Modulation of Host-Pathogen Communication by Extracellular Vesicles (EVs) of the Protozoan Parasite Leishmania

An in-depth exploration of the multifaceted roles of EVs in the context of pathogenic single-cell microorganisms

SUMMARYExtracellular vesicles (EVs) have been recognized throughout scientific communities as potential vehicles of intercellular communication in both eukaryotes and prokaryotes, thereby influencing various physiological and pathological functions of both parent and recipient cells. This review provides an in-depth exploration of the multifaceted roles of EVs in the context of bacteria and protozoan parasite EVs, shedding light on their contributions to physiological processes and disease pathogenesis. These studies highlight EVs as a conserved mechanism of cellular communication, which may lead us to important breakthroughs in our understanding of infection, mechanisms of pathogenesis, and as indicators of disease. Furthermore, EVs are involved in host-microbe interactions, offering insights into the strategies employed by bacteria and protozoan parasites to modulate host responses, evade the immune system, and establish infections.

Live attenuated-nonpathogenic Leishmania and DNA structures as promising vaccine platforms against leishmaniasis: innovations can make waves

Leishmaniasis is a vector-borne disease caused by the protozoan parasite of Leishmania genus and is a complex disease affecting mostly tropical regions of the world. Unfortunately, despite the extensive effort made, there is no vaccine available for human use. Undoubtedly, a comprehensive understanding of the host-vector-parasite interaction is substantial for developing an effective prophylactic vaccine. Recently the role of sandfly saliva on disease progression has been uncovered which can make a substantial contribution in vaccine design. In this review we try to focus on the strategies that most probably meet the prerequisites of vaccine development (based on the current understandings) including live attenuated/non-pathogenic and subunit DNA vaccines. Innovative approaches such as reverse genetics, CRISP/R-Cas9 and antibiotic-free selection are now available to promisingly compensate for intrinsic drawbacks associated with these platforms. Our main goal is to call more attention toward the prerequisites of effective vaccine development while controlling the disease outspread is a substantial need.

Subcellular particles for characterization of host-parasite interactions

Parasitic diseases remain a major global health problem for humans. Parasites employ a variety of strategies to invade and survive within their hosts and to manipulate host defense mechanisms, always in the pathogen's favor. Extracellular vesicles (EVs), membrane-bound nanospheres carrying a variety of bioactive compounds, were shown to be released by the parasites during all stages of the infection, enabling growth and expansion within the host and adaptation to frequently changing environmental stressors. In this review, we discuss how the use of existing nanotechnologies and high-resolution imaging tools assisted in revealing the role of EVs during parasitic infections, enabling the quantitation, visualization, and detailed characterization of EVs. We discuss here the cases of malaria, Chagas disease and leishmaniasis as examples of parasitic neglected tropical diseases (NTDs). Unraveling the EVs' role in the NTD pathogenesis may enormously contribute to their early and reliable diagnostic, effective treatment, and prevention.

Extracellular Vesicles from Leishmania (Leishmania) infantum Contribute in Stimulating Immune Response and Immunosuppression in Hosts with Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a chronic systemic disease. In Brazil this infection is caused by Leishmania (Leishmania) infantum. Extracellular vesicles (EVs) released by Leishmania species have different functions like the modulation of host immune systems and inflammatory responses, among others. This study evaluated the participation of EVs from L. (L.) infantum (Leish-EVs) in recognition of the humoral and cellular immune response of hosts with VL. Promastigotes were cultivated in 199 medium and, in the log phase of growth, they were centrifuged, washed, resus-pended in RPMI medium, and incubated for 2 to 24 h, at 25 °C or 37 °C to release Leish-EVs. This dynamic was evaluated using transmission (TEM) and scanning (SEM) electron microscopies, as well as nanoparticle tracking analysis (NTA). The results suggested that parasite penetration in mammal macrophages requires more Leish-EVs than those living in insect vectors, since promastigotes incubated at 37 °C released more Leish-EVs than those incubated at 25 °C. Infected THP-1 cells produced high EV concentration (THP-1 cells-EVs) when compared with those from the control group. The same results were obtained when THP-1 cells were treated with Leish-EVs or a crude Leishmania antigen. These data indicated that host-EV concentrations could be used to distinguish infected from uninfected hosts. THP-1 cells treated with Leish-EVs expressed more IL-12 than control THP-1 cells, but were unable to express IFN-γ. These same cells highly expressed IL-10, which inhibited TNF-α and IL-6. Equally, THP-1 cells treated with Leish-EVs up-expressed miR-21-5p and miR-146a-5p. In conclusion, THP-1 cells treated with Leish-EVs highly expressed miR-21-5p and miR-146a-5p and caused the dysregulation of IL-10. Indirectly, these results suggest that high expression of these miRNAs species is caused by Leish-EVs. Consequently, this molecular via can contribute to immunosuppression causing enhanced immunopathology in infected hosts.

Evidence of a conserved mammalian immunosuppression mechanism in Lutzomyia longipalpis upon infection with Leishmania

Introduction

Sand flies (Diptera: Phlebotominae) belonging to the Lutzomyia genus transmit Leishmania infantum parasites. To understand the complex interaction between the vector and the parasite, we have been investigating the sand fly immune responses during the Leishmania infection. Our previous studies showed that genes involved in the IMD, Toll, and Jak-STAT immunity pathways are regulated upon Leishmania and bacterial challenges. Nevertheless, the parasite can thrive in the vectors' gut, indicating the existence of mechanisms capable of modulating the vector defenses, as was already seen in mammalian Leishmania infections.

Methods results and discussion

In this study, we investigated the expression of Lutzomyia longipalpis genes involved in regulating the Toll pathway under parasitic infection. Leishmania infantum infection upregulated the expression of two L. longipalpis genes coding for the putative repressors cactus and protein tyrosine phosphatase SHP. These findings suggest that the parasite can modulate the vectors' immune response. In mammalian infections, the Leishmania surface glycoprotein GP63 is one of the inducers of host immune depression, and one of the known effectors is SHP. In L. longipalpis we found a similar effect: a genetically modified strain of Leishmania amazonensis over-expressing the metalloprotease GP63 induced a higher expression of the sand fly SHP indicating that the L. longipalpis SHP and parasite GP63 increased expressions are connected. Immuno-stained microscopy of L. longipalpis LL5 embryonic cells cultured with Leishmania strains or parasite conditioned medium showed cells internalization of parasite GP63. A similar internalization of GP63 was observed in the sand fly gut tissue after feeding on parasites, parasite exosomes, or parasite conditioned medium, indicating that GP63 can travel through cells in vitro or in vivo. When the sand fly SHP gene was silenced by RNAi and females infected by L. infantum, parasite loads decreased in the early phase of infection as expected, although no significant differences were seen in late infections of the stomodeal valve.

Conclusions

Our findings show the possible role of a pathway repressor involved in regulating the L. longipalpis immune response during Leishmania infections inside the insect. In addition, they point out a conserved immunosuppressive effect of GP63 between mammals and sand flies in the early stage of parasite infection.

Guidelines for the purification and characterization of extracellular vesicles of parasites

Parasites are responsible for the most neglected tropical diseases, affecting over a billion people worldwide (WHO, 2015) and accounting for billions of cases a year and responsible for several millions of deaths. Research on extracellular vesicles (EVs) has increased in recent years and demonstrated that EVs shed by pathogenic parasites interact with host cells playing an important role in the parasite's survival, such as facilitation of infection, immunomodulation, parasite adaptation to the host environment and the transfer of drug resistance factors. Thus, EVs released by parasites mediate parasite-parasite and parasite-host intercellular communication. In addition, they are being explored as biomarkers of asymptomatic infections and disease prognosis after drug treatment. However, most current protocols used for the isolation, size determination, quantification and characterization of molecular cargo of EVs lack greater rigor, standardization, and adequate quality controls to certify the enrichment or purity of the ensuing bioproducts. We are now initiating major guidelines based on the evolution of collective knowledge in recent years. The main points covered in this position paper are methods for the isolation and molecular characterization of EVs obtained from parasite-infected cell cultures, experimental animals, and patients. The guideline also includes a discussion of suggested protocols and functional assays in host cells.

Amphotericin B-Loaded Extracellular Vesicles Derived from Leishmania major Enhancing Cutaneous Leishmaniasis Treatment through In Vitro and In Vivo Studies

Background

Recent studies have shown an increasing number of patients with cutaneous leishmaniasis (CL) who do not respond to pentavalent antimonials as the first line of treatment for CL. Nanocarriers such as extracellular vesicles (EVs) are efficient vehicles that might be used as drug delivery systems for the treatment of diseases. Therefore, we aimed to isolate and characterize the EVs of Leishmania major, load them with Amphotericin B (AmB), and investigate the toxicity and efficacy of the prepared drug form.

Methods

The EVs of L. major were isolated, characterized, and loaded with amphotericin B (AmB), and the EVs-Amphotericin B (EVs-AmB) form was synthesized. Relevant in vitro and in vivo methods were performed to evaluate the toxicity and efficacy of EVs-AmB compared to the control.

Results

The anti-leishmanial activity of the EVs-AmB showed a higher percentage inhibition (PI%) (P = 0.023) compared to the AmB at different concentrations and time points. Obtained data showed a significant increase in the lesion size and parasite load in the lesion, PBS, and EVs mice groups in comparison with EVs-AmB, AmB, and Glucantime groups (P < 0.05), EVs-AmB had a significant decrease in lesion sizes in comparison with AmB (P < 0.05). Results showed that EVs-AmB decreased its toxicity to the kidneys and liver (P < 0.05).

Conclusion

EVs-AmB improved the efficacy of AmB in mouse skin lesions and reduced hepatorenal toxicity. Furthermore, EVs could be a promising nanoplatform for the delivery of AmB in CL caused by L. major.

The characterization of RNA-binding proteins and RNA metabolism-related proteins in fungal extracellular vesicles

RNA-binding proteins (RBPs) are essential for regulating RNA metabolism, stability, and translation within cells. Recent studies have shown that RBPs are not restricted to intracellular functions and can be found in extracellular vesicles (EVs) in different mammalian cells. EVs released by fungi contain a variety of proteins involved in RNA metabolism. These include RNA helicases, which play essential roles in RNA synthesis, folding, and degradation. Aminoacyl-tRNA synthetases, responsible for acetylating tRNA molecules, are also enriched in EVs, suggesting a possible link between these enzymes and tRNA fragments detected in EVs. Proteins with canonical RNA-binding domains interact with proteins and RNA, such as the RNA Recognition Motif (RRM), Zinc finger, and hnRNP K-homology (KH) domains. Polyadenylate-binding protein (PABP) plays a critical role in the regulation of gene expression by binding the poly(A) tail of messenger RNA (mRNA) and facilitating its translation, stability, and localization, making it a key factor in post-transcriptional control of gene expression. The presence of proteins related to the RNA life cycle in EVs from different fungal species suggests a conserved mechanism of EV cargo packing. Various models have been proposed for selecting RNA molecules for release into EVs. Still, the actual loading processes are unknown, and further molecular characterization of these proteins may provide insight into the mechanism of RNA sorting into EVs. This work reviews the current knowledge of RBPs and proteins related to RNA metabolism in EVs derived from distinct fungi species, and presents an analysis of proteomic datasets through GO term and orthology analysis, Our investigation identified orthologous proteins in fungal EVs on different fungal species.

Naegleria fowleri Extracellular Vesicles Induce Proinflammatory Immune Responses in BV-2 Microglial Cells

Extracellular vesicles (EVs) of protozoan parasites have diverse biological functions that are essential for parasite survival and host-parasite interactions. In this study, we characterized the functional properties of EVs from Naegleria fowleri, a pathogenic amoeba that causes a fatal brain infection called primary amoebic meningoencephalitis (PAM). N. fowleri EVs (NfEVs) have been shown to be internalized by host cells such as C6 glial cells and BV-2 microglial cells without causing direct cell death, indicating their potential roles in modulating host cell functions. NfEVs induced increased expression of proinflammatory cytokines and chemokines such as TNF-α, IL-1α, IL-1β, IL-6, IL-17, IFN-γ, MIP-1α, and MIP-2 in BV-2 microglial cells; these increases were initiated via MyD88-dependent TLR-2/TLR-4. The production levels of proinflammatory cytokines and chemokines in NfEVs-stimulated BV-2 microglial cells were effectively downregulated by inhibitors of MAPK, NF-κB, or JAK-STAT. Phosphorylation levels of JNK, p38, ERK, p65, JAK-1, and STAT3 were increased in NfEVs-stimulated BV-2 microglial cells but were effectively suppressed by each corresponding inhibitor. These results suggest that NfEVs could induce proinflammatory immune responses in BV-2 microglial cells via the NF-κB-dependent MAPK and JAK-STAT signaling pathways. Taken together, these findings suggest that NfEVs are pathogenic factors involved in the contact-independent pathogenic mechanisms of N. fowleri by inducing proinflammatory immune responses in BV-2 microglial cells, further contributing to deleterious inflammation in infected foci by activating subsequent inflammation cascades in other brain cells.

