Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Requirement of microtubules for secretion of a micronemal protein CpTSP4 in the invasive stage of the apicomplexan Cryptosporidium parvum

The zoonotic Cryptosporidium parvum is a global contributor to infantile diarrheal diseases and opportunistic infections in immunocompromised or weakened individuals. Like other apicomplexans, it possesses several specialized secretory organelles, including micronemes, rhoptry, and dense granules. However, the understanding of cryptosporidial micronemal composition and secretory pathway remains limited. Here, we report a new micronemal protein in C. parvum, namely, thrombospondin (TSP)-repeat domain-containing protein-4 (CpTSP4), providing insights into these ambiguities. Immunostaining and enzyme-linked assays show that CpTSP4 is prestored in the micronemes of unexcysted sporozoites but secreted during sporozoite excystation, gliding, and invasion. In excysted sporozoites, CpTSP4 is also distributed on the two central microtubules unique to Cryptosporidium. The secretion and microtubular distribution could be completely blocked by the selective kinesin-5 inhibitors SB-743921 and SB-715992, resulting in the accumulation of CpTSP4 in micronemes. These support the kinesin-dependent microtubular trafficking of CpTSP4 for secretion. We also localize γ-tubulin, consistent with kinesin-dependent anterograde trafficking. Additionally, recombinant CpTSP4 displays nanomolar binding affinity to the host cell surface, for which heparin acts as one of the host ligands. A novel heparin-binding motif is identified and validated biochemically for its contribution to the adhesive property of CpTSP4 by peptide competition assays and site-directed mutagenesis. These findings shed light on the mechanisms of intracellular trafficking and secretion of a cryptosporidial micronemal protein and the interaction of a TSP-family protein with host cells.IMPORTANCECryptosporidium parvum is a globally distributed apicomplexan parasite infecting humans and/or animals. Like other apicomplexans, it possesses specialized secretory organelles in the zoites, in which micronemes discharge molecules to facilitate the movement and invasion of zoites. Although past and recent studies have identified several proteins in cryptosporidial micronemes, our understanding of the composition, secretory pathways, and domain-ligand interactions of micronemal proteins remains limited. This study identifies a new micronemal protein, namely, CpTSP4, that is discharged during excystation, gliding, and invasion of C. parvum sporozoites. The CpTSP4 secretion depends on the intracellular trafficking on the two Cryptosporidium-unique microtubes that could be blocked by kinesin-5/Eg5 inhibitors. Additionally, a novel heparin-binding motif is identified and biochemically validated, which contributes to the nanomolar binding affinity of CpTSP4 to host cells. These findings indicate that kinesin-dependent microtubular trafficking is critical to CpTSP4 secretion, and heparin/heparan sulfate is one of the ligands for this micronemal protein.

A heparin-binding protein of Plasmodium berghei is associated with merozoite invasion of erythrocytes

BACKGROUND

Malaria caused by Plasmodium species is a prominent public health concern worldwide, and the infection of a malarial parasite is transmitted to humans through the saliva of female Anopheles mosquitoes. Plasmodium invasion is a rapid and complex process. A critical step in the blood-stage infection of malarial parasites is the adhesion of merozoites to red blood cells (RBCs), which involves interactions between parasite ligands and receptors. The present study aimed to investigate a previously uncharacterized protein, PbMAP1 (encoded by PBANKA_1425900), which facilitates Plasmodium berghei ANKA (PbANKA) merozoite attachment and invasion via the heparan sulfate receptor.

METHODS

PbMAP1 protein expression was investigated at the asexual blood stage, and its specific binding activity to both heparan sulfate and RBCs was analyzed using western blotting, immunofluorescence, and flow cytometry. Furthermore, a PbMAP1-knockout parasitic strain was established using the double-crossover method to investigate its pathogenicity in mice.

RESULTS

The PbMAP1 protein, primarily localized to the P. berghei membrane at the merozoite stage, is involved in binding to heparan sulfate-like receptor on RBC surface of during merozoite invasion. Furthermore, mice immunized with the PbMAP1 protein or passively immunized with sera from PbMAP1-immunized mice exhibited increased immunity against lethal challenge. The PbMAP1-knockout parasite exhibited reduced pathogenicity.

CONCLUSIONS

PbMAP1 is involved in the binding of P. berghei to heparan sulfate-like receptors on RBC surface during merozoite invasion.

