon LPS + soluble human IgG co-stimulation supporting evidence for TLR4 and Fcγ receptors crosstalk

The lipopolysaccharide (LPS) of Gram-negative bacteria is recognized on human monocytes and macrophages by TLR4 and MD2 and induces the production of inflammatory cytokines; the LPS + IgG complexes co-stimulation increases the cytokine production, mediated by the Fc-γRIIa (CD32a). We stimulated human CD14 + monocytes or THP-1 cells with LPS or LPS + soluble human IgG (sIgG) and TNF-α transcription and production, assessed RT-qPCR, ELISA, or flow cytometry, was enhanced by 30% upon LPS + sIgG compared to LPS stimulation. LPS + sIgG co-stimulation affected the NF-κB pathway (p65 phosphorylation and nucleus translocation, and IkB- α degradation). The biochemical inhibition of IRAK 1/4 and Syk kinases suppressed the enhancer effect of LPS + sIgG on TNF- α production, suggesting the involvement of both MyD88 dependent and independent pathways. Our results suggest that during LPS activation, sIgG may participate in a TLR4 - Fc-γR crosstalk.

Combination of Mycobacterium indicus pranii and Heat-Induced Promastigotes Cures Drug-Resistant Leishmania Infection: Critical Role of Interleukin-6-Producing Classical Dendritic Cells

The major issues in available therapeutic modalities against leishmaniasis are cost, toxicity, and the emergence of drug resistance. The aim of this work was to develop a successful therapeutic adjuvant against drug-resistant Leishmania donovani infection by means of combining Mycobacterium indicus pranii with heat-induced promastigotes (HIP). One-month postinfected BALB/c mice were administered subcutaneously with M. indicus pranii (10⁸ cells) and HIP (100 μg) for 5 days. Spleens were harvested for flow cytometric and reverse transcriptase PCR analysis. The antileishmanial effect of the combination strategy was associated with induction of a disease-resolving Th1 and Th17 response with simultaneous downregulation of CD4⁺ CD25⁺ Foxp3⁺ (nTreg) cells and CD4⁺ CD25^- Foxp3^- (Tr1) cells in the spleen. The significant expansion of CD4⁺ T_CM (CD4⁺ CD44^hi CD11a^hi CD62L^hi) cells was a further interesting outcome of this therapeutic strategy in the context of long-term protection of hosts against secondary infection. Toll-like receptor 2 (TLR2) was also found instrumental in this antiparasitic therapy. Induced interleukin-6 (IL-6) production from expanded CD11c⁺ CD8α⁺ (cDC1) and CD11c⁺ CD11b⁺ (cDC2) dendritic cells (DCs) but not from the CD11b⁺ Ly6c⁺ inflammatory monocytes (iMOs), was found critical in the protective expansion of Th17 as evidenced by an in vivo IL-6 neutralization assay. It also promoted the hematopoietic conversion toward DC progenitors (pre-DCs) from common dendritic cell progenitors (CDPs), the immediate precursors, in bone marrow. This novel combinational strategy demonstrated that expansion of Th17 by IL-6 released from CD11c⁺ classical DCs is crucial, together with the conventional Th1 response, to control drug-resistant infection.

Changes in the Expression of TLR2 During the Intestinal Phase of Trichinellosis

Introduction

Toll-like receptors (TLRs) play an important role in fast activation of the immune response to a variety of pathogens, including parasites. In this study, we focused on TLR2, because this receptor is one of the best known and most frequently analysed members of the TLR family. The aim of this study was to assess the effect of Trichinella spiralis on expression of TLR2 during the intestinal stage of infection.

Material and Methods

The experimental material consisted of isolates prepared from the intestines (jejunum and colon) of BALB/c mice infected with T. spiralis taken at 4, 8, and 16 days post infection.

Results

Our results based on quantitative real-time PCR showed that the mRNA level for TLR2 was statistically significantly higher in the jejuna of mice infected with T. spiralis than in this tissue of uninfected mice. In addition, the presence of TLR2 protein in the intestinal phase of trichinellosis was confirmed by a strong positive immunohistochemical reaction.

Conclusion

Our results indicate that infection with T. spiralis changes the expression of TLR2 in the small intestine of the mouse host and suggest a contribution of these receptors to the host defence mechanisms during experimental trichinellosis.

Expression of TLR2, TLR3, TLR4, and TLR7 on pulmonary lymphocytes of Schistosoma japonicum-infected C57BL/6 mice

Despite the paramount role of TLRs in the induction of innate immune and inflammatory responses, there is a paucity of studies on the role of TLRs in Schistosoma japonicum infection. Here, we observed obvious infiltration of inflammatory cells in S. japonicum-infected C57BL/6 mouse lungs. Expression and release of IFN-γ, IL-4, and IL-17 were significantly higher in pulmonary lymphocytes from infected mice compared with control mice in response to anti-CD3 plus anti-CD28 mAbs. Higher percentages of TLR2, TLR3, TLR4, and TLR7 were expressed on such lymphocytes, and the TLR agonists PGN, Poly I:C, LPS, and R848 induced a higher level of IFN-γ. However, a higher level of IL-4 was found in the supernatant of pulmonary lymphocytes from infected mice stimulated by these TLR agonists plus CD3 Ab. Only R848 plus anti-CD3 mAb could induce a higher level of IFN-γ in such lymphocytes. TLR expressions were then compared on different pulmonary lymphocytes after infection, including T cells, B cells, NK cells, NKT cells, and γδT cells. The expression levels of TLR3 on T cells, B cells, NK cells, and γδT cells were increased in the lungs after infection. NK cells also expressed higher levels of TLR4 after infection of control mice. Collectively, these findings highlight the potential role of TLR expression in the context of S. japonicum infection.

MicroRNA exporter HuR clears the internalized pathogens by promoting pro-inflammatory response in infected macrophages

HuR is a miRNA derepressor protein that can act as miRNA sponge for specific miRNAs to negate their action on target mRNAs. Here we have identified how HuR, by inducing extracellular vesicles‐mediated export of miRNAs, ensures robust derepression of miRNA‐repressed cytokines essential for strong pro‐inflammatory response in activated mammalian macrophages. Leishmania donovani, the causative agent of visceral leishmaniasis, on the contrary alters immune response of the host macrophage by a variety of complex mechanisms to promote anti‐inflammatory response essential for the survival of the parasite. We have found that during Leishmania infection, the pathogen targets HuR to promote onset of anti‐inflammatory response in mammalian macrophages. In infected macrophages, Leishmania also upregulate protein phosphatase 2A that acts on Ago2 protein to keep it in dephosphorylated and miRNA‐associated form. This causes robust repression of the miRNA‐targeted pro‐inflammatory cytokines to establish an anti‐inflammatory response in infected macrophages. HuR has an inhibitory effect on protein phosphatase 2A expression, and mathematical modelling of macrophage activation process supports antagonistic miRNA‐modulatory roles of HuR and protein phosphatase 2A which mutually balances immune response in macrophage by targeting miRNA function. Supporting this model, ectopic expression of the protein HuR and simultaneous inhibition of protein phosphatase 2A induce strong pro‐inflammatory response in the host macrophage to prevent the virulent antimonial drug‐sensitive or drug‐resistant form of L. donovani infection. Thus, HuR can act as a balancing factor of immune responses to curtail the macrophage infection process by the protozoan parasite.

Overview of the role of kinetoplastid surface carbohydrates in infection and host cell invasion: prospects for therapeutic intervention

Kinetoplastid parasites are responsible for serious diseases in humans and livestock such as Chagas disease and sleeping sickness (caused by Trypanosoma cruzi and Trypanosoma brucei, respectively), and the different forms of cutaneous, mucocutaneous and visceral leishmaniasis (produced by Leishmania spp). The limited number of antiparasitic drugs available together with the emergence of resistance underscores the need for new therapeutic agents with novel mechanisms of action. The use of agents binding to surface glycans has been recently suggested as a new approach to antitrypanosomal design and a series of peptidic and non-peptidic carbohydrate-binding agents have been identified as antiparasitics showing efficacy in animal models of sleeping sickness. Here we provide an overview of the nature of surface glycans in three kinetoplastid parasites, T. cruzi, T. brucei and Leishmania. Their role in virulence and host cell invasion is highlighted with the aim of identifying specific glycan-lectin interactions and carbohydrate functions that may be the target of novel carbohydrate-binding agents with therapeutic applications.

Systems analysis-based assessment of post-treatment adverse events in lymphatic filariasis

Background

Lymphatic filariasis (LF) is a neglected tropical disease, and the Global Program to Eliminate LF delivers mass drug administration (MDA) to 500 million people every year. Adverse events (AEs) are common after LF treatment.

Methodology/Principal findings

To better understand the pathogenesis of AEs, we studied LF-patients from a treatment trial. Plasma levels of many filarial antigens increased post-treatment in individuals with AEs, and this is consistent with parasite death. Circulating immune complexes were not elevated in these participants, and the classical complement cascade was not activated. Multiple cytokines increased after treatment in persons with AEs. A transcriptomic analysis was performed for nine individuals with moderate systemic AEs and nine matched controls. Differential gene expression analysis identified a significant transcriptional signature associated with post-treatment AEs; 744 genes were upregulated. The transcriptional signature was enriched for TLR and NF-κB signaling. Increased expression of seven out of the top eight genes upregulated in persons with AEs were validated by qRT-PCR, including TLR2.

Conclusions/Significance

This is the first global study of changes in gene expression associated with AEs after treatment of lymphatic filariasis. Changes in cytokines were consistent with prior studies and with the RNAseq data. These results suggest that Wolbachia lipoprotein is involved in AE development, because it activates TLR2-TLR6 and downstream NF-κB. Additionally, LPS Binding Protein (LBP, which shuttles lipoproteins to TLR2) increased post-treatment in individuals with AEs. Improved understanding of the pathogenesis of AEs may lead to improved management, increased MDA compliance, and accelerated LF elimination.

Lymphatic filariasis (LF) is a disabling parasitic disease that affects millions of people in the developing world. The Global Programme to Eliminate Lymphatic Filariasis (coordinated by the World Health Organization) uses mass administration of antifilarial medications to cure infections, prevent disease, and reduce transmission. Some individuals develop adverse events (AEs) after treatment, and this can reduce willingness of persons in endemic areas to accept treatment. The purpose of this study was to improve understanding of the cause of AEs following treatment. We hypothesized that parasite antigens released into the blood following treatment trigger inflammatory responses that lead to AEs. To test this hypothesis we collected blood from LF-infected individuals before and after treatment and clinically assessed them for AEs. We measured parasite antigens, cytokines and other components of the immune system in blood samples and compared post-treatment changes in persons with and without AEs. We also assessed changes in transcription profiles in peripheral blood leukocytes that were associated with post-treatment AEs. Post-treatment changes in transcription profiles and in immune proteins and parasite components in plasma suggest that systemic AEs are triggered by death of the parasites following treatment with release of parasite antigens and Wolbachia bacteria into the circulation. Improved understanding of the pathogenesis of post-treatment AEs may help to improve messaging related to mass drug administration programs and lead to improved AE management.