Dual role of the Leishmania major ribosomal protein S3a homologue in regulation of T- and B-cell activation

Immunomodulation by Leishmania parasites: Potential for controlling other diseases

In the mammalian hosts, Leishmania parasites survive and proliferate within phagolysosomes of macrophages. To avoid being killed by the immune cells, Leishmania parasites utilize their molecules to manipulate macrophages' functions for survival. Targets of such immunomodulatory molecules are not limited to macrophages, as Leishmania-derived molecules sometimes show influence on other immune cells such as neutrophils, dendritic cells, T cells and B cells. This review covers research on immunomodulation of host immunity by Leishmania parasites and introduces some examples of parasite-derived molecules participating in the immunomodulation. For example, Leishmania cell surface lipophosphoglycan (LPG) can modulate TLR2 signaling and PI3K/Akt axis in macrophages leading to induction of Th2 cells. Because chronic secretion of inflammatory cytokines is one of the causes of immune-mediated diseases such as atherosclerosis, Crohn's disease, and rheumatoid arthritis, LPG may be useful as a drug to suppress the inflammatory conditions. The unique characteristics of leishmanial molecules pose a promise as a source of immunomodulatory drugs for controlling diseases other than leishmaniasis.

Synthetic Peptides Selected by Immunoinformatics as Potential Tools for the Specific Diagnosis of Canine Visceral Leishmaniasis

Diagnosing canine visceral leishmaniasis (CVL) in Brazil faces challenges due to the limitations regarding the sensitivity and specificity of the current diagnostic protocol. Therefore, it is urgent to map new antigens or enhance the existing ones for future diagnostic techniques. Immunoinformatic tools are promising in the identification of new potential epitopes or antigen candidates. In this study, we evaluated peptides selected by epitope prediction for CVL serodiagnosis in ELISA assays. Ten B-cell epitopes were immunogenic in silico, but two peptides (peptides No. 45 and No. 48) showed the best performance in vitro. The selected peptides, both individually and in combination, were highly diagnostically accurate, with sensitivities ranging from 86.4% to 100% and with a specificity of approximately 90%. We observed that the combination of peptides showed better performance when compared to peptide alone, by detecting all asymptomatic dogs, showing lower cross-reactivity in sera from dogs with other canine infections, and did not detect vaccinated animals. Moreover, our data indicate the potential use of immunoinformatic tools associated with ELISA assays for the selection and evaluation of potential new targets, such as peptides, applied to the diagnosis of CVL.

Slc43a2+ T cell metastasis from spleen to brain in RGNNV infected teleost

The origin of T cells in the teleost's brain is unclear. While viewing the central nervous system (CNS) as immune privileged has been widely accepted, previous studies suggest that T cells residing in the thymus but not in the spleen of the teleost play an essential role in communicating with the peripheral organs. Here, we identified nine T cell subpopulations in the thymus and spleen of orange-spotted grouper (Epinephelus coioices) through single-cell RNA-sequencing analysis. After viral CNS infection with red-spotted grouper nervous necrosis virus (RGNNV), the number of slc43a2+ T cells synchronously increased in the spleen and brain. During the infection tests in asplenic zebrafish (tlx1▲ zebrafish model), no increase in the number of slc43a2+ T cells was observed in the brain. Single-cell transcriptomic analysis indicated that slc43a2+ T cells mature and functionally differentiate within the spleen and then migrate into the brain to trigger an immune response. This study suggests a novel route for T cell migration from the spleen to the brain during viral infection in fish.

Recent Advances in Tick Antigen Discovery and Anti-Tick Vaccine Development

Ticks can seriously affect human and animal health around the globe, causing significant economic losses each year. Chemical acaricides are widely used to control ticks, which negatively impact the environment and result in the emergence of acaricide-resistant tick populations. A vaccine is considered as one of the best alternative approaches to control ticks and tick-borne diseases, as it is less expensive and more effective than chemical controls. Many antigen-based vaccines have been developed as a result of current advances in transcriptomics, genomics, and proteomic techniques. A few of these (e.g., Gavac® and TickGARD®) are commercially available and are commonly used in different countries. Furthermore, a significant number of novel antigens are being investigated with the perspective of developing new anti-tick vaccines. However, more research is required to develop new and more efficient antigen-based vaccines, including on assessing the efficiency of various epitopes against different tick species to confirm their cross-reactivity and their high immunogenicity. In this review, we discuss the recent advancements in the development of antigen-based vaccines (traditional and RNA-based) and provide a brief overview of recent discoveries of novel antigens, along with their sources, characteristics, and the methods used to test their efficiency.

In silico analysis of Leishmania proteomes and protein-protein interaction network: Prioritizing therapeutic targets and drugs for repurposing to treat leishmaniasis

Leishmaniasis is a serious world health problem and its current therapies have several limitations demanding to develop novel therapeutics for this disease. The present study aims to prioritize novel broad-spectrum targets using proteomics and protein-protein interaction network (PPIN) data for 11 Leishmania species. Proteome comparison and host non-homology analysis resulted in 3605 pathogen-specific conserved core proteins. Gene ontology analysis indicated their involvement in major molecular functions like DNA binding, transportation, dioxygenase, and catalytic activity. PPIN analysis of these core proteins identified eight hub proteins (viz., vesicle-trafficking protein (LBRM2903_190011800), ribosomal proteins S17 (LBRM2903_34004790) and L2 (LBRM2903_080008100), eukaryotic translation initiation factor 3 (LBRM2903_350086700), replication factor A (LBRM2903_150008000), U3 small nucleolar RNA-associated protein (LBRM2903_340025600), exonuclease (LBRM2903_200021800), and mitochondrial RNA ligase (LBRM2903_200074100)). Among the hub proteins, six were classified as drug targets and two as vaccine candidates. Further, druggability analysis indicated three hub proteins, namely eukaryotic translation initiation factor 3, ribosomal proteins S17 and L2 as druggable. Their three-dimensional structures were modelled and docked with the identified ligands (2-methylthio-N6-isopentenyl-adenosine-5'-monophosphate, artenimol and omacetaxine mepesuccinate). These ligands could be experimentally validated (in vitro and in vivo) and repurposed for the development of novel antileishmanial agents.