Exosome-derived long noncoding RNAs: Mediators of host-Plasmodium parasite communication

Overcoming challenges associated with malaria eradication proves to be a formidable task due to the complicated life cycle exhibited by the malaria parasite and the lack of safe and enduring vaccines against malaria. Investigating the interplay between Plasmodium parasites and their mammalian hosts is crucial for the development of novel vaccines. Long noncoding RNAs (lncRNAs) derived from Plasmodium parasites or host cells have emerged as potential signaling molecules involved in the trafficking of proteins, RNA (mRNAs, miRNAs, and ncRNAs), and DNA. These lncRNAs facilitate the interaction between hosts and parasites, impacting normal physiology or pathology in malaria-infected individuals. Moreover, they possess the capacity to regulate immune responses and associated signaling pathways, thus potentially influencing chromatin organization, epigenetic modifications, mRNA processing, splicing, and translation. However, the functional role of exosomal lncRNAs in malaria remains poorly understood. This review offers a comprehensive analysis of lncRNA and exosomal lncRNA profiles during malaria infection. It presents an overview of recent progress in elucidating the involvement of exosomal lncRNAs in host-parasite interactions. Additionally, potential exosomal lncRNAs linked to the domains of innate and adaptive immunity in the context of malaria are proposed. These findings may contribute to the discovery of new diagnostic and therapeutic strategies for malaria. Furthermore, the need for additional research was highlighted that aimed to elucidate the mechanisms underlying lncRNA transportation into host cells and their targeting of specific genes to regulate the host's immune response. This knowledge gap presents an opportunity for future investigations, offering innovative approaches to enhance malarial control. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Small Molecule-RNA Interactions RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA in Disease and Development > RNA in Disease.

Non-Vesicular Lipid Transport Machinery in Leishmania donovani: Functional Implications in Host-Parasite Interaction

Eukaryotic cells have distinct membrane-enclosed organelles, each with a unique biochemical signature and specialized function. The unique identity of each organelle is greatly governed by the asymmetric distribution and regulated intracellular movement of two important biomolecules, lipids, and proteins. Non-vesicular lipid transport mediated by lipid-transfer proteins (LTPs) plays essential roles in intra-cellular lipid trafficking and cellular lipid homeostasis, while vesicular transport regulates protein trafficking. A comparative analysis of non-vesicular lipid transport machinery in protists could enhance our understanding of parasitism and basis of eukaryotic evolution. Leishmania donovani, the trypanosomatid parasite, greatly depends on receptor-ligand mediated signalling pathways for cellular differentiation, nutrient uptake, secretion of virulence factors, and pathogenesis. Lipids, despite being important signalling molecules, have intracellular transport mechanisms that are largely unexplored in L. donovani. We have identified a repertoire of sixteen (16) potential lipid transfer protein (LTP) homologs based on a domain-based search on TriTrypDB coupled with bioinformatics analyses, which signifies the presence of well-organized lipid transport machinery in this parasite. We emphasized here their evolutionary uniqueness and conservation and discussed their potential implications for parasite biology with regards to future therapeutic targets against visceral leishmaniasis.

Novel Technologies for Exosome and Exosome-like Nanovesicle Procurement and Enhancement

Exosomes are extracellular nanovesicles commonly produced by mammalian cells that in recent years have risen as a novel strategy for drug delivery systems and cancer therapy because of their innate specificity and high bioavailability. However, there are limitations that undermine their potential. Among them is the lack of mass production capacity with the current available sources and the failure to reach the intended therapeutic effect because of their insufficient uptake or their rapid clearance once administered. This review aims to show the current advances in overcoming these limitations by presenting, firstly, reported strategies to improve exosome and exosome-like nanovesicle extraction from possible novel eukaryotic sources, including animals, plants, and protozoa; and secondly, alternative modification methods that functionalize exosomes by conferring them higher targeting capacity and protection from organism defenses, which results in an increase in the attachment of ligands and cellular uptake of inorganic materials. However, even when these strategies might address some of the obstacles in their procurement and therapeutic use, there are still several aspects that need to be addressed, so several perspectives of the matter are also presented and analyzed throughout this work.

Insights on Host-Parasite Immunomodulation Mediated by Extracellular Vesicles of Cutaneous Leishmania shawi and Leishmania guyanensis

Leishmaniasis is a parasitic disease caused by different species of Leishmania and transmitted through the bite of sand flies vector. Macrophages (MΦ), the target cells of Leishmania parasites, are phagocytes that play a crucial role in the innate immune microbial defense and are antigen-presenting cells driving the activation of the acquired immune response. Exploring parasite-host communication may be key in restraining parasite dissemination in the host. Extracellular vesicles (EVs) constitute a group of heterogenous cell-derived membranous structures, naturally produced by all cells and with immunomodulatory potential over target cells. This study examined the immunogenic potential of EVs shed by L. shawi and L. guyanensis in MΦ activation by analyzing the dynamics of major histocompatibility complex (MHC), innate immune receptors, and cytokine generation. L. shawi and L. guyanensis EVs were incorporated by MΦ and modulated innate immune receptors, indicating that EVs cargo can be recognized by MΦ sensors. Moreover, EVs induced MΦ to generate a mix of pro- and anti-inflammatory cytokines and favored the expression of MHCI molecules, suggesting that EVs antigens can be present to T cells, activating the acquired immune response of the host. Since nano-sized vesicles can be used as vehicles of immune mediators or immunomodulatory drugs, parasitic EVs can be exploited by bioengineering approaches for the development of efficient prophylactic or therapeutic tools for leishmaniasis.

Biogenesis of extracellular vesicles in protozoan parasites: The ESCRT complex in the trafficking fast lane?

Extracellular vesicles (EVs) provide a central mechanism of cell-cell communication. While EVs are found in most organisms, their pathogenesis-promoting roles in parasites are of particular interest given the potential for medical insight and consequential therapeutic intervention. Yet, a key feature of EVs in human parasitic protozoa remains elusive: their mechanisms of biogenesis. Here, we survey the current knowledge on the biogenesis pathways of EVs secreted by the four main clades of human parasitic protozoa: apicomplexans, trypanosomatids, flagellates, and amoebae. In particular, we shine a light on findings pertaining to the Endosomal Sorting Complex Required for Transport (ESCRT) machinery, as in mammals it plays important roles in EV biogenesis. This review highlights the diversity in EV biogenesis in protozoa, as well as the related involvement of the ESCRT system in these unique organisms.

Leishmania Vesicle-Depleted Exoproteome: What, Why, and How?

Leishmaniasis, a vector-borne parasitic protozoan disease, is among the most important neglected tropical diseases. In the absence of vaccines, disease management is challenging. The available chemotherapy is suboptimal, and there are growing concerns about the emergence of drug resistance. Thus, a better understanding of parasite biology is essential to generate new strategies for disease control. In this context, in vitro parasite exoproteome characterization enabled the identification of proteins involved in parasite survival, pathogenesis, and other biologically relevant processes. After 2005, with the availability of genomic information, these studies became increasingly feasible and revealed the true complexity of the parasite exoproteome. After the discovery of Leishmania extracellular vesicles (EVs), most exoproteome studies shifted to the characterization of EVs. The non-EV portion of the exoproteome, named the vesicle-depleted exoproteome (VDE), has been mostly ignored even if it accounts for a significant portion of the total exoproteome proteins. Herein, we summarize the importance of total exoproteome studies followed by a special emphasis on the available information and the biological relevance of the VDE. Finally, we report on how VDE can be studied and disclose how it might contribute to providing biologically relevant targets for diagnosis, drug, and vaccine development.