Unravelling Strain-Specific Modifications of Toxoplasma gondii tRNA and sncRNA Using LC-MS/MS

Many RNA modifications have been detected in rRNA, tRNA and small noncoding RNA (sncRNA) as well as in low-abundance RNA species such mRNA. Although RNA modifications play roles in many cellular and biological processes in various domains of life, knowledge about the diversity and role of RNA modifications in Toxoplasma gondii is limited. In this study, RNA modifications in three T. gondii strains (RH type I, PRU type II, and VEG type III) with distinct virulence abilities were determined by liquid chromatography-tandem mass spectrometry. We compared the levels of modifications of four nucleotides in tRNA and sncRNA, characterized RNA modification patterns of different T. gondii strains, and determined the diversity of RNA modifications. We detected and quantified 22 modified nucleosides in both tRNA and sncRNA. Significant differences in the diversity of the modified nucleosides were found between the three T. gondii strains. RNA modifications were correlated with the expression of many T. gondii virulence proteins. Some of the identified modifications (e.g., 2'-O-methylinosine, pseudouridine) play a role in mediating the host-parasite interaction. These results provide novel insight into the global modifications in tRNA and sncRNA, and the diversity of RNA modifications between T. gondii strains with different virulence backgrounds. IMPORTANCE Although RNA modifications play roles in many cellular and developmental processes in various domains of life, knowledge about the patterns and functions of RNA modifications in T. gondii is limited. Here, a quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach was used to study global RNA modifications in T. gondii strains of distinct virulence backgrounds. We quantified 22 modified nucleosides in both tRNA and sncRNA. Significant T. gondii strain-specific differences in RNA modifications were detected. More tRNA modifications correlated with T. gondii virulence proteins than sncRNA modifications. RNA modifications were significantly correlated with virulence proteins. Our data provide the first comprehensive profiling of the modifications tRNA and sncRNA in T. gondii, expanding the diversity of RNA modifications in this parasite and suggesting new regulators for modulating its virulence.

Harnessing Human Papillomavirus’ Natural Tropism to Target Tumors

Human papillomaviruses (HPV) are small non-enveloped DNA tumor viruses established as the primary etiological agent for the development of cervical cancer. Decades of research have elucidated HPV’s primary attachment factor to be heparan sulfate proteoglycans (HSPG). Importantly, wounding and exposure of the epithelial basement membrane was found to be pivotal for efficient attachment and infection of HPV in vivo. Sulfation patterns on HSPG’s become modified at the site of wounds as they serve an important role promoting tissue healing, cell proliferation and neovascularization and it is these modifications recognized by HPV. Analogous HSPG modification patterns can be found on tumor cells as they too require the aforementioned processes to grow and metastasize. Although targeting tumor associated HSPG is not a novel concept, the use of HPV to target and treat tumors has only been realized in recent years. The work herein describes how decades of basic HPV research has culminated in the rational design of an HPV-based virus-like infrared light activated dye conjugate for the treatment of choroidal melanoma.

Transcriptional signatures of clonally derived Toxoplasma tachyzoites reveal novel insights into the expression of a family of surface proteins

Toxoplasma gondii has numerous, large, paralogous gene families that are likely critical for supporting its unparalleled host range: nearly any nucleated cell in almost any warm-blooded animal. The SRS (SAG1-related sequence) gene family encodes over 100 proteins, the most abundant of which are thought to be involved in parasite attachment and, based on their stage-specific expression, evading the host immune response. For most SRS proteins, however, little is understood about their function and expression profile. Single-parasite RNA-sequencing previously demonstrated that across an entire population of lab-grown tachyzoites, transcripts for over 70 SRS genes were detected in at least one parasite. In any one parasite, however, transcripts for an average of only 7 SRS genes were detected, two of which, SAG1 and SAG2A, were extremely abundant and detected in virtually all. These data do not address whether this pattern of sporadic SRS gene expression is consistently inherited among the progeny of a given parasite or arises independently of lineage. We hypothesized that if SRS expression signatures are stably inherited by progeny, subclones isolated from a cloned parent would be more alike in their expression signatures than they are to the offspring of another clone. In this report, we compare transcriptomes of clonally derived parasites to determine the degree to which expression of the SRS family is stably inherited in individual parasites. Our data indicate that in RH tachyzoites, SRS genes are variably expressed even between parasite samples subcloned from the same parent within approximately 10 parasite divisions (72 hours). This suggests that the pattern of sporadically expressed SRS genes is highly variable and not driven by inheritance mechanisms, at least under our conditions.

Antiparasitic Effects of Sulfated Polysaccharides from Marine Hydrobionts

This review presents materials characterizing sulfated polysaccharides (SPS) of marine hydrobionts (algae and invertebrates) as potential means for the prevention and treatment of protozoa and helminthiasis. The authors have summarized the literature on the pathogenetic targets of protozoa on the host cells and on the antiparasitic potential of polysaccharides from red, brown and green algae as well as certain marine invertebrates. Information about the mechanisms of action of these unique compounds in diseases caused by protozoa has also been summarized. SPS is distinguished by high antiparasitic activity, good solubility and an almost complete absence of toxicity. In the long term, this allows for the consideration of these compounds as effective and attractive candidates on which to base drugs, biologically active food additives and functional food products with antiparasitic activity.

Congenital Transmission of Apicomplexan Parasites: A Review

Apicomplexans are a group of pathogenic protists that cause various diseases in humans and animals that cause economic losses worldwide. These unicellular eukaryotes are characterized by having a complex life cycle and the ability to evade the immune system of their host organism. Infections caused by some of these parasites affect millions of pregnant women worldwide, leading to various adverse maternal and fetal/placental effects. Unfortunately, the exact pathogenesis of congenital apicomplexan diseases is far from being understood, including the mechanisms of how they cross the placental barrier. In this review, we highlight important aspects of the diseases caused by species of Plasmodium, Babesia, Toxoplasma, and Neospora, their infection during pregnancy, emphasizing the possible role played by the placenta in the host-pathogen interaction.

Cell invasion by intracellular parasites - the many roads to infection

Intracellular parasites from the genera Toxoplasma, Plasmodium, Trypanosoma, Leishmania and from the phylum Microsporidia are, respectively, the causative agents of toxoplasmosis, malaria, Chagas disease, leishmaniasis and microsporidiosis, illnesses that kill millions of people around the globe. Crossing the host cell plasma membrane (PM) is an obstacle these parasites must overcome to establish themselves intracellularly and so cause diseases. The mechanisms of cell invasion are quite diverse and include (1) formation of moving junctions that drive parasites into host cells, as for the protozoans Toxoplasma gondii and Plasmodium spp., (2) subversion of endocytic pathways used by the host cell to repair PM, as for Trypanosoma cruzi and Leishmania, (3) induction of phagocytosis as for Leishmania or (4) endocytosis of parasites induced by specialized structures, such as the polar tubes present in microsporidian species. Understanding the early steps of cell entry is essential for the development of vaccines and drugs for the prevention or treatment of these diseases, and thus enormous research efforts have been made to unveil their underlying biological mechanisms. This Review will focus on these mechanisms and the factors involved, with an emphasis on the recent insights into the cell biology of invasion by these pathogens.

Identification of Host Proteins Interacting with Toxoplasma gondii SAG1 by Yeast Two-Hybrid Assay

Toxoplasma gondii is one of the most successful human pathogens. To eliminate the infection, identification of receptors or binding partners from humans is indeed urgent. T. gondii surface antigen is the ultimate component involved during the attachment of parasite into host cell. However, mechanism of invasion between SAG and host-cell membrane remains unclear. Yeast two-hybrid experiment was used to identify the binding partners from cDNA human library by using T. gondii SAG1 as bait. Mated yeast cells were plated on DDO/X plates to confirm only prey plasmid that expressing interacting protein was selected. We detected 39 clones interacted with SAG1 based on a series of the selection procedures. After colony PCR, only 29 clones were positive and subsequently sent for sequencing. The yeast plasmids for true positive clones were rescued by transformation into E. coli TOP 10F' cells. Twenty-two clones were further examined by small-scale Y2H experiment. The results indicated that a strong interaction existed between Homo sapiens lysine-rich coil-coiled and SAG1 protein, which could activate the expressions of the reporter genes in diploid yeast. Co-immunoprecipitation experiment result indicated the binding between this prey and SAG1 protein was significant (Mann-Whitney U test, Z = - 1.964, P = 0.05). H. sapiens lysine-rich coil-coiled protein was found to be interacted with SAG1. This prey protein may serve as the potential drug target in vaccination study.

Demystifying a hexuronic acid ligand that recognizes Toxoplasma gondii and blocks its invasion into host cells

Toxoplasma gondii is a ubiquitous eukaryotic pathogen responsible for toxoplasmosis in humans and animals. This parasite is an obligate intracellular pathogen and actively invades susceptible host cells, a process which is mediated by specific receptor-ligand interactions. Here, we have identified an unnatural 2,4-disulfated d-glucuronic acid (Di-S-GlcA), a hexuronic acid composed of heparin/heparan sulfate, as a potential carbohydrate ligand that can selectively bind to T. gondii parasites. More importantly, the gelatin conjugated Di-S-GlcA multivalent probe displayed strong inhibition of parasite entry into host cells. These results open perspective for the future use of Di-S-GlcA epitopes in biomedical applications against toxoplasmosis.

FUT3 and FUT2 genotyping and glycoconjugate profile Lewisb as a protective factor to Toxoplasma gondii infection

The interaction between the ABO, FUT2 and FUT3 genes results in the synthesis of different glycoconjugates profiles expressed in gastrointestinal tract. Moreover, the protozoan Toxoplasma gondii, which causes toxoplasmosis, utilizes this organ as an infection route. We analyzed the frequencies of the different glycoconjugate profiles which were determined by phenotyping ABO and genotyping the status secretor (FUT2; substitution G428A) and Lewis (FUT3; substitution T202C and C314T) histo-blood systems, assessed by PCR-RFLP and PCR-SSP, respectively. A total of 244 pregnant women (G1: Seropositive; G2: Seronegative) for IgG T. gondii antibodies were enrolled. IgG anti-T. gondii antibodies were determined by ELISA. G1 was composed of 158 (64.8%) sample and G2 by 86 (36.2%). The glycoconjugate profile was accessed in 151 seropositive and 85 seronegative samples by the combination of ABO and Lewis phenotyping as well as FUT2 and FUT3 genotyping. In G1, 36 (22.8%) presented the glycoconjugate profile ALeb, 5 (3.3%) A, 13 (8.6) BLeb, 1 (0.6%) B, 41 (27.1%) Leb, 13(8.6%) H, 38(25.2%) Lea and 4 (2.6%) Lec. G2 was composed of 13 (15.3%) of ALeb, 15 (17.6%) BLeb, 1 (1.2%) B, 42 (49,4%) Leb and 14 (16.5) Lea. H and Lec glycoconjugate profiles were not found in G2. The frequencies of the glycoconjugates profiles Leb (p = 0.001) and H (p = 0.005) were significantly different compared between G1 and G2. The glycoconjugate profile H inferred from the ABO phenotyping and FUT3 and FUT2 genotyping is associated with infection by T. gondii in pregnant women and the Leb profile appears to protect the infection by this parasite.

ROP9, MIC3, and SAG2 are heparin-binding proteins in Toxoplasma gondii and involved in host cell attachment and invasion

Toxoplasma gondii (T. gondii) is an obligatory intracellular parasite that can infect varieties of warm-blooded animals, including humans and birds. Heparan sulfate (HS) is widely distributed on the eukaryotic cell surface of vertebrates and can inhibit T. gondii invasion. In this study, we investigated the transcription and expression of the level of TgROP9, TgMIC3, and TgSAG2 in T. gondii RH strain, and found that the expression levels of these three proteins in invading parasites were higher compared to those free ranging parasites. The recombinant proteins showed specific binding activity to both heparin and host cell surface. Incubation of these proteins with the host cells could block T. gondiiinvasion. Furthermore, protein-specific antibodies also blocked parasite invasion. Antibodies in the sera of T. gondii infected individuals recognized the recombinant TgROP9, TgMIC3, and TgSAG2, which suggested the exposure of these proteins to human immune system. Mice immunized with the three proteins exhibited protective immunity against lethal challenge. The data collectively suggested that these parasitic proteins may be used as candidate antigens for development of anti-toxoplasmosis vaccine.

Therapeutic strategies to target microbial protein-glycosaminoglycan interactions

Glycans are involved in a plethora of human pathologies including infectious diseases. Especially, glycosaminoglycans (GAGs), like heparan sulfate and chondroitin sulfate, have been found to be involved in different crucial stages of microbial invasion. Here, we review various therapeutic approaches, which target the interface of host GAGs and microbial proteins and discuss their limitations and challenges for drug development.

Toxoplasma gondii RON4 binds to heparan sulfate on the host cell surface

Toxoplasma gondii rhoptry neck protein 4 (TgRON4) is a component of the moving junction, a key structure for host cell invasion. We previously showed that host cellular β-tubulin is a binding partner of TgRON4 in the invasion process. Here, to identify other binding partners of TgRON4 in the host cell, we examined the binding of TgRON4 to components of the host cell surface. TgRON4 binds to various mammalian cells, but this binding disappeared in glycosaminoglycan- and heparan sulfate-deficient CHO cells and after heparitinase treatment of mammalian cells. The C-terminal half of TgRON4 showed relatively strong binding to cells and heparin agarose. A glycoarray assay indicated that TgRON4 binds to heparin and modified heparin derivatives. Immunoprecipitation of T. gondii-infected CHO cell lysates showed that TgRON4 interacts with glypican 1 during Toxoplasma invasion. This interaction suggests a role for heparan sulfate in parasite invasion.

The Cryptosporidium parvum C-Type Lectin CpClec Mediates Infection of Intestinal Epithelial Cells via Interactions with Sulfated Proteoglycans

The apicomplexan parasite Cryptosporidium causes significant diarrheal disease worldwide. Effective anticryptosporidial agents are lacking, in part because the molecular mechanisms underlying Cryptosporidium-host cell interactions are poorly understood. Previously, we identified and characterized a novel Cryptosporidium parvum C-type lectin domain-containing mucin-like glycoprotein, CpClec. In this study, we evaluated the mechanisms underlying interactions of CpClec with intestinal epithelial cells by using an Fc-tagged recombinant protein. CpClec-Fc displayed Ca(2+)-dependent, saturable binding to HCT-8 and Caco-2 cells and competitively inhibited C. parvum attachment to and infection of HCT-8 cells. Binding of CpClec-Fc was specifically inhibited by sulfated glycosaminoglycans, particularly heparin and heparan sulfate. Binding was reduced after the removal of heparan sulfate and following the inhibition of glycosaminoglycan synthesis or sulfation in HCT-8 cells. Like CpClec-Fc binding, C. parvum attachment to and infection of HCT-8 cells were inhibited by glycosaminoglycans and were reduced after heparan sulfate removal or inhibition of glycosaminoglycan synthesis or sulfation. Lastly, CpClec-Fc binding and C. parvum sporozoite attachment were significantly decreased in CHO cell mutants defective in glycosaminoglycan synthesis. Together, these results indicate that CpClec is a novel C-type lectin that mediates C. parvum attachment and infection via Ca(2+)-dependent binding to sulfated proteoglycans on intestinal epithelial cells.

Proteomic analysis of Eimeria acervulina sporozoite proteins interaction with duodenal epithelial cells by shotgun LC-MS/MS

Although it has been known for many years that Eimeria acervulina (E. acervulina) initiates infection by invading the duodenal epithelial cells of chicken, the key protein molecules and the mechanisms of the parasite in invading are unknow. In this study, we found that 85 proteins of E. acervulina could bind with the chicken duodenal epithelial cells from Eimeria protein database. Among them, sixteen were identified only in Eimeria spp. correlation with invasion and evasion and 69 proteins were found in Eimeria spp. with more than 2 unique pep count. Nine out of the 16 proteins and 41 out of the 69 proteins were annotated according to Gene Ontology Annotation in terms of molecular function, biological process, and cellular localization. Most of the 9 annotated proteins occurred in binding, catalytic activity and cellular process whereas, 29 (70.73%) out of the 41 proteins had binding activity and 20 proteins (48.78%) had catalytic activity. The findings provided an insight into the interactive relationship between E. acervulina and host cells and will shed new lights on the understanding of molecular mechanisms of E. acervulina invasion and pathogenesis.

Heparin interacts with elongation factor 1α of Cryptosporidium parvum and inhibits invasion

Cryptosporidium parvum is an apicomplexan parasite that can cause serious watery diarrhea, cryptosporidiosis, in human and other mammals. C. parvum invades gastrointestinal epithelial cells, which have abundant glycosaminoglycans on their cell surface. However, little is known about the interaction between C. parvum and glycosaminoglycans. In this study, we assessed the inhibitory effect of sulfated polysaccharides on C. parvum invasion of host cells and identified the parasite ligands that interact with sulfated polysaccharides. Among five sulfated polysaccharides tested, heparin had the highest, dose-dependent inhibitory effect on parasite invasion. Heparan sulfate-deficient cells were less susceptible to C. parvum infection. We further identified 31 parasite proteins that potentially interact with heparin. Of these, we confirmed that C. parvum elongation factor 1α (CpEF1α), which plays a role in C. parvum invasion, binds to heparin and to the surface of HCT-8 cells. Our results further our understanding of the molecular basis of C. parvum infection and will facilitate the development of anti-cryptosporidial agents.

Secreted Toxoplasma gondii molecules interfere with expression of MHC-II in interferon gamma-activated macrophages

The obligate intracellular protozoan parasite Toxoplasma gondii interferes with major histocompatibility complex class II antigen presentation to dampen host CD4(+) T cell responses. While it is known that T. gondii inhibits major histocompatibility complex class II gene transcription and expression in infected host cells, the mechanism of this host manipulation is unknown. Here, we show that soluble parasite proteins inhibit IFNγ-induced expression of major histocompatibility complex class II on the surface of the infected cell in a dose-dependent response that was abolished by protease treatment. Subcellular fractionation of T. gondii tachyzoites revealed that the major histocompatibility complex class II inhibitory activity co-partitioned with rhoptries and/or dense granules. However, parasite mutants deleted for single rhoptries or dense granules genes (ROP1, 4/7, 14, 16 and 18 or GRA 2-9 and 12 knock-out strains) retained the ability to inhibit expression of major histocompatibility complex class II. In addition, excreted/secreted antigens released by extracellular tachyzoites displayed immunomodulatory activity characterized by an inhibition of major histocompatibility complex class II expression, and reduced expression and release of TNFα by macrophages. Tandem MS analysis of parasite excreted/secreted antigens generated a list of T. gondii secreted proteins that may participate in major histocompatibility complex class II inhibition and the modulation of host immune functions.

A comparative study on the heparin-binding proteomes of Toxoplasma gondii and Plasmodium falciparum

Toxoplasma gondii is an obligatory intracellular apicomplexan parasite which exploits host cell surface components in cell invasion and intracellular parasitization. Sulfated glycans such as heparin and heparan sulfate have been reported to inhibit cell invasion by T. gondii and other apicomplexan parasites such as Plasmodium falciparum. The aim of this study was to investigate the heparin-binding proteome of T. gondii. The parasite-derived components were affinity-purified on the heparin moiety followed by MS fingerprinting of the proteins. The heparin-binding proteins of T. gondii and P. falciparum were compared based on functionality and affinity to heparin. Among the proteins identified, the invasion-related parasite ligands derived from tachyzoite/merozoite surface and the secretory organelles were prominent. However, the profiles of the proteins were different in terms of affinity to heparin. In T. gondii, the proteins with highest affinity to heparin were the intracellular components with functions of parasite development contrasted to that of P. falciparum, of which the rhoptry-derived proteins were prominently identified. The profiling of the heparin-binding proteins of the two apicomplexan parasites not only explained the mechanism of heparin-mediated host cell invasion inhibition, but also, to a certain extent, revealed that the action of heparin on the parasite extended after endocytosis.

The involvement of heparin in retinal infection by Toxoplasma gondii in a chick model revealed an ontogenetic-dependent pattern

This work aimed to test the influence of heparin on the susceptibility of retinal cells to Toxoplasma gondii infection. Primary cultures of retinas from chick embryos of 8 (E8) or 11 (E11) days and fibroblasts (control) were used. To determine the influence of heparin in T. gondii infection, tachyzoites of the RH strain were treated with heparin before addition in the culture. A monoclonal anti-heparin antibody was used to analyze the heparin distribution on fibroblast and retinal cell surfaces. Our results showed that retinal cells (E8 and E11) had a higher infection rate than fibroblasts (91% and 24% versus 13%, respectively). Pre-treatment of T. gondii with heparin decreased infection of E8 retinal cells when compared with non-treated parasites (45% versus 91%, respectively), but not of E11 cells (35% versus 48%). In accordance, retinal cells presented an intense heparin staining by immunofluorescence assay. In conclusion, retinal cells from chick embryos were more susceptible to infection by T. gondii compared to fibroblasts and, pre-treatment of tachyzoites with heparin decreased the number of infected cells and parasite burden particularly for E8 retinal cells.