Utilizing Quantitative Proteomics to Identify Species-Specific Protein Therapeutic Targets for the Treatment of Leishmaniasis

Leishmaniasis is a tropical disease caused by Leishmania parasites, which are transmitted through the bites of infected sandflies. We focused on the emergence of leishmaniasis in Thailand caused by a species (Leishmania orientalis). Treatment by chemotherapy is not effective against L. orientalis. Hence, we intended to solve this issue using a proteomics approach to investigate protein profiles and in silico analysis for the identification of antigenic proteins from L. orientalis, Leishmania martiniquensis, and Leishmania donovani. Using principal component analysis (PCA), protein profile comparisons indicated that different species of Leishmania are different at the protein level. Proteomics analysis identified 6099 proteins. Among these proteins, 1065 proteins were used for further analysis. There were 16 proteins that were promising candidates for therapeutic aspects as they were abundantly expressed and common to all species. In silico analysis of protein's antigenicity revealed that eight proteins had the potential for the development of antigenic molecules. Protein profile information and these antigenic proteins may play key roles in the pathogeny of leishmaniasis and can be used as novel therapeutic targets against leishmaniasis in the future.

Characterization of Differentially Abundant Proteins Among Leishmania (Viannia) braziliensis Strains Isolated From Atypical or Typical Lesions

Leishmania (Viannia) braziliensis is the main etiological agent of cutaneous and mucocutaneous leishmaniasis in Latin America. Non-ulcerated atypical tegumentary leishmaniasis cases caused by L. braziliensis have been reported in several regions of the American continent, including the Xacriabá indigenous reserve in São João das Missões/Minas Gerais, Brazil. Parasites isolated from these atypical clinical lesions are resistant to antimony-based therapeutics. In the present study, proteins displaying differential abundance in two strains of L. braziliensis isolated from patients with atypical lesions compared with four strains isolated from patients with typical lesions were identified using a quantitative proteomics approach based on tandem mass tag labeling (TMT) and mass spectrometry. A total of 532 (P<0.05) differentially abundant proteins were identified (298 upregulated and 234 downregulated) in strains from atypical lesions compared to strains from typical lesions. Prominent positively regulated proteins in atypical strains included those that may confer greater survival inside macrophages, proteins related to antimony resistance, and proteins associated with higher peroxidase activity. Additionally, we identified proteins showing potential as new drug and vaccine targets. Our findings contribute to the characterization of these intriguing L. braziliensis strains and provide a novel perspective on Atypical Cutaneous Leishmaniasis (ACL) cases that have been associated with therapeutic failures.

In Leishmania major, the Homolog of the Oncogene PES1 May Play a Critical Role in Parasite Infectivity

Leishmaniasis is a neglected tropical disease caused by Leishmania spp. The improvement of existing treatments and the discovery of new drugs remain ones of the major goals in control and eradication of this disease. From the parasite genome, we have identified the homologue of the human oncogene PES1 in Leishmania major (LmjPES). It has been demonstrated that PES1 is involved in several processes such as ribosome biogenesis, cell proliferation and genetic transcription. Our phylogenetic studies showed that LmjPES encodes a highly conserved protein containing three main domains: PES N-terminus (shared with proteins involved in ribosomal biogenesis), BRCT (found in proteins related to DNA repair processes) and MAEBL-type domain (C-terminus, related to erythrocyte invasion in apicomplexan). This gene showed its highest expression level in metacyclic promastigotes, the infective forms; by fluorescence microscopy assay, we demonstrated the nuclear localization of LmjPES protein. After generating mutant parasites overexpressing LmjPES, we observed that these clones displayed a dramatic increase in the ratio of cell infection within macrophages. Furthermore, BALB/c mice infected with these transgenic parasites exhibited higher footpad inflammation compared to those inoculated with non-overexpressing parasites.

Rhipicephalus microplus: An overview of vaccine antigens against the cattle tick

Rhipicephalus microplus, popularly known as the cattle tick, is the most important tick of livestock as it is responsible for significant economic losses. The use of chemical acaricides is still the most widely used control method despite its known disadvantages. Vaccination would be a safe alternative for the control of R. microplus and holds advantages over the use of chemical acaricides as it is environmental-friendly and leaves no residues in meat or milk. Two vaccines based on the Bm86 protein were commercialized, TickGARD® and Gavac®, with varying reported efficacies in different countries. The use of other vaccines, such as Tick Vac®, Go-Tick®, and Bovimune Ixovac® have been restricted to some countries. Several other proteins have been analyzed as possible antigens for more effective vaccines against R. microplus, including peptidases, serine proteinase inhibitors, glutathione S-transferases, metalloproteases, and ribosomal proteins, with efficacies ranging from 14% to 96%. Nonetheless, more research is needed to develop safe and efficient tick vaccines, such as the evaluation of the efficacy of antigens against other tick species to verify cross-reactivity and inclusion of additional antigens to promote the blocking of the infection and spreading of tick-borne diseases. This review summarizes the discoveries of candidate antigens for R. microplus tick vaccines as well as the methods used to test their efficacy.

The role of epigenetic mechanisms in the regulation of gene expression in the cyclical endometrium

BACKGROUND

The human endometrium is a highly dynamic tissue whose function is mainly regulated by the ovarian steroid hormones estradiol and progesterone. The serum levels of these and other hormones are associated with three specific phases that compose the endometrial cycle: menstrual, proliferative, and secretory. Throughout this cycle, the endometrium exhibits different transcriptional networks according to the genes expressed in each phase. Epigenetic mechanisms are crucial in the fine-tuning of gene expression to generate such transcriptional networks. The present review aims to provide an overview of current research focused on the epigenetic mechanisms that regulate gene expression in the cyclical endometrium and discuss the technical and clinical perspectives regarding this topic.

