Expanding the Known Repertoire of C-Type Lectin Receptors Binding to Toxoplasma gondii Oocysts Using a Modified High-Resolution Immunofluorescence Assay

Proteomic identification of a Toxoplasma gondii sporozoite-specific antigen using HDAC3 inhibitor-treated tachyzoites as surrogate

The apicomplexan parasite Toxoplasma gondii has a complex life cycle. Access to sexual stages and sporozoite-containing oocysts, essential for studying the parasite's environmental transmission, is limited and requires animal experiments with cats. Thus, alternatives and resource-efficient methods are needed. Several molecular factors and transcriptional switches responsible for differentiation have been identified in recent years. In tachyzoites, drug-induced inhibition of the histone deacetylase HDAC3, or genetic depletion of transcription factors regulating HDAC3, leads to the expression of genes that are specific to sexual stages and oocysts. Here, we applied this concept and showed that the commercially available HDAC3 inhibitor apicidin could be used to identify the hitherto unknown antigen of the sporozoite-specific monoclonal antibody G1/19 in tachyzoites. Using mass spectrometry of immunoprecipitated G1/19 target protein from apicidin-treated cultures, we identified it as SporoSAG. In addition, for the much less abundant sporozoite-specific protein LEA860, apicidin treatment was still sufficient to induce a detectable protein level in immunofluorescence microscopy. We also discuss further applications and the limitations of this approach. This allows to overcome issues with the paucity of material of sexual stages and oocysts from T. gondii to some extent without the need for cat-derived material.

Trend in serological and molecular diagnostic methods for Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii, an intracellular parasite, is a significant cause of zoonotic disease, with an estimated one-third of the world's human population believed to be infected. T. gondii is transmitted to humans through the consumption of contaminated water, soil, vegetables, fruits, shellfish or undercooked meat, and can also be passed from human to human through vertical transmission, transplants and blood transfusion. While T. gondii infection typically manifests mild symptoms such as colds among immunocompetent individuals, it can prove lethal for those with weakened immune systems.

METHODS

To summarize the diagnostic methods for Toxoplasma gondii infection, we performed a literature search on PubMed from 1948 to 2023 using the keywords "T. gondii serological diagnosis" or "T. gondii molecular diagnosis".

RESULTS

Rapid and accurate diagnosis of T. gondii infection is imperative. Although a diagnostic kit is currently commercially available, there are a number of disadvantages to the validation principles applied to each diagnostic kit. Consequently, multiple diagnostic methods are concurrently employed to offset these limitations. Serological methods for diagnosing T. gondii infection include the Dye Test (DT), Agglutination Test (AT), Modified Agglutination Test (MAT), Latex Agglutination Test (LAT), Enzyme-Linked Immunosorbent Assay (ELISA), and Western Blot. Meanwhile, molecular methods such as polymerase chain reaction (PCR), nested PCR, real-time PCR, loop-mediated isothermal amplification (LAMP), multiplex PCR, and PCR-restriction fragment length polymorphism (PCR-RFLP) are also utilized. Each of these methods possess its own set of advantages and disadvantages.

CONCLUSIONS

By summarizing the advantages and disadvantages of different diagnostic techniques, it is hoped that the epidemiology, prevention, and control of toxoplasmosis will be improved in the future through the use of appropriate technologies.

Pharmacological properties of extracts and prenylated isoflavonoids from the fruits of Osage orange (Maclura pomifera (Raf.) C.K.Schneid.)

Osage orange trees (Maclura pomifera (Raf.) C.K.Schneid.) are distributed worldwide, particularly in south-east states of the USA. They produce large quantities of strong yellow fruits, bigger than oranges, but these fruits are inedible, with an acid milky juice which is little consumed by birds and insects. Extracts prepared from Osage orange fruits (hedge apple) have revealed a range of pharmacological properties of interest in human and veterinary medicine. In addition, Osage orange extracts can be used in agriculture and aquaculture, and as dyeing agent for the textile industry. Extracts contain potent antioxidant compounds, notably the isoflavonoids pomiferin and auriculasin, together with other terpenoids and flavonoids. The structural characteristics and pharmacological properties of the major prenylated isoflavones isolated from M. pomifera are discussed here, with a focus on the two phenolic compounds osajin and warangalone, and the two catechol analogues pomiferin and auriculasin. The mechanisms at the origin of their potent antioxidant and anti-inflammatory effects are presented, notably inhibition of xanthine oxidase, phosphodiesterase 5A and kinases such as RKS2 and kRAS. Osajin and auriculasin display marked anticancer properties, owing to their ability to inhibit tumor cell proliferation, migration and tumor angiogenesis. Different molecular mechanisms are discussed, including osajin‑copper complexation and binding to quadruplex DNA. An overview of the mechanism of action of the prenylated isoflavones from Osage orange is presented, with the objective to promote their knowledge and to raise opportunities to better exploit the fruits of Osage orange, abundant but largely neglected at present.

Limited value of current and new in silico predicted oocyst-specific proteins of Toxoplasma gondii for source-attributing serology

Toxoplasma gondii is a zoonotic parasite infecting all warm-blooded animals, including humans. The contribution of environmental contamination by T. gondii oocysts to infections is understudied. The aim of the current work was to explore T. gondii serology as a means of attributing the source of infection using a robust stepwise approach. We identified in silico thirty-two promising oocyst-specific antigens from T. gondii ´omics data, recombinantly expressed and purified them and validated whether serology based on these proteins could discriminate oocyst- from tissue cyst-driven experimental infections. For this, three well-characterized serum panels, sampled from 0 to 6 weeks post-infection, from pigs and sheep experimentally infected with T. gondii oocysts or tissue cysts, were used. Candidate proteins were initially screened by Western blot with sera from pigs or sheep, infected for different times, either with oocysts or tissue cysts, as well as non-infected animals. Only the recombinant proteins TgCCp5A and TgSR1 provoked seroconversion upon infection and appeared to discriminate between oocyst- and tissue cyst-driven infections with pig sera. They were subsequently used to develop an enzyme-linked immunosorbent assay test for pigs. Based on this assay and Western blot analyses, a lack of stage specificity and low antigenicity was observed with all pig sera. The same was true for proteins TgERP, TgSporoSAG, TgOWP1 and TgOWP8, previously described as source-attributing antigens, when analyzed using the whole panels of sera. We conclude that there is currently no antigen that allows the discrimination of T. gondii infections acquired from either oocysts or tissue cysts by serological tests. This work provides robust new knowledge that can inform further research and development toward source-attributing T. gondii serology.

CLEC4A and CLEC12B C-type lectin receptors mediate interactions with Pneumocystis cell wall components

Introduction. C-type lectin receptors (CLRs) are prominently expressed on myeloid cells where they perform multiple functions including serving as pattern recognition receptors (PRRs) to drive innate as well as adaptive immunity to pathogens. Depending on the presence of a tyrosine-based signalling motif, CLR-microbial pathogen engagement may result in either anti- or pro-inflammatory signalling.Impact statement. In this manuscript, we report our laboratory study of two novel CLRs that recognize Pneumocystis murina cell wall homogenates (CWH) and a purified Pneumocystis carinii cell wall fraction (CWF).Aim. To study the potential of newly generated hFc-CLR fusions on binding to Pneumocystis murina CWHs and P. carinii CWFs and subsequent downstream inflammatory signalling analysis.Methods. Newly generated hFc-CLR fusion CLEC4A and CLEC12B were screened against P. murina CWHs and P. carinii CWFs preparations via modified ELISA. Immunofluorescence assay (IFA) was utilized to visualize hFc-CLR fusion binding against intact fixed fungal life forms to verify results. Quantitative PCR (q-PCR) analysis of lung mRNA from the mouse immunosuppressed Pneumocystis pneumonia (PCP) model versus uninfected mice was employed to detect possible changes in the respective Clec4a and Clec12b transcripts. Lastly, siRNA technology of both CLRs was conducted to determine effects on downstream inflammatory events in mouse macrophages stimulated in the presence of P. carinii CWFs.Results. We determined that both CLEC4A and CLEC12B hFc-CLRs displayed significant binding with P. murina CWHs and P. carinii CWFs. Binding events showed significant binding to both curdlan and laminarin, both polysaccharides containing β-(1,3) glucans as well as N-acetylglucosamine (GlcNAc) residues and modest yet non-significant binding to the negative control carbohydrate dextran. IFA with both CLR hFc-fusions against whole P. murina life forms corroborated these findings. Lastly, we surveyed the mRNA expression profiles of both CLRs tested above in the mouse immunosuppressed Pneumocystis pneumonia (PCP) model and determined that both CLRs were significantly up regulated during infection. Lastly, siRNA of both CLRs in the mouse RAW macrophage cell line was conducted and results demonstrated that silencing of Clec4a resulted in no significant changes in TNF-alpha generation in P. carinii CWF stimulated macrophages. On the contrary, silencing of Clec12b CLR resulted in significant decreases in TNF-alpha in RAW cells stimulated with the same CWF.Conclusion. The data presented here provide new members of the CLRs family recognizing Pneumocystis. Future studies using CLEC4A and/or CLEC12B deficient mice in the PCP mouse model should provide further insights into the host immunological response to Pneumocystis.