The state of the art of extracellular vesicle research in protozoan infection

Protozoan diseases seriously affect the health of human beings, livestock and poultry and lead to high economic and medical costs. Extracellular vesicles (EVs) are membranous structures formed through biological processes that play important roles in immune regulation. Studies have shown that parasites transmit information to hosts through EVs to modulate host immune responses. The major roles played by EVs released from parasites involve facilitating parasitization of the host. In this review, we discuss relevant recently obtained data on EVs secreted by different kinds of protozoa, including their molecular mechanisms, and discuss the roles played by EVs in the occurrence and development of parasitic diseases.

Isolation, characterization, and functional study of extracellular vesicles derived from Leishmania tarentolae

Leishmania (L.) species are protozoan parasites with a complex life cycle consisting of a number of developmental forms that alternate between the sand fly vector and their host. The non-pathogenic species L. tarentolae is not able to induce an active infection in a human host. It has been observed that, in pathogenic species, extracellular vesicles (EVs) could exacerbate the infection. However, so far, there is no report on the identification, isolation, and characterization of L. tarentolae EVs. In this study, we have isolated and characterized EVs from L. tarentolaeGFP+ (tEVs) along with L. majorGFP+ as a reference and positive control. The EVs secreted by these two species demonstrated similar particle size distribution (approximately 200 nm) in scanning electron microscopy and nanoparticle tracking analysis. Moreover, the said EVs showed similar protein content, and GFP and GP63 proteins were detected in both using dot blot analysis. Furthermore, we could detect Leishmania-derived GP63 protein in THP-1 cells treated with tEVs. Interestingly, we observed a significant increase in the production of IFN-γ, TNF-α, and IL-1β, while there were no significant differences in IL-6 levels in THP-1 cells treated with tEVs following an infection with L. major compared with another group of macrophages that were treated with L. major EVs prior to the infection. Another exciting observation of this study was a significant decrease in parasite load in tEV-treated Leishmania-infected macrophages. In addition, in comparison with another group of Leishmania-infected macrophages which was not exposed to any EVs, tEV managed to increase IFN-γ and decrease IL-6 and the parasite burden. In conclusion, we report for the first time that L. tarentolae can release EVs and provide evidence that tEVs are able to control the infection in human macrophages, making them a great potential platform for drug delivery, at least for parasitic infections.

Extracellular vesicles from Trichinella spiralis: Proteomic analysis and protective immunity

Trichinella spiralis (T. spiralis) derived extracellular vesicles (EVs) have been proposed to play a key role in regulating the host immune responses. In this study, we provided the first investigation of EVs proteomics released by T. spiralis muscle larvae (ML). T. spiralis ML EVs (Ts-ML-EVs) were successfully isolated and characterized by transmission electron microscopy (TEM) and western blotting. Using liquid chromatograph mass spectrometer (LC-MS/MS) analysis, we identified 753 proteins in the Ts-ML-EVs proteome and annotated by gene ontology (GO). These proteins were enriched in different categories by GO, kyoto encyclopedia of genes and genomes (KEGG) and domain analysis. GO enrichment analysis indicated association of protein deglutathionylation, lysosomal lumen and serine-type endopeptidase inhibitor activity with proteins which may be helpful during parasite-host interaction. Moreover, KEGG enrichment analysis revealed involvement of Ts-ML-EVs proteins in other glycan degradation, complement and coagulation cascades, proteasome and various metabolism pathways. In addition, BALB/c mice were immunized by subcutaneous injection of purified Ts-ML-EVs. Ts-ML-EVs group demonstrated a 23.4% reduction in adult worms and a 43.7% reduction in ML after parasite challenge. Cellular and humoral immune responses induced by Ts-ML-EVs were detected, including the levels of specific antibodies (IgG, IgM, IgE, IgG1 and IgG2a) as well as cytokines (IL-12, IFN-γ, IL-4 and IL-10) in serum. The results showed that Ts-ML-EVs could induce a Th1/Th2 mixed immune response with Th2 predominant. This study revealed a potential role of Ts-ML-EVs in T. spiralis biology, particularly in the interaction with host. This work provided a critical step to against T. spiralis infection based on Ts-ML-EVs.

Extracellular vesicles (EVs) play an important role in cell-cell communication. They can transport functional molecules to target tissues and cells. During parasite infection, EVs provide suitable diagnostic makers and vaccine antigens for as well as inducing host immune responses. In Trichinella spiralis (T. spiralis), we previous proved that Ts-ML-EVs exerted immunomodulatory effect that inhibited experimental colitis in mice. Based on these results, we tested the protein composition of Ts-ML-EVs and the immune protective effect of Ts-ML-EVs. Our study showed that Ts-ML-EVs contained a number of immune-related proteins and it could be potential vaccine antigen for preventing T. spiralis infection.

A recombinant Leishmania amastigote-specific protein, rLiHyG, with adjuvants, protects against infection with Leishmania infantum

Vaccination against visceral leishmaniasis (VL) should be considered as a control measure to protect against disease, and amastigote-specific proteins could help to develop such vaccines, since this parasite form is in contact with the host immune system during the active disease. In this study, a Leishmania amastigote-specific protein, LiHyG, was evaluated as recombinant protein (rLiHyG) as vaccine candidate against Leishmania infantum infection in BALB/c mice. The protein was associated with saponin (rLiHyG/Sap) or Poloxamer 407-based polymeric micelles (rLiHyG/Mic) as adjuvants, and animals receiving saline, saponin or micelle as controls. Immunological and parasitological analyses were performed before (n = 8 per group; as primary endpoint) and after (n = 8 per group; as secondary endpoint) infection. Results showed that, in both endpoints, rLiHyG/Sap and rLiHyG/Mic induced higher levels of IFN-γ, IL-12 and GM-CSF in spleen cell cultures from vaccinated animals, besides elevated presence of IgG2a isotype antibodies. Decreased hepatotoxicity and 'positive lymphoproliferative response were also found after challenge. Such findings reflected in significantly lower levels of parasite load found in their spleens, livers, bone marrows and draining lymph nodes. In conclusion, rLiHyG associated with Th1-type adjuvant could be considered for future studies as vaccine candidate to protect against VL.

Double-Stranded RNA Viruses Are Released From Trichomonas vaginalis Inside Small Extracellular Vesicles and Modulate the Exosomal Cargo

Trichomonas vaginalis is a parasitic protist that infects the human urogenital tract. During the infection, trichomonads adhere to the host mucosa, acquire nutrients from the vaginal/prostate environment, and release small extracellular vesicles (sEVs) that contribute to the trichomonad adherence and modulate the host-parasite communication. Approximately 40–70% of T. vaginalis strains harbor a double-stranded RNA virus called Trichomonasvirus (TVV). Naked TVV particles have the potential to stimulate a proinflammatory response in human cells, however, the mode of TVV release from trichomonads to the environment is not clear. In this report, we showed for the first time that TVV particles are released from T. vaginalis cells within sEVs. The sEVs loaded with TVV stimulated a higher proinflammatory response of human HaCaT cells in comparison to sEVs from TVV negative parasites. Moreover, a comparison of T. vaginalis isogenic TVV plus and TVV minus clones revealed a significant impact of TVV infection on the sEV proteome and RNA cargo. Small EVs from TVV positive trichomonads contained 12 enriched and 8 unique proteins including membrane-associated BspA adhesine, and about a 2.5-fold increase in the content of small regulatory tsRNA. As T. vaginalis isolates are frequently infected with TVV, the release of TVV via sEVs to the environment represents an important factor with the potential to enhance inflammation-related pathogenesis during trichomoniasis.

Tackling Drug Resistance and Other Causes of Treatment Failure in Leishmaniasis

Leishmaniasis is a tropical infectious disease caused by the protozoan Leishmania parasite. The disease is transmitted by female sand flies and, depending on the infecting parasite species, causes either cutaneous (stigmatizing skin lesions), mucocutaneous (destruction of mucous membranes of nose, mouth and throat) or visceral disease (a potentially fatal infection of liver, spleen and bone marrow). Although more than 1 million new cases occur annually, chemotherapeutic options are limited and their efficacy is jeopardized by increasing treatment failure rates and growing drug resistance. To delay the emergence of resistance to existing and new drugs, elucidating the currently unknown causes of variable drug efficacy (related to parasite susceptibility, host immunity and drug pharmacokinetics) and improved use of genotypic and phenotypic tools to define, measure and monitor resistance in the field are critical. This review highlights recent progress in our understanding of drug action and resistance in Leishmania, ongoing challenges (including setbacks related to the COVID-19 pandemic) and provides an overview of possible strategies to tackle this public health challenge.

Differential translational regulation of host exosomal proteins play key role in immunomodulation in antimony resistance in Visceral Leishmaniasis: A proteomic profiling study

In host-pathogen interactions, exosomal secretions are crucial for cell to cell communication and have an established role in immunomodulation. Protozoans, including Leishmania, modulates their host vesicular secretions for better survival; although the role of exosomal secretions in unresponsive against sodium antimony gluconate (SAG) has never been documented. In this study, the exosomal proteome of RAW macrophages infected with either SAG responsive (SAG^S) or SAG unresponsive (SAG^R) L. donovani parasites has been compared with uninfected RAW macrophages. Proteins isolated from exosomes were labelled with iTRAQ reagents; followed by subsequent LC-TOF/-MS analysis. In total, 394 proteins (p < 0.05) were identified which were shared common among all sets. Highly differentially expressed proteins were sorted by log2 value -1 and +1 as down regulated and up regulated respectively which yielded 58 proteins in SAG^R and 41 proteins during SAG^S infection. Out of the 58 proteins identified during SAG^R infection, 17 proteins were of immune modulatory function. Network visualization model and pathway analysis revealed the interactions among these proteins via different immunological pathways with reported involvement of some proteins in SAG resistance and host immune modulation. Hence, the differential abundance of immune pathway related proteins in exosomes of infected host during SAG^R infection supports the immune modulatory strategy adopted by SAG resistant parasites for enhanced survival .

Long-Term In Vitro Passaging Had a Negligible Effect on Extracellular Vesicles Released by Leishmania amazonensis and Induced Protective Immune Response in BALB/c Mice

Depending on Leishmania species and the presence/absence of virulence factors, Leishmania extracellular vesicles (EVs) can differently stimulate host immune cells. This work is aimed at characterizing and evaluating the protective role of EVs released by Leishmania amazonensis promastigotes under different maintenance conditions. Initially, using a control strain, we standardized 26°C as the best release temperature to obtain EVs with a potential protective role in the experimental leishmaniasis model. Then, long-term (LT-P) promastigotes of L. amazonensis were obtained after long-term in vitro culture (100 in vitro passages). In vivo-derived (IVD-P) promastigotes of L. amazonensis were selected after 3 consecutive experimental infections in BALB/c mice. Those strains developed similar lesion sizes except for IVD-P at 8 weeks post infection. No differences in EV production were detected in both strains. However, the presence of LPG between LT-P and IVD-P EVs was different. Groups of mice immunized with EVs emulsified in the adjuvant and challenged with IVD-P parasites showed decreased lesion size and parasitic load compared with the nonimmunized groups. The immunization regimen with two doses showed high IFN-γ and IgG2a titers in challenged mice with either IVD-P or LT-P EVs. IL-4 and IL-10 were detected in immunized mice, suggesting a mixed Th1/Th2 profile. EVs released by either IVD-P or LT-P induced a partial protective effect in an immunization model. Thus, our results uncover a potential protective role of EVs from L. amazonensis for cutaneous leishmaniasis. Moreover, long-term maintenance under in vitro conditions did not seem to affect EV release and their immunization properties in mice.

Candidates for Balancing Selection in Leishmania donovani Complex Parasites

The Leishmania donovani species complex is the causative agent of visceral leishmaniasis, which cause 20–40,000 fatalities a year. Here, we conduct a screen for balancing selection in this species complex. We used 384 publicly available L. donovani and L. infantum genomes, and sequence 93 isolates of L. infantum from Brazil to describe the global diversity of this species complex. We identify five genetically distinct populations that are sufficiently represented by genomic data to search for signatures of selection. We find that signals of balancing selection are generally not shared between populations, consistent with transient adaptive events, rather than long-term balancing selection. We then apply multiple diversity metrics to identify candidate genes with robust signatures of balancing selection, identifying a curated set of 24 genes with robust signatures. These include zeta toxin, nodulin-like, and flagellum attachment proteins. This study highlights the extent of genetic divergence between L. donovani complex parasites and provides genes for further study.

Impact of the Extracellular Vesicles Derived From Trypanosoma cruzi: A Paradox in Host Response and Lipid Metabolism Modulation

Chagas disease is a major public health problem, especially in the South and Central America region. Its incidence is related to poverty and presents a high rate of morbidity and mortality. The pathogenesis of Chagas disease is complex and involves many interactive pathways between the hosts and the Trypanosoma cruzi. Several factors have been implicated in parasite-host interactions, including molecules secreted by infected cells, lipid mediators and most recent, extracellular vesicles (EVs). The EVs of T. cruzi (EVsT) were reported for the first time in the epimastigote forms about 42 years ago. The EVsT are involved in paracrine communication during the infection and can have an important role in the inflammatory modulation and parasite escape mechanism. However, the mechanisms by which EVs employ their pathological effects are not yet understood. The EVsT seem to participate in the activation of macrophages via TLR2 triggering the production of cytokines and a range of other molecules, thus modulating the host immune response which promotes the parasite survival. Moreover, new insights have demonstrated that EVsT induce lipid body formation and PGE₂ synthesis in macrophages. This phenomenon is followed by the inhibition of the synthesis of pro-inflammatory cytokines and antigen presentation, causing decreased parasitic molecules and allowing intracellular parasite survival. Therefore, this mini review aims to discuss the role of the EVs from T. cruzi as well as its involvement in the mechanisms that regulate the host immune response in the lipid metabolism and its significance for the Chagas disease pathophysiology.

Leishmania 360°: Guidelines for Exosomal Research

Leishmania parasites are a group of kinetoplastid pathogens that cause a variety of clinical disorders while maintaining cell communication by secreting extracellular vesicles. Emerging technologies have been adapted for the study of Leishmania-host cell interactions, to enable the broad-scale analysis of the extracellular vesicles of this parasite. Leishmania extracellular vesicles (LEVs) are spheroidal nanoparticles of polydispersed suspensions surrounded by a layer of lipid membrane. Although LEVs have attracted increasing attention from researchers, many aspects of their biology remain unclear, including their bioavailability and function in the complex molecular mechanisms of pathogenesis. Given the importance of LEVs in the parasite-host interaction, and in the parasite-parasite relationships that have emerged during the evolutionary history of these organisms, the present review provides an overview of the available data on Leishmania, and formulates guidelines for LEV research. We conclude by reporting direct methods for the isolation of specific LEVs from the culture supernatant of the promastigotes and amastigotes that are suitable for a range of different downstream applications, which increases the compatibility and reproducibility of the approach for the establishment of optimal and comparable isolation conditions and the complete characterization of the LEV, as well as the critical immunomodulatory events triggered by this important group of parasites.

Malaria parasites both repress host CXCL10 and use it as a cue for growth acceleration

Pathogens are thought to use host molecular cues to control when to initiate life-cycle transitions, but these signals are mostly unknown, particularly for the parasitic disease malaria caused by Plasmodium falciparum. The chemokine CXCL10 is present at high levels in fatal cases of cerebral malaria patients, but is reduced in patients who survive and do not have complications. Here we show a Pf 'decision-sensing-system' controlled by CXCL10 concentration. High CXCL10 expression prompts P. falciparum to initiate a survival strategy via growth acceleration. Remarkably, P. falciparum inhibits CXCL10 synthesis in monocytes by disrupting the association of host ribosomes with CXCL10 transcripts. The underlying inhibition cascade involves RNA cargo delivery into monocytes that triggers RIG-I, which leads to HUR1 binding to an AU-rich domain of the CXCL10 3'UTR. These data indicate that when the parasite can no longer keep CXCL10 at low levels, it can exploit the chemokine as a cue to shift tactics and escape.

Giardia duodenalis extracellular vesicles regulate the proinflammatory immune response in mouse macrophages in vitro via the MAPK, AKT and NF-κB pathways

Background

Giardia duodenalis is an extracellular protozoan parasite that causes giardiasis in mammals. The presentation of giardiasis ranges from asymptomatic to severe diarrhea, and the World Health Organization lists it in the Neglected Diseases Initiative. Extracellular vesicles (EVs) are a key mediator of intracellular communication. Although previous studies have shown that G. intestinalis can regulate a host’s innate immune response, the role of G. intestinalis EVs (GEVs) in triggering a G. intestinalis-induced innate immune response remains to be further explored.

Methods

In this study, GEVs, G. intestinalis and GEVs + G. intestinalis were inoculated into macrophages, respectively. The transcription and secretion levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6 and tumor necrosis factor alpha (TNF-α), were measured using real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assays (ELISAs). The phosphorylation levels of the MAPK, AKT and NF-κB signaling pathways in GEV-stimulated mouse macrophages were examined using western blotting and immunofluorescence methods. The roles of activated pathways in the GEV-triggered inflammatory response were determined using inhibition assays, western blotting and ELISAs.

Results

The results showed that pretreatment with GEVs enhanced with G. intestinalis (GEVs + G. intestinalis) induced IL-1β, IL-6 and TNF-α transcription and secretion from mouse macrophages compared to stimulation with either GEVs or G. intestinalis alone. Inoculation of mouse macrophages with GEVs upregulated the phosphorylation levels of the p38 MAPK, p44/42 MAPK (Erk1/2), AKT and NF-κB signaling pathways and led to the nuclear translocation of NF-κB p65. Blocking the activated p38, Erk and NF-κB signaling pathways significantly downregulated the secretion of proinflammatory cytokines, and blocking the activated AKT signaling pathway demonstrated reverse effects.

Conclusions

The results of this study reveal that GEVs can enhance G. intestinalis-induced inflammatory response levels in mouse macrophages through activation of the p38, ERK and NF-κB signaling pathways. The role of GEVs in regulating host cell immune responses may provide insights into exploring the underlying mechanisms in G. intestinalis–host interactions.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04865-5.

Extracellular vesicles and leishmaniasis: Current knowledge and promising avenues for future development

Extracellular vesicles (EVs) are small, membrane-bound "delivery trucks" that are present in the extracellular environment, including biological fluids. EVs are capable of inducing changes in the physiological status of neighboring cells through the transfer of key macromolecules, and are thought to play a role in a number of pathological processes. Leishmaniasis, caused by the protozoan parasite Leishmania, is an important example. The biology of Leishmania EVs has been studied in detail, and findings point to their role in exacerbation of disease and potential involvement in the perpetuation of drug resistance. Furthermore, the use of EVs for development of vaccines has been explored, as well as their potential use in a number of fields as biomarkers of disease and drug resistance. Here we discuss the latest findings on EVs, with a particular focus on Leishmania, as well as potential avenues for their future development and clinical applications.

The Leishmania donovani LDBPK_220120.1 Gene Encodes for an Atypical Dual Specificity Lipid-Like Phosphatase Expressed in Promastigotes and Amastigotes; Substrate Specificity, Intracellular Localizations, and Putative Role(s)

The intracellular protozoan parasites of the Leishmania genus are responsible for Leishmaniases, vector borne diseases with a wide range of clinical manifestations. Leishmania (L.) donovani causes visceral leishmaniasis (kala azar), the most severe of these diseases. Along their biological cycle, Leishmania parasites undergo distinct developmental transitions including metacyclogenesis and differentiation of metacyclic promastigotes (MPs) to amastigotes. Metacyclogenesis inside the phlebotomine sandfly host's midgut converts the procyclic dividing promastigotes to non-dividing infective MPs eventually injected into the skin of mammalian hosts and phagocytosed by macrophages where the MPs are converted inside modified phagolysosomes to the intracellular amastigotes. These developmental transitions involve dramatic changes in cell size and shape and reformatting of the flagellum requiring thus membrane and cytoskeleton remodeling in which phosphoinositide (PI) signaling and metabolism must play central roles. This study reports on the LDBPK_220120.1 gene, the L. donovani ortholog of LmjF.22.0250 from L. major that encodes a phosphatase from the "Atypical Lipid Phosphatases" (ALPs) enzyme family. We confirmed the expression of the LDBPK_220120.1 gene product in both L. donovani promastigotes and axenic amastigotes and showed that it behaves in vitro as a Dual Specificity P-Tyr and monophosphorylated [PI(3)P and PI(4)P] PI phosphatase and therefore named it LdTyrPIP_22 (Leishmaniad onovani Tyrosine PI Phosphatase, gene locus at chromosome 22). By immunofluorescence confocal microscopy we localized the LdTyrPIP_22 in several intracellular sites in the cell body of L. donovani promastigotes and amastigotes and in the flagellum. A temperature and pH shift from 25°C to 37°C and from pH 7 to 5.5, induced a pronounced recruitment of LdTyrPIP_22 epitopes to the flagellar pocket and a redistribution around the nucleus. These results suggest possible role(s) for this P-Tyr/PI phosphatase in the regulation of processes initiated or upregulated by this temperature/pH shift that contribute to the developmental transition from MPs to amastigotes inside the mammalian host macrophages.

The Benefits of Exporting: Engineered Extracellular Vesicles as Promising Vaccine Candidates against Enteric Fever

The immunological potential of extracellular vesicles produced by Gram-negative bacteria, the so-called outer-membrane vesicles (OMVs), can be improved by genetic engineering, resulting in vesicles containing multiple immunogens. The potential of this approach for the development of a vaccine candidate for enteric fever was recently demonstrated by G. Gasperini, R. Alfini, V. Arato, F. Mancini, et al. (Infect Immun 89:e00699-20, 2021, https://doi.org/10.1128/IAI.00699-20). This commentary will discuss the use of OMVs to generate vaccines for enteric fever and the promise of this approach for prevention of other infectious diseases.

The Role of Innate Immunity in Pulmonary Infections

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane-bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

Cross-Kingdom Extracellular Vesicles EV-RNA Communication as a Mechanism for Host-Pathogen Interaction

The extracellular vesicle (EVs) traffic has been highlighted as a very important pathway of cellular communication. EVs are produced by prokaryotes and eukaryotes organisms and can carry molecules to help maintain homeostasis, responding to general disbalance, infections, and allowing rapid modulation of the immune system. In the context of infection, EVs from both the host and the pathogen have been identified as playing roles in the recruitment of immunological molecules that can lead to the resolution of the infection or the host’s defeat. Bacterial vesicles RNA cargo play roles in the host cell by regulating gene expression and modulating immune response. In fungi the RNA molecules present in EVs are diverse and participate in communication between the host and pathogenic fungi. Little is known about how cross-kingdom sRNA trafficking occurs, although in recent years, there has been an increase in studies that relate EV participation in sRNA delivery. This review aims to elucidate and update the reader concerning the role of extracellular vesicles, with emphasis in the RNA content. We describe the EVs during infection from the host point-of-view, as well as the bacteria and fungi pathogens producing EVs that help the establishment of the disease.

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.

Leishmania-infected macrophages release extracellular vesicles that can promote lesion development

Macrophages infected with Leishmania donovani release extracellular vesicles that are composed of parasite and host-derived molecules that have the potential to induce vascular changes in tissues.

Leishmania donovani infection of macrophages results in quantitative and qualitative changes in the protein profile of extracellular vesicles (EVs) released by the infected host cells. We confirmed mass spectrometry results orthogonally by performing Western blots for several Leishmania-infected macrophage-enriched EVs (LieEVs) molecules. Several host cell proteins in LieEVs have been implicated in promoting vascular changes in other systems. We also identified 59 parasite-derived proteins in LieEVs, including a putative L. donovani homolog of mammalian vasohibins (LdVash), which in mammals promotes angiogenesis. We developed a transgenic parasite that expressed an endogenously tagged LdVash/mNeonGreen (mNG) and confirmed that LdVash/mNG is indeed expressed in infected macrophages and in LieEVs. We further observed that LieEVs induce endothelial cells to release angiogenesis promoting mediators including IL-8, G-CSF/CSF-3, and VEGF-A. In addition, LieEVs induce epithelial cell migration and tube formation by endothelial cells in surrogate angiogenesis assays. Taken together, these studies show that Leishmania infection alters the composition of EVs from infected cells and suggest that LieEVs may play a role in the promotion of vascularization of Leishmania infections.

Leishmania infection triggers hepcidin-mediated proteasomal degradation of Nramp1 to increase phagolysosomal iron availability

Natural resistance-associated macrophage protein 1 (Nramp1) was originally discovered as a genetic determinant of resistance against multiple intracellular pathogens, including Leishmania. It encodes a transmembrane protein of the phago-endosomal compartments, where it functions as an iron transporter. But the mechanism by which Nramp1 controls host-pathogen dynamics and determines final outcome of an infection is yet to be fully deciphered. Whether the expression of Nramp1 is altered in response to a pathogen attack is also unknown. To address these, Nramp1 status was examined in Leishmania major-infected murine macrophages. We observed that at 12 hrs post infection, there was drastic lowering of Nramp1 level accompanied by increased phagolysosomal iron content and enhanced intracellular parasite growth. Leishmania infection-induced Nramp1 downregulation was caused by ubiquitin-proteasome degradation pathway, which in turn was found to be mediated by the iron-regulatory peptide hormone hepcidin. Blocking of Nramp1 degradation with proteasome inhibitor or transcriptional agonist of hepcidin resulted in depletion of phagolysosomal iron pool that led to significant reduction of intracellular parasite burden. Interestingly, Nramp1 level was restored to normalcy after 30 hrs of infection with a concomitant drop in phagolysosomal iron, which is suggestive of a host counteractive response to deprive the pathogen of this essential micronutrient. Taken together, our study implicates Nramp1 as a central player in the host-pathogen battle for phagolysosomal iron. We also report Nramp1 as a novel target for hepcidin, and this 'hepcidin-Nramp1' axis may have a broader role in regulating macrophage iron homeostasis.

Perils and Promises of Pathogenic Protozoan Extracellular Vesicles

Extracellular vesicles (EVs) are membranous structures formed during biological processes in living organisms. For protozoan parasites, secretion of EVs can occur directly from the parasite organellar compartments and through parasite-infected or antigen-stimulated host cells in response to in vitro and in vivo physiological stressors. These secreted EVs characteristically reflect the biochemical features of their parasitic origin and activating stimuli. Here, we review the species-specific morphology and integrity of parasitic protozoan EVs in concurrence with the origin, functions, and internalization process by recipient cells. The activating stimuli for the secretion of EVs in pathogenic protozoa are discoursed alongside their biomolecules and specific immune cell responses to protozoan parasite-derived EVs. We also present some insights on the intricate functions of EVs in the context of protozoan parasitism.