MAIN BODY

The main epigenetic mechanisms reported are DNA methylation, histone post-translational modifications, and non-coding RNAs. These epigenetic mechanisms induce the expression of genes associated with transcriptional regulation, endometrial epithelial growth, angiogenesis, and stromal cell proliferation during the proliferative phase. During the secretory phase, epigenetic mechanisms promote the expression of genes associated with hormone response, insulin signaling, decidualization, and embryo implantation. Furthermore, the global content of specific epigenetic modifications and the gene expression of non-coding RNAs and epigenetic modifiers vary according to the menstrual cycle phase. In vitro and cell type-specific studies have demonstrated that epithelial and stromal cells undergo particular epigenetic changes that modulate their transcriptional networks to accomplish their function during decidualization and implantation.

CONCLUSION AND PERSPECTIVES

Epigenetic mechanisms are emerging as key players in regulating transcriptional networks associated with key processes and functions of the cyclical endometrium. Further studies using next-generation sequencing and single-cell technology are warranted to explore the role of other epigenetic mechanisms in each cell type that composes the endometrium throughout the menstrual cycle. The application of this knowledge will definitively provide essential information to understand the pathological mechanisms of endometrial diseases, such as endometriosis and endometrial cancer, and to identify potential therapeutic targets and improve women's health.

HLA-DRB1 Alleles Associated with Lower Leishmaniasis Susceptibility Share Common Amino Acid Polymorphisms and Epitope Binding Repertoires

Susceptibility for leishmaniasis is largely dependent on host genetic and immune factors. Despite the previously described association of human leukocyte antigen (HLA) gene cluster variants as genetic susceptibility factors for leishmaniasis, little is known regarding the mechanisms that underpin these associations. To better understand this underlying functionality, we first collected all known leishmaniasis-associated HLA variants in a thorough literature review. Next, we aligned and compared the protection- and risk-associated HLA-DRB1 allele sequences. This identified several amino acid polymorphisms that distinguish protection- from risk-associated HLA-DRB1 alleles. Subsequently, T cell epitope binding predictions were carried out across these alleles to map the impact of these polymorphisms on the epitope binding repertoires. For these predictions, we used epitopes derived from entire proteomes of multiple Leishmania species. Epitopes binding to protection-associated HLA-DRB1 alleles shared common binding core motifs, mapping to the identified HLA-DRB1 amino acid polymorphisms. These results strongly suggest that HLA polymorphism, resulting in differential antigen presentation, affects the association between HLA and leishmaniasis disease development. Finally, we established a valuable open-access resource of putative epitopes. A set of 14 HLA-unrestricted strong-binding epitopes, conserved across species, was prioritized for further epitope discovery in the search for novel subunit-based vaccines.

Proteomic analysis reveals differentially abundant proteins probably involved in the virulence of amastigote and promastigote forms of Leishmania infantum

Owing to the importance and clinical diversity of Leishmania infantum, studying its virulence factors is promising for understanding the relationship between parasites and hosts. In the present study, differentially abundant proteins from strains with different degrees of virulence in promastigote and amastigote forms were compared using two quantitative proteomics techniques, differential gel electrophoresis and isobaric mass tag labeling, followed by identification by mass spectrometry. A total of 142 proteins were identified: 96 upregulated and 46 downregulated proteins in the most virulent strain compared to less virulent. The interaction between the proteins identified in each evolutionary form was predicted. The results showed that in the amastigote form of the most virulent strain, there was a large group of proteins related to glycolysis, heat shock, and ribosomal proteins, whereas in the promastigote form, the group consisted of stress response, heat shock, and ribosomal proteins. In addition, biological processes related to metabolic pathways, ribosomes, and oxidative phosphorylation were enriched in the most virulent strain (BH400). Finally, we noted several proteins previously found to play important roles in L. infantum infection, which showed increased abundance in the virulent strain, such as ribosomal proteins, HSP70, enolase, fructose 1,6-biphosphate aldolase, peroxidoxin, and tryparedoxin peroxidase, many of which interact with each other.

CYTED Network to develop an immunogen compatible with integrated management strategies for tick control in cattle

INCOGARR is a thematic network recently approved to be financially supported by the Ibero-American Program of Science and Technology for Development (CYTED). The objectives of this Network are the design and evaluation of an efficient and feasible anti-tick vaccine candidate from the technical and economical points of view and also sharing experiences in the immunological control of ticks as part of an Integrated Control Program. The Network consists of seven laboratories and one company from six countries. The first meeting of the Network took place with the representation of each laboratory involved. In the meeting, general and specific objectives and activities of the Network were discussed and it was a very nice example of international collaboration to address an unsolved worldwide topic on tick control in which laboratories with different competencies and expertise join their efforts in a common goal.

Reduced pathogenicity of fructose-1,6-bisphosphatase deficient Leishmania donovani and its use as an attenuated strain to induce protective immunogenicity

Currently, there is no approved vaccine for visceral leishmaniasis (VL) caused by L. donovani. The ability to manipulate Leishmania genome by eliminating or introducing genes necessary for parasites' survival considered as the powerful strategy to generate the live attenuated vaccine. In the present study fructose-1,6-bisphosphatase (LdFBPase) gene deleted L. donovani (Δfbpase) was generated using homologous gene replacement strategy. Though LdFBPase gene deletion (Δfbpase) does not affect the growth of parasite in the promastigote form but axenic amastigotes display a marked reduction in their capacity to multiply in vitro inside macrophages and in vivo in Balb/c mice. Though Δfbpase L. donovani parasite persisted in BALB/c mice up to 12 weeks but was unable to cause infection, we tested its ability to protect against a virulent L. donovani challenge. Notably, intraperitoneal immunisation with live Δfbpase parasites displayed the reduction of parasites load in mice spleen and liver post challenge. Moreover, immunised BALB/c mice showed a reversal of T cell anergy and high levels of NO production that result in the killing of the parasite. A significant, correlation was found between parasite clearance and elevated IFNγ, IL12, and IFNγ/IL10 ratio compared to IL10 and TGFβ in immunised and challenged mice. Results suggested the generation of protective Th1 type immune response which induced significant parasite clearance at 12-week, as well as 16 weeks post, challenged immunised mice, signifying sustained immunity. Therefore, we propose that Δfbpase L. donovani parasites can be a live attenuated vaccine candidate for VL and a good model to understand the correlatives of protection in visceral leishmaniasis.