Understanding inhibitory receptor function in neutrophils through the lens of CLEC12A

Neutrophils are the first leukocytes recruited from the circulation in response to invading pathogens or injured cells. To eradicate pathogens and contribute to tissue repair, recruited neutrophils generate and release a host of toxic chemicals that can also damage normal cells. To avoid collateral damage leading to tissue injury and organ dysfunction, molecular mechanisms evolved that tightly control neutrophil response threshold to activating signals, the strength and location of the response, and the timing of response termination. One mechanism of response control is interruption of activating intracellular signaling pathways by the 20 inhibitory receptors expressed by neutrophils. The two inhibitory C-type lectin receptors expressed by neutrophils, CLEC12A and DCIR, exhibit both common and distinct molecular and functional mechanisms, and they are associated with different diseases. In this review, we use studies on CLEC12A as a model of inhibitory receptor regulation of neutrophil function and participation in disease. Understanding the molecular mechanisms leading to inhibitory receptor specificity offers the possibility of using physiologic control of neutrophil functions as a pharmacologic tool to control inflammatory diseases.

Dual RNA Sequencing Reveals Key Events When Different Giardia Life Cycle Stages Interact With Human Intestinal Epithelial Cells In Vitro

Giardia intestinalis is a protozoan parasite causing diarrheal disease, giardiasis, after extracellular infection of humans and other mammals’ intestinal epithelial cells (IECs) of the upper small intestine. The parasite has two main life cycle stages: replicative trophozoites and transmissive cysts. Differentiating parasites (encysting cells) and trophozoites have recently been shown to be present in the same regions of the upper small intestine, whereas most mature cysts are found further down in the intestinal system. To learn more about host-parasite interactions during Giardia infections, we used an in vitro model of the parasite’s interaction with host IECs (differentiated Caco-2 cells) and Giardia WB trophozoites, early encysting cells (7 h), and cysts. Dual RNA sequencing (Dual RNAseq) was used to identify differentially expressed genes (DEGs) in both Giardia and the IECs, which might relate to establishing infection and disease induction. In the human cells, the largest gene expression changes were found in immune and MAPK signaling, transcriptional regulation, apoptosis, cholesterol metabolism and oxidative stress. The different life cycle stages of Giardia induced a core of similar DEGs but at different levels and there are many life cycle stage-specific DEGs. The metabolic protein PCK1, the transcription factors HES7, HEY1 and JUN, the peptide hormone CCK and the mucins MUC2 and MUC5A are up-regulated in the IECs by trophozoites but not cysts. Cysts specifically induce the chemokines CCL4L2, CCL5 and CXCL5, the signaling protein TRKA and the anti-bacterial protein WFDC12. The parasite, in turn, up-regulated a large number of hypothetical genes, high cysteine membrane proteins (HCMPs) and oxidative stress response genes. Early encysting cells have unique DEGs compared to trophozoites (e.g. several uniquely up-regulated HCMPs) and interaction of these cells with IECs affected the encystation process. Our data show that different life cycle stages of Giardia induce different gene expression responses in the host cells and that the IECs in turn differentially affect the gene expression in trophozoites and early encysting cells. This life cycle stage-specific host-parasite cross-talk is an important aspect to consider during further studies of Giardia’s molecular pathogenesis.