Immunomodulatory Properties of Leishmania Extracellular Vesicles During Host-Parasite Interaction: Differential Activation of TLRs and NF-κB Translocation by Dermotropic and Viscerotropic Species

Leishmania infection causes considerable human morbidity and may develop into a deadly visceral form in endemic regions. The parasite infects macrophages where they can replicate intracellularly. Furthermore, they modulate host immune responses by using virulence factors (lipophosphoglycan, glycoprotein-63, and others) that promote survival inside the cells. Extracellular vesicles (EVs) released by parasites are important for cell-cell communication in the proinflammatory milieu modulating the establishment of infection. However, information on the ability of EVs from different Leishmania species to modulate inflammatory responses is scarce, especially from those species causing different clinical manifestations (visceral vs. cutaneous). The purpose of this study was to compare macrophage activation using EVs from three Leishmania species from New World including L. infantum, L. braziliensis, and L. amazonensis. EVs were released from promastigote forms, purified by ultracentrifugation and quantitated by Nanoparticle Tracking Analysis (NTA) prior to murine macrophage exposure. NTA analysis did not show any differences in the EV sizes among the strains. EVs from L. braziliensis and L. infantum failed to induce a pro-inflammatory response. EVs from both L. infantum WT and LPG-deficient mutant (LPG-KO) did not show any differences in their interaction with macrophages, suggesting that LPG solely was not determinant for activation. On the other hand, EVs from L. amazonensis were immunomodulatory inducing NO, TNF-α, IL-6, and IL-10 via TLR4 and TLR2. To determine whether such activation was related to NF-κB p65 translocation, THP-1 macrophage cells were exposed to EVs. In the same way, only EVs from L. amazonensis exhibited a highly percentage of cells positive for NF-κB. Our results suggest an important role of EVs in determining the pattern of immune response depending on the parasite species. For L. infantum, LPG was not determinant for the activation.

Unravelling the proteomic signature of extracellular vesicles released by drug-resistant Leishmania infantum parasites

Leishmaniasis constitutes the 9^th largest disease burden among all infectious diseases. Control of this disease is based on a short list of chemotherapeutic agents headed by pentavalent antimonials, followed by miltefosine and amphotericin B; drugs that are far from ideal due to host toxicity, elevated cost, limited access, and high rates of drug resistance. Knowing that the composition of extracellular vesicles (EVs) can vary according to the state of their parental cell, we hypothesized that EVs released by drug-resistant Leishmania infantum parasites could contain unique and differently enriched proteins depending on the drug-resistance mechanisms involved in the survival of their parental cell line. To assess this possibility, we studied EV production, size, morphology, and protein content of three well-characterized drug-resistant L. infantum cell lines and a wild-type strain. Our results are the first to demonstrate that drug-resistance mechanisms can induce changes in the morphology, size, and distribution of L. infantum EVs. In addition, we identified L. infantum’s core EV proteome. This proteome is highly conserved among strains, with the exception of a handful of proteins that are enriched differently depending on the drug responsible for induction of antimicrobial resistance. Furthermore, we obtained the first snapshot of proteins enriched in EVs released by antimony-, miltefosine- and amphotericin-resistant parasites. These include several virulence factors, transcription factors, as well as proteins encoded by drug-resistance genes. This detailed study of L. infantum EVs sheds new light on the potential roles of EVs in Leishmania biology, particularly with respect to the parasite’s survival in stressful conditions. This work outlines a crucial first step towards the discovery of EV-based profiles capable of predicting response to antileishmanial agents.

Visceral leishmaniasis is a life-threatening disease caused by Leishmania infantum parasites, which are transmitted by sand flies. In the absence of vaccines, current control of this disease is based on chemotherapy, which is comprised of a very limited arsenal threatened by the emergence and spread of drug-resistant strains. In the shadow of growing concern and treatment failure due to resistance, the characterization of extracellular vesicles (EVs) released by drug-resistant L. infantum parasites could shed some light on the complex nature of drug resistance in Leishmania and increase our understanding of the biology of the parasite. EVs are vesicles secreted by all eukaryotic cells whose contents (proteins, DNA/RNAs, lipids) vary as a function of their cellular origin. Our results demonstrate for the first time that EVs released by drug-resistant parasites are enriched in unique protein markers that reflect the drug-resistance mechanisms involved in the survival of parental cells. These unique proteins included several virulence and transcription factors, as well as drug-resistance genes; this offers a potential benefit for drug-resistant parasites in terms of parasite-to-parasite communication and host-parasite interactions. Collectively, our initial results could serve as a jumping-off point for the future development of novel EV-based diagnostic tools for the detection and appraisal of antimicrobial-resistant Leishmania populations.

Extracellular vesicles in infectious diseases caused by protozoan parasites in buffaloes

Background

Extracellular vesicles (EVs) are small membrane-bound vesicles of growing interest in vetetinary parasitology. The aim of the present report was to provide the first isolation, quantification and protein characterization of EVs from buffalo (Bubalus bubalis) sera infected with Theileria spp.

Methods

Infected animals were identified through optical microscopy and PCR. EVs were isolated from buffalo sera by size-exclusion chromatography and characterized using western blotting analysis, nanoparticle tracking analysis and transmission electron microscopy. Subsequently, the proteins from isolated vesicles were characterized by mass spectrometry.

Results

EVs from buffalo sera have shown sizes in the 124-140 nm range and 306 proteins were characterized. The protein-protein interaction analysis has evidenced biological processes and molecular function associated with signal transduction, binding, regulation of metabolic processes, transport, catalytic activity and response to acute stress. Five proteins have been shown to be differentially expressed between the control group and that infected with Theileria spp., all acting in the oxidative stress pathway.

Conclusions

EVs from buffaloes infected with Theileria spp. were successfully isolated and characterized. This is an advance in the knowledge of host-parasite relationship that contributes to the understanding of host immune response and theileriosis evasion mechanisms. These findings may pave the way for searching new EVs candidate-markers for a better production of safe biological products derived from buffaloes.

Touching the Surface: Diverse Roles for the Flagellar Membrane in Kinetoplastid Parasites

While flagella have been studied extensively as motility organelles, with a focus on internal structures such as the axoneme, more recent research has illuminated the roles of the flagellar surface in a variety of biological processes. Parasitic protists of the order Kinetoplastida, which include trypanosomes and Leishmania species, provide a paradigm for probing the role of flagella in host-microbe interactions and illustrate that this interface between the flagellar surface and the host is of paramount importance. An increasing body of knowledge indicates that the flagellar membrane serves a multitude of functions at this interface: attachment of parasites to tissues within insect vectors, close interactions with intracellular organelles of vertebrate cells, transactions between flagella from different parasites, junctions between the flagella and the parasite cell body, emergence of nanotubes and exosomes from the parasite directed to either host or microbial targets, immune evasion, and sensing of the extracellular milieu. Recent whole-organelle or genome-wide studies have begun to identify protein components of the flagellar surface that must mediate these diverse host-parasite interactions. The increasing corpus of knowledge on kinetoplastid flagella will likely prove illuminating for other flagellated or ciliated pathogens as well.