Analysis of the Antigenic and Prophylactic Properties of the Leishmania Translation Initiation Factors eIF2 and eIF2B in Natural and Experimental Leishmaniasis

Different members of intracellular protein families are recognized by the immune system of the vertebrate host infected by parasites of the genus Leishmania. Here, we have analyzed the antigenic and immunogenic properties of the Leishmania eIF2 and eIF2B translation initiation factors. An in silico search in Leishmania infantum sequence databases allowed the identification of the genes encoding the α, β, and γ subunits and the α, β, and δ subunits of the putative Leishmania orthologs of the eukaryotic initiation factors F2 (LieIF2) or F2B (LieIF2B), respectively. The antigenicity of these factors was analyzed by ELISA using recombinant versions of the different subunits. Antibodies against the different LieIF2 and LieIF2B subunits were found in the sera from human and canine visceral leishmaniasis patients, and also in the sera from hamsters experimentally infected with L. infantum. In L. infantum (BALB/c) and Leishmania major (BALB/c or C57BL/6) challenged mice, a moderate humoral response against these protein factors was detected. Remarkably, these proteins elicited an IL-10 production by splenocytes derived from infected mice independently of the Leishmania species employed for experimental challenge. When DNA vaccines based on the expression of the LieIF2 or LieIF2B subunit encoding genes were administered in mice, an antigen-specific secretion of IFN-γ and IL-10 cytokines was observed. Furthermore, a partial protection against murine CL development due to L. major infection was generated in the vaccinated mice. Also, in this work we show that the LieIF2α subunit and the LieIF2Bβ and δ subunits have the capacity to stimulate IL-10 secretion by spleen cells from naïve mice. B-lymphocytes were identified as the major producers of this anti-inflammatory cytokine. Taking into account the data found in this study, it may be hypothesized that these proteins act as virulence factors implicated in the induction of humoral responses as well as in the production of the down-regulatory IL-10 cytokine, favoring a pathological outcome. Therefore, these proteins might be considered markers of disease.

The Deadly Dance of B Cells with Trypanosomatids

B cells are notorious actors for the host's protection against several infectious diseases. So much so that early vaccinology seated its principles upon their long-term protective antibody secretion capabilities. Indeed, there are many examples of acute infectious diseases that are combated by functional humoral responses. However, some chronic infectious diseases actively induce immune deregulations that often lead to defective, if not deleterious, humoral immune responses. In this review we summarize how Leishmania and Trypanosoma spp. directly manipulate B cell responses to induce polyclonal B cell activation, hypergammaglobulinemia, low-specificity antibodies, limited B cell survival, and regulatory B cells, contributing therefore to immunopathology and the establishment of persistent infections.

Immunoinformatics Features Linked to Leishmania Vaccine Development: Data Integration of Experimental and In Silico Studies

Leishmaniasis is a wide-spectrum disease caused by parasites from Leishmania genus. There is no human vaccine available and it is considered by many studies as apotential effective tool for disease control. To discover novel antigens, computational programs have been used in reverse vaccinology strategies. In this work, we developed a validation antigen approach that integrates prediction of B and T cell epitopes, analysis of Protein-Protein Interaction (PPI) networks and metabolic pathways. We selected twenty candidate proteins from Leishmania tested in murine model, with experimental outcome published in the literature. The predictions for CD4⁺ and CD8⁺ T cell epitopes were correlated with protection in experimental outcomes. We also mapped immunogenic proteins on PPI networks in order to find Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with them. Our results suggest that non-protective antigens have lowest frequency of predicted T CD4⁺ and T CD8⁺ epitopes, compared with protective ones. T CD4⁺ and T CD8⁺ cells are more related to leishmaniasis protection in experimental outcomes than B cell predicted epitopes. Considering KEGG analysis, the proteins considered protective are connected to nodes with few pathways, including those associated with ribosome biosynthesis and purine metabolism.

Coadministration of the Three Antigenic Leishmania infantum Poly (A) Binding Proteins as a DNA Vaccine Induces Protection against Leishmania major Infection in BALB/c Mice

BACKGROUND

Highly conserved intracellular proteins from Leishmania have been described as antigens in natural and experimental infected mammals. The present study aimed to evaluate the antigenicity and prophylactic properties of the Leishmania infantum Poly (A) binding proteins (LiPABPs).

METHODOLOGY/PRINCIPAL FINDINGS

Three different members of the LiPABP family have been described. Recombinant tools based on these proteins were constructed: recombinant proteins and DNA vaccines. The three recombinant proteins were employed for coating ELISA plates. Sera from human and canine patients of visceral leishmaniasis and human patients of mucosal leishmaniasis recognized the three LiPABPs. In addition, the protective efficacy of a DNA vaccine based on the combination of the three Leishmania PABPs has been tested in a model of progressive murine leishmaniasis: BALB/c mice infected with Leishmania major. The induction of a Th1-like response against the LiPABP family by genetic vaccination was able to down-regulate the IL-10 predominant responses elicited by parasite LiPABPs after infection in this murine model. This modulation resulted in a partial protection against L. major infection. LiPABP vaccinated mice showed a reduction on the pathology that was accompanied by a decrease in parasite burdens, in antibody titers against Leishmania antigens and in the IL-4 and IL-10 parasite-specific mediated responses in comparison to control mice groups immunized with saline or with the non-recombinant plasmid.

CONCLUSION/SIGNIFICANCE

The results presented here demonstrate for the first time the prophylactic properties of a new family of Leishmania antigenic intracellular proteins, the LiPABPs. The redirection of the immune response elicited against the LiPABP family (from IL-10 towards IFN-γ mediated responses) by genetic vaccination was able to induce a partial protection against the development of the disease in a highly susceptible murine model of leishmaniasis.

High efficacy of a 20 amino acid peptide of the acidic ribosomal protein P0 against the cattle tick, Rhipicephalus microplus

Current strategies to control cattle ticks use integrated control programs (ICP) that include vaccination. Reduction in the use of chemicals and in the cost of tick control, the delay or elimination of acaricide resistance and the decreasing of environmental pollution are the advantages of using these programs. This integrated program is potentially applicable to all genotypes of chemical resistant ticks. However, the problem here is to improve the efficacy of anti-tick vaccines. The P0 protein is a structural component of the ribosome of all organisms. We have identified an immunogenic region of ribosomal protein P0 from Rhipicephalus spp. ticks that is not very conserved compared to the orthologous protein in their hosts. A synthetic 20 amino acid peptide from this sequence was effective as a vaccine against Rhipicephalus sanguineus infestations in an immunization and challenge experiment using rabbits. In this paper, the same peptide used as vaccine against the cattle tick Rhipicephalus Boophilus microplus shows a significant diminution in the number of engorged females recovered, in the weight of females and the weight of egg masses. The number of eggs hatched was also significantly reduced for the vaccinated group, with an overall effectivity for the antigen pP0 of 96%. These results, together with the conserved sequence of the P0 peptide among ticks, suggest that this antigen could be a good broad spectrum vaccine candidate. It would be expected to be active against many species of ticks and thus has promise in an ICP for effective control of ticks and thereby to improve the efficiency and productivity of the livestock industry.

Deception and manipulation: the arms of leishmania, a successful parasite

Leishmania spp. are intracellular parasitic protozoa responsible for a group of neglected tropical diseases, endemic in 98 countries around the world, called leishmaniasis. These parasites have a complex digenetic life cycle requiring a susceptible vertebrate host and a permissive insect vector, which allow their transmission. The clinical manifestations associated with leishmaniasis depend on complex interactions between the parasite and the host immune system. Consequently, leishmaniasis can be manifested as a self-healing cutaneous affliction or a visceral pathology, being the last one fatal in 85–90% of untreated cases. As a result of a long host–parasite co-evolutionary process, Leishmania spp. developed different immunomodulatory strategies that are essential for the establishment of infection. Only through deception and manipulation of the immune system, Leishmania spp. can complete its life cycle and survive. The understanding of the mechanisms associated with immune evasion and disease progression is essential for the development of novel therapies and vaccine approaches. Here, we revise how the parasite manipulates cell death and immune responses to survive and thrive in the shadow of the immune system.

Ultrastructural study on tissue alterations caused by trypanosomatids in experimental murine infections

The ultrastructural study in different tissues of mice experimentally infected with isolates of Trypanosoma evansi, Trypanosoma cruzi, and Leishmania mexicana reveals changes in cardiac myocytes, skeletal muscle fibers, and hepatic, adrenal, kidney, and spleen cells. Some of these changes were cytoarchitectural and others consisted of necrosis. Alterations in the microvasculature were also found. The mononuclear cell infiltrate included neutrophils, eosinophils, and macrophages. This work shows that diverse mice tissues are important target for trypanosomatids.

A 24-48 h fed Amblyomma americanum tick saliva immuno-proteome

BACKGROUND

Multiple tick saliva proteins, the majority of which are unknown, confer tick resistance in repeatedly infested animals. The objective of this study was to identify the 24-48 h fed Amblyomma americanum tick saliva immuno-proteome. The 24-48 h tick-feeding phase is critical to tick parasitism as it precedes important events in tick biology, blood meal feeding and disease agent transmission. Fed male, 24 and 96 h fed female phage display cDNA expression libraries were biopanned using rabbit antibodies to 24 and 48 h fed A. americanum female tick saliva proteins. Biopanned immuno-cDNA libraries were subjected to next generation sequencing, de novo assembly, and bioinformatic analysis.

RESULTS

More than 800 transcripts that code for 24-48 h fed A. americanum immuno-proteins are described. Of the 895 immuno-proteins, 52% (464/895) were provisionally identified based on matches in GenBank. Of these, ~19% (86/464) show high level of identity to other tick hypothetical proteins, and the rest include putative proteases (serine, cysteine, leukotriene A-4 hydrolase, carboxypeptidases, and metalloproteases), protease inhibitors (serine and cysteine protease inhibitors, tick carboxypeptidase inhibitor), and transporters and/or ligand binding proteins (histamine binding/lipocalin, fatty acid binding, calreticulin, hemelipoprotein, IgG binding protein, ferritin, insulin-like growth factor binding proteins, and evasin). Others include enzymes (glutathione transferase, cytochrome oxidase, protein disulfide isomerase), ribosomal proteins, and those of miscellaneous functions (histamine release factor, selenoproteins, tetraspanin, defensin, heat shock proteins).

CONCLUSIONS

Data here demonstrate that A. americanum secretes a complex cocktail of immunogenic tick saliva proteins during the first 24-48 h of feeding. Of significance, previously validated immunogenic tick saliva proteins including AV422 protein, calreticulin, histamine release factor, histamine binding/lipocalins, selenoproteins, and paramyosin were identified in this screen, supporting the specificity of the approach in this study. While descriptive, this study opens opportunities for in-depth tick feeding physiology studies.

Abortive T follicular helper development is associated with a defective humoral response in Leishmania infantum-infected macaques

Leishmania infantum causes a chronic infectious disease named visceral leishmaniasis (VL). We employed a non-human primate model to monitor immune parameters over time and gain new insights into the disease. Rhesus macaques were infected with L. infantum and the T helper and B cell immunological profiles characterized during acute and chronic phases of infection. Parasite detection in visceral compartments during the acute phase was associated with differentiation of effector memory CD4 T cells and increased levels of Th1 transcripts. At the chronic phase, parasites colonized novel lymphoid niches concomitant with increased expression of IL10. Despite the occurrence of hypergammaglobulinemia, the production of parasite-specific IgG was poor, being confined to the acute phase and positively correlated with the frequency of an activated memory splenic B cell population. We noticed the expansion of a splenic CD4 T cell population expressing CXCR5 and Bcl-6 during acute infection that was associated with the differentiation of the activated memory B cell population. Moreover, the number of splenic germinal centers peaked at one month after infection, hence paralleling the production of specific IgG. However, at chronic infection these populations contracted impacting the production of parasite-specific IgG. Our study provides new insights into the immune events taking place in a physiologically relevant host and a mechanistic basis for the inefficient humoral response during VL.

Regulatory cells and immunosuppressive cytokines: parasite-derived factors induce immune polarization

Parasitic infections are prevalent in both tropical and subtropical areas. Most of the affected and/or exposed populations are living in developing countries where control measures are lacking or inadequately applied. Although significant progress has been made in our understanding of the immune response to parasites, no definitive step has yet been successfully done in terms of operational vaccines against parasitic diseases. Evidence accumulated during the past few years suggests that the pathology observed during parasitic infections is in part due to deregulation of normal components of the immune system, mainly cytokines, antibodies, and immune effector cell populations. A large number of studies that illustrate how parasites can modify the host immune system for their own benefit have been reported in both metazoan and protozoan parasites. The first line of defense against foreign organisms is barrier tissue such as skin, humoral factors, for instance the complement system and pentraxin, which upon activation of the complement cascade facilitate pathogen recognition by cells of innate immunity such as macrophages and DC. However, all the major groups of parasites studied have been shown to contain and/or to release factors, which interfere with both arms of the host immune system. Even some astonishing observations relate to the production by some parasites of orthologues of mammalian cytokines. Furthermore, chronic parasitic infections have led to the immunosuppressive environment that correlates with increased levels of myeloid and T suppressor cells that may limit the success of immunotherapeutic strategies based on vaccination. This minireview briefly analyzes some of the current data related to the regulatory cells and molecules derived from parasites that affect cellular function and contribute to the polarization of the immune response of the host. Special attention is given to some of the data from our laboratory illustrating the role of immunomodulatory factors released by protozoan parasites, in the induction and perpetuation of chronic disease.

Immune response regulation by leishmania secreted and nonsecreted antigens

Leishmania infection consists in two sequential events, the host cell colonization followed by the proliferation/dissemination of the parasite. In this review, we discuss the importance of two distinct sets of molecules, the secreted and/or surface and the nonsecreted antigens. The importance of the immune response against secreted and surface antigens is noted in the establishment of the infection and we dissect the contribution of the nonsecreted antigens in the immunopathology associated with leishmaniasis, showing the importance of these panantigens during the course of the infection. As a further example of proteins belonging to these two different groups, we include several laboratorial observations on Leishmania Sir2 and LicTXNPx as excreted/secreted proteins and LmS3arp and LimTXNPx as nonsecreted/panantigens. The role of these two groups of antigens in the immune response observed during the infection is discussed.

Vaccination with the Leishmania infantum ribosomal proteins induces protection in BALB/c mice against Leishmania chagasi and Leishmania amazonensis challenge

Leishmania chagasi and Leishmania amazonensis are the etiologic agents of different clinical forms of human leishmaniasis in South America. In an attempt to select candidate antigens for a vaccine protecting against different Leishmania species, the efficacy of vaccination using Leishmania ribosomal proteins and saponin as adjuvant was examined in BALB/c mice against challenge infection with both parasite species. Mice vaccinated with parasite ribosomal proteins purified from Leishmania infantum plus saponin showed a specific production of IFN-γ, IL-12 and GM-CSF after in vitro stimulation with L. infantum ribosomal proteins. Vaccinated mice showed a reduction in the liver and spleen parasite burdens after L. chagasi infection. After L. amazonensis challenge, vaccinated mice showed a decrease of the dermal pathology and a reduction in the parasite loads in the footpad and spleen. In both models, protection was correlated to an IL-12-dependent production of IFN-γ by CD4(+) and CD8(+) T cells that activate macrophages for the synthesis of NO. In the protected mice a decrease in the parasite-mediated IL-4 and IL-10 responses was also observed. In mice challenged with L. amazonensis, lower levels of anti-parasite-specific antibodies were detected. Thus, Leishmania ribosomal proteins plus saponin fits the requirements to compose a pan-Leishmania vaccine.

SIR2-deficient Leishmania infantum induces a defined IFN-gamma/IL-10 pattern that correlates with protection

The ability to manipulate the Leishmania genome to create genetically modified parasites by introducing or eliminating genes is considered a powerful alternative for developing a new generation vaccine against leishmaniasis. Previously, we showed that the deletion of one allele of the Leishmania infantum silent information regulatory 2 (LiSIR2) locus was sufficient to dramatically affect amastigote axenic proliferation. Furthermore, LiSIR2 single knockout (LiSIR2(+/-)) amastigotes were unable to replicate in vitro inside macrophages. Because this L. infantum mutant persisted in BALB/c mice for up to 6 wk but failed to establish an infection, we tested its ability to provide protection toward a virulent L. infantum challenge. Strikingly, vaccination with a single i.p. injection of LiSIR2(+/-) single knockout elicits complete protection. Thus, vaccinated BALB/c mice showed a reversal of T cell anergy with specific anti-Leishmania cytotoxic activity and high levels of NO production. Moreover, vaccinated mice simultaneously generated specific anti-Leishmania IgG Ab subclasses suggestive of both type 1 and type 2 responses. A strong correlation was found between the elimination of the parasites and an increased Leishmania-specific IFN-gamma/IL-10 ratio. Therefore, we propose that the polarization to a high IFN-gamma/low IL-10 ratio after challenge is a clear indicator of vaccine success. Furthermore these mutants, which presented attenuated virulence, represent a good model to understand the correlatives of protection in visceral leishmaniasis.

A Leishmania infantum cytosolic tryparedoxin activates B cells to secrete interleukin-10 and specific immunoglobulin

The immune evasion mechanisms of pathogenic trypanosomatids involve a multitude of phenomena such as the polyclonal activation of lymphocytes, cytokine modulation and the enhanced detoxification of oxygen reactive species. A trypanothione cascade seems to be involved in the detoxification process. It was recently described and characterized a tryparedoxin (LiTXN1) involved in Leishmania infantum cytoplasmatic hydroperoxide metabolism. LiTXN1 is a secreted protein that is up-regulated in the infectious form of the parasite, suggesting that it may play an important role during infection. In the present study, we investigated whether recombinant LiTXN1 (rLiTXN1) affects T- and B-cell functions in a murine model. We observed a significant increase in the CD69 surface marker on the B-cell population in total spleen cells and on isolated B cells from BALB/c mice after in vitro rLiTXN1 stimulus. Activated B-cells underwent further proliferation, as indicated by increased [(3)H]thymidine incorporation. Cytokine quantification showed a dose-dependent up-regulation of interleukin (IL)-10 secretion. B cells were identified as a source of this secretion. Furthermore, intraperitoneal injection of rLiTXN1 into BALB/c mice triggered the production of elevated levels of rLiTXN1-specific antibodies, predominantly of the immunoglobulin M (IgM), IgG1 and IgG3 isotypes, with a minimum reactivity against other heterologous antigens. Taken together, our data suggest that rLiTXN1 may participate in immunopathological processes by targeting B-cell effector functions, leading to IL-10 secretion and production of specific antibodies.

Polyclonal B cell activation in infections: infectious agents' devilry or defense mechanism of the host?

Polyclonal B cell activation is not a peculiar characteristic to a particular infection, as many viruses, bacteria, and parasites induce a strong polyclonal B cell response resulting in hyper-gamma-globulinemia. Here, we discuss the different roles proposed for polyclonal B cell activation, which can be crucial for early host defense against rapidly dividing microorganisms by contributing antibodies specific for a spectrum of conserved structures present in the pathogens. In addition, polyclonal B cell activation can be responsible for maintenance of memory B cell responses because of the continuous, unrestricted stimulation of memory B cells whose antibody production may be sustained in the absence of the antigens binding-specific BCR. Conversely, polyclonal activation can be triggered by microorganisms to avoid the host-specific, immune response by activating B cell clones, which produce nonmicroorganism-specific antibodies. Finally, some reports suggest a deleterious role for polyclonal activation, arguing that it could potentially turn on anti-self-responses and lead to autoimmune manifestations during chronic infections.

Leishmania cytosolic silent information regulatory protein 2 deacetylase induces murine B-cell differentiation and in vivo production of specific antibodies

In previous studies, we identified a gene product belonging to the silent information regulatory 2 protein (SIR2) family. This protein is expressed by all Leishmania species so far examined (L. major, L. infantum, L. amazonensis, L. mexicana) and found to be crucial for parasite survival and virulence. In the present study, we investigated whether a Leishmania SIR2 recombinant protein (LmSIR2) would affect T- and B-cell functions in a murine model. In vitro treatment of spleen cells from normal BALB/c mice with LmSIR2 showed increased expression of CD69 on B cells. This effect was not abolished by the addition of polymyxin B. Intravenous injection of LmSIR2 into BALB/c mice induced increased spleen B cell number by a factor of about approximately 1.6, whereas no modification occurred at the level of CD4(+) and CD8(+) cells. Furthermore, intraperitoneal injection of LmSIR2 alone without adjuvant into BALB/c mice or nude mice triggered the production of elevated levels of LmSIR2-specific antibodies. The analysis of specific isotype profiles showed a predominance of immunoglobulin G1 (IgG1) and IgG2a antibody responses in BALB/c mice, and IgM in nude mice. Moreover, the anti-LmSIR2 mouse antibodies in the presence of complement induced the in vitro lysis of L. infantum amastigotes. In the absence of complement, the antibodies induced significant inhibition of amastigotes developpement inside macrophages. Together, the current study provides the first evidence that a Leishmania protein belonging to the SIR2 family may play a role in the regulation of immune response through its capacity to trigger B-cell effector function.

Identification of Actinobacillus suis genes essential for the colonization of the upper respiratory tract of swine

Actinobacillus suis has emerged as an important opportunistic pathogen of high-health-status swine. A colonization challenge method was developed, and using PCR-based signature-tagged transposon mutagenesis, 13 genes belonging to 9 different functional classes were identified that were necessary for A. suis colonization of the upper respiratory tract of swine.

Characterization of the B-cell immune response elicited in BALB/c mice challenged with Neospora caninum tachyzoites

Activation of B cells occurring in hosts infected with protozoan parasites has been implicated either in protective or parasite-evasion immune-mediated mechanisms. Intraperitoneal inoculation of Neospora caninum tachyzoites into BALB/c mice induces an acute response characterized by a rapid increase in the numbers of CD69-expressing peritoneal and splenic B cells. This early B-cell stimulatory effect preceded an increase in the numbers of total and immunoglobulin-secreting splenic B cells and a rise in serum levels of N. caninum-specific immunoglobulins, predominantly of the immunoglobulin G2a (IgG2a) and IgM isotypes. Increased numbers of B cells expressing the costimulatory molecules CD80 and CD86 were also observed in the N. caninum-infected mice. The B-cell stimulatory effect observed in mice challenged with N. caninum tachyzoites was reduced in mice challenged with gamma-irradiated parasites. Contrasting with the peripheral B-cell expansion, a depletion of B-lineage cells was observed in the bone-marrow of the N. caninum-infected mice. Intradermal immunization of BALB/c mice with diverse N. caninum antigenic preparations although inducing the production of parasite-specific antibodies nevertheless impaired interferon-gamma (IFN-gamma) mRNA expression and caused lethal susceptibility to infection in mice inoculated with a non-lethal parasitic inoculum. This increased susceptibility to N. caninum was not observed in naïve mice passively transferred with anti-N. caninum antibodies. Taken together, these results show that N. caninum induces in BALB/c mice a parasite-specific, non-polyclonal, B-cell response, reinforce previous observations made by others showing that immunization with N. caninum whole structural antigens increases susceptibility to murine neosporosis and further stress the role of IFN-gamma in the host protective immune mechanisms against this parasite.

Antibodies against a Leishmania infantum peroxiredoxin as a possible marker for diagnosis of visceral leishmaniasis and for monitoring the efficacy of treatment

Diagnosis of leishmaniasis is frequently based on serological methods, such as direct agglutination, immunofluorescence tests and ELISA assays with Leishmania total extracts, as antigen, however due to highly inconclusive results, more reliable tests are needed. In the present study, the prevalence of antibodies to a number of recombinant proteins (LmSIR2, LmS3a, LimTXNPx, LicTXNPx and LiTXN1) highly conserved among Leishmania species, were evaluated by ELISA in Leishmania infantum infected children from an endemic area of Portugal. We found that sera from children patients had antibodies against the different recombinant proteins, LicTXNPx presented the highest immuno-reactivity compared to the other and the most often recognized in the case of acute visceral leishmaniasis (VL). Moreover, in children treated with meglumine antimoniate or amphotericin B, antibodies against some of the recombinant proteins declined, whereas conventional serology using crude extracts showed little or no difference between the pre- and post-treatment values. The highest reduction was observed in the case of antibodies against the LicTXNPx protein. These results suggest that the antibodies against LicTXNPx might be a useful constituent of a defined serological test for the diagnosis and the monitoring of the therapeutic response in VL. The monitoring and follow-up in a large-scale field trials of such marker in areas where leishmaniasis is endemic will lend support to this.

Comparison in gene expression of secretory human endometrium using laser microdissection

BACKGROUND

The endometrium prepares for implantation under the control of steroid hormones. It has been suggested that there are complicated interactions between the epithelium and stroma in the endometrium during menstrual cycle. In this study, we demonstrate a difference in gene expression between the epithelial and stromal areas of the secretory human endometrium using microdissection and macroarray technique.

METHODS

The epithelial and stromal areas were microdissected from the human endometrium during the secretory phase. RNA was extracted and amplified by PCR. Macroarray analysis of nearly 1000 human genes was carried out in this study. Some genes identified by macroarray analysis were verified using real-time PCR.

RESULTS

In this study, changes in expression <2.5-fold in three samples were excluded. A total of 28 genes displayed changes in expression from array data. Fifteen genes were strongly expressed in the epithelial areas, while 13 genes were strongly expressed in the stromal areas. The strongly expressed genes in the epithelial areas with a changes >5-fold were WAP four-disulfide core domain 2 (44.1 fold), matrix metalloproteinase 7 (40.1 fold), homeo box B5 (19.8 fold), msh homeo box homolog (18.8 fold), homeo box B7 (12.7 fold) and protein kinase C, theta (6.4 fold). On the other hand, decorin (55.6 fold), discoidin domain receptor member 2 (17.3 fold), tissue inhibitor of metalloproteinase 1 (9 fold), ribosomal protein S3A (6.3 fold), and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (5.2 fold) were strongly expressed in the stromal areas. WAP four-disulfide core domain 2 (19.4 fold), matrix metalloproteinase 7 (9.7-fold), decorin (16.3-fold) and tissue inhibitor of metalloproteinase 1 (7.2-fold) were verified by real-time PCR.

CONCLUSIONS

Some of the genes we identified with differential expression are related to the immune system. These results are telling us the new information for understanding the secretory human endometrium.

Host Cell Phenotypic Variability Induced by Trypanosomatid-Parasite-Released Immunomodulatory Factors: Physiopathological Implications

The parasitic protozoa Trypanosoma cruzi and Leishmania sp release a variety of molecules into their mammalian hosts (ESA: excretory-secretory products). The effects of these ESA on the host cell function may participate in the establishment of a successful infection, in which the parasite persists for a sufficient period of time to complete its life cycle. A number of regulatory components or processes originating from the parasite that control or regulate the metabolism and the growth of host cell have been identified. The purpose of the present review is to analyze some of the current data related to the parasite ESA that interfere with the host cell physiology. Special attention is given to members of conserved protein families demonstrating remarkable diversity and plasticity of function (ie, glutathione S-transferases and related molecules; members of the trans-sialidase and mucin family; and members of the ribosomal protein family). The identification of parasite target molecules and the elucidation of their mode of action toward the host cell represents a step forward in efforts aimed at an immunotherapeutic or pharmacological control of parasitic infection.

Inhibition of lymphocyte proliferation by prenylated flavones: artelastin as a potent inhibitor

Eight natural prenylated flavones, previously isolated from Artocarpus elasticus, were evaluated for their effect on the mitogenic response of human lymphocytes to PHA. They all exhibited a dose-dependent suppression effect. An interesting relationship was observed between their antiproliferative activity and their chemical structure. Indeed, the most potent flavones possessed a 3,3-dymethylallyl group (prenyl) at C-8, such as artelastin, which exhibited the highest antiproliferative activity. Studies of the mechanism underlying its effect revealed that artelastin had an irreversible inhibitory effect on the PHA-induced lymphocyte proliferation and could affect the course of the ongoing mitogenic response either at the initial induction phase or at the late phase of proliferation. This prenylated flavone was also shown to be a potent inhibitor of both T- and B-lymphocyte mitogen induced proliferation although B-mitogenic response was the more sensitive one. Artelastin did not affect either the basal levels of the early marker of activation CD69 on non-stimulated splenocytes or its expression on ConA- or LPS-stimulated splenocytes. However, it decreased the production of IFN-gamma, IL-2, IL-4 and IL-10 in ConA-stimulated splenocytes. Furthermore, artelastin had no effect on apoptosis of splenocytes.

Glutathione S-transferases and related proteins from pathogenic human parasites behave as immunomodulatory factors

There is a rapidly expanding interest into the glutathione S-transferases (GSTs) and the structurally related molecules. Many of the latter have been identified as members of conserved protein families sharing structural and some times functional properties being particularly involved in heat-shock response, drug resistance and carcinogenesis. Also, evidence is emerging that members of the GST super family from some pathogens could exert immunomodulatory functions toward the cell of the immune system, involving separate profiles of cytokine gene transcription and different patterns of cell growth, illustrating therefore the 'one gene-dual function' phenomenon. The implication of these biological properties for pathogenesis is discussed.