Identification of Oocyst-Driven Toxoplasma gondii Infections in Humans and Animals through Stage-Specific Serology-Current Status and Future Perspectives

The apicomplexan zoonotic parasite Toxoplasma gondii has three infective stages: sporozoites in sporulated oocysts, which are shed in unsporulated form into the environment by infected felids; tissue cysts containing bradyzoites, and fast replicating tachyzoites that are responsible for acute toxoplasmosis. The contribution of oocysts to infections in both humans and animals is understudied despite being highly relevant. Only a few diagnostic antigens have been described to be capable of discriminating which parasite stage has caused an infection. Here we provide an extensive overview of the antigens and serological assays used to detect oocyst-driven infections in humans and animals according to the literature. In addition, we critically discuss the possibility to exploit the increasing knowledge of the T. gondii genome and the various 'omics datasets available, by applying predictive algorithms, for the identification of new oocyst-specific proteins for diagnostic purposes. Finally, we propose a workflow for how such antigens and assays based on them should be evaluated to ensure reproducible and robust results.

Fc-conjugated C-type lectin receptors: Tools for understanding host-pathogen interactions

The use of soluble fusion proteins of pattern recognition receptors (PRRs) used in the detection of exogenous and endogenous ligands has helped resolve the roles of PRRs in the innate immune response to pathogens, how they shape the adaptive immune response, and function in maintaining homeostasis. Using the immunoglobulin (Ig) crystallizable fragment (Fc) domain as a fusion partner, the PRR fusion proteins are soluble, stable, easily purified, have increased affinity due to the Fc homodimerization properties, and consequently have been used in a wide range of applications such as flow cytometry, screening of protein and glycan arrays, and immunofluorescent microscopy. This review will predominantly focus on the recognition of pathogens by the cell membrane-expressed glycan-binding proteins of the C-type lectin receptor (CLR) subgroup of PRRs. PRRs bind to conserved pathogen-associated molecular patterns (PAMPs), such as glycans, usually located within or on the outer surface of the pathogen. Significantly, many glycans structures are identical on both host and pathogen (e.g. the Lewis (Le) X glycan), allowing the use of Fc CLR fusion proteins with known endogenous and/or exogenous ligands as tools to identify pathogen structures that are able to interact with the immune system. Screens of highly purified pathogen-derived cell wall components have enabled identification of many unique PAMP structures recognized by CLRs. This review highlights studies using Fc CLR fusion proteins, with emphasis on the PAMPs found in fungi, bacteria, viruses, and parasites. The structure and unique features of the different CLR families is presented using examples from a broad range of microbes whenever possible.

Effect of household bleach on the structure of the sporocyst wall of Toxoplasma gondii

Toxoplasma gondii oocysts are responsible for food- and water-borne infections in humans worldwide. They are resistant to common chemical disinfectants, including chlorinated products, presumably due to the structure and molecular nature of the oocyst wall but also the sporocyst wall. In this study, we used fluorescence microscopy and transmission electron microscopy to characterise the structure of both the oocyst and sporocyst walls, exposed to household bleach. Bleach removed the outer layer of the oocyst wall and the outer layer of the wall of sporocysts exposed due to rupture of the oocyst wall. The loss of the outer sporocyst wall layer was associated with a decrease in its autofluorescence, which can be linked to the degradation of dityrosine cross-link proteins, and loss of Maclura pomifera lectin-reactive glycoproteins. This study suggests that the inner layers of the oocyst and sporocyst walls are the main structures responsible for the resistance of the parasite to household bleach.