Review: Theileria schizonts induce fundamental alterations in their host cells

Malignant human thyroid neoplasms associated with blood parasitic (haemosporidian) infection

Investigation of archival cytological material obtained by cytologists during fine-needle aspiration biopsy in follicular, papillary, and medullary human thyroid cancers revealed haemosporidian (blood parasitic) infection. Haemosporidian infection was detected as exo- and intraerythrocytic stages of development in thyrocytes schizogony. The exoerythrocytic stage of development is represented as microschizonts in a thyroid needle biopsy specimen. Probably, blood parasitic infection is the common etiology for these pathologies. All biopsy material in medical laboratories was stained with RomanowskyGiemsa stain. To clarify the localization of nuclei (DNA) of thyrocytes and nuclei (DNA) of haemosporidian infection in cytological material following investigation of the entire set of smears, a selective series of original archival smears was stained (restained) with a Feulgen/Schiff reagent. Staining of smears with RomanowskyGiemsa stain is an adsorption method that enables re-use of the same smears for staining with a Feulgen/Schiff reagent where the fuchsin dye, after DNA hydrolysis by hydrochloric acid, is incorporated into DNA and stains it in redviolet (crimsonlilac) color. An intentionally unstained protoplasm of blood parasitic infection was present as a light band around erythrocyte nuclei. In follicular thyroid cancer, Feulgen staining of thyrocytes revealed nuclear DNA and parasitic DNA (haemosporidium nuclei) as point inclusions and rings and diffusely distributed in the thyrocyte cytoplasm. The thyrocyte cytoplasm and nuclei were vacuolated, with thyrocyte nuclei being deformed, flattened, and displaced to the cell periphery. The erythrocytes, which were initially stained with eosin (orange color), contained haemosporidian nuclei (DNA). In some cases, endoglobular inclusions in thyrocytes and erythrocytes were of the same size. In papillary thyroid cancer, we were able to localize the nuclear DNA of thyrocytes and the parasitic DNA as point inclusions and diffusely distributed in the thyrocyte cytoplasm. Two or more polymorphic nuclei may eccentrically occur in the hyperplastic cytoplasm. Haemosporidian microschizonts occurred circumnuclearly in thyrocytes and as an exoerythrocytic stage in the blood. The erythrocyte cytoplasm contained redviolet polymorphic haemosporidian nuclei (DNA). In medullary thyroid cancer, the hyperplastic cytoplasm of thyrocytes contained eccentrically located nuclei (DNA) of thyrocytes and small haemosporidian nuclei (DNA), which may occupy the whole thyrocyte. There were thyrocytes with vacuolated cytoplasm and pronounced nuclear polymorphism. The size of hyperplastic nuclei was several times larger than that of normal thyrocyte nuclei. The color of stained cytoplasmic and nuclear vacuoles of thyrocytes was less redviolet compared with that of surrounding tissues, which probably indicates the presence of parasitic DNA in them. The haemosporidian nuclear material in erythrocytes is represented by polymorphic nuclei, which may indicate the simultaneous presence of different pathogen species and/or generations in the blood. Intracellular parasitism of haemosporidian infection in thyrocytes (schizogony) associated with three thyroid cancers leads to pronounced cytoplasmic hyperplasia, cytoplasmic vacuolization, and nuclear vacuolization of the thyrocyte, followed by impaired secretory function. Multinucleated thyrocytes with incomplete cytokinesis appear. The absence of lytic death of the affected thyrocytes indicates that the contagium is able to control apoptosis and influence physiological functions of the cell. There is deformation of the nuclei, which leads to a decrease in their size, their flattening and displacement to the cell periphery, with high risk of DNA mutations and deletions in affected cells, reaching a neoplastic level.

Clinical and hematologic features of experimental theileriosis in roan calves (Hippotragus equinus)

Theileria sp. (sable) infection commonly causes significant calf mortality in endangered roan antelopes (Hippotragus equinus). Schizont-induced leukocyte transformation and systemic immune dysregulation with associated cytopenias characterizes theileriosis in livestock. Data on related hematologic alterations are scarce in roan antelopes. The objective of this study was to investigate temporal changes in selected clinical parameters and hematologic measurands in experimentally infected (EI) roan calves. Six of eight calves developed theileriosis after inoculation with a Theileria sp. (sable)-infected tick stabilate. Consecutive measures of rectal temperature, lymph node size, white blood cell count (WBC), packed cell volume (PCV), hemoglobin concentration, differential leukocyte counts, leukocyte and erythrocyte morphology and percentage parasitemia were recorded. Data were compared with 15 age-matched PCR-negative control calves and nine older immune animals that had recovered from natural infection. Two non-pyrexic EI calves recovered uneventfully. Six pyrexic calves were treated, four of which died. Time to pyrexia and/or observation of schizonts and piroplasms was approximately two weeks. Total WBCs were unchanged post-infection (PI); neutrophils and typical monocytes decreased whereas typical lymphocytes (Ls) and atypical mononuclear leukocytes (AMLs), which were grouped together, increased. Parasitized and non-parasitized lymphocyte and AML (L/AML) size increased significantly PI. Piroplasms occurred intermittently at low frequencies («1 % of erythrocytes) after infection. Fatally infected calves were dehydrated, anemic, and icteric with hemorrhages and multi-organ infiltration by AMLs. The PCV and hemoglobin concentration increased PI, and platelet clumps were consistently observed. Experimental acute theileriosis in roan antelopes follows a similar pattern of disease progression to that in domestic livestock. Parasitized and non-parasitized AMLs are pivotal to the pathogenesis and require phenotypic characterization if we are to further our understanding of disease progression and severity in roan antelopes.

Theileria annulata surface protein (TaSP) is a target of cyclin-dependent kinase 1 phosphorylation in Theileria annulata-infected cells

Leucoproliferative Theileria parasites possess the unique capability to transform their bovine host cell, resulting in tumour-like characteristics like uncontrolled proliferation. The molecular mechanisms underlying this parasite-dependent process are only poorly understood. In the current study, bioinformatic analysis of the Theileria annulata surface protein (TaSP) from different T. annulata isolates identified a conserved CDK1 phosphorylation motif T₁₃₁ PTK within the extracellular, polymorphic domain of TaSP. Phosphorylation assays with radioactively labelled ATP as well as ELISA-based experiments using a phospho-threonine-proline (pThr-Pro) antibody revealed, that CDK1-cyclin B specifically phosphorylates T₁₃₁ , identifying TaSP as a substrate in vitro. Confocal microscopy and proximity ligation assays suggest an interaction between CDK1 and TaSP in T. annulata-infected cells. Further studies demonstrated a nearly complete co-localization of the pThr-Pro signal and TaSP only in cells in interphase, pointing towards a cell cycle-dependent event. Immunostainings of isolated, non-permeabilized schizonts confirmed the presence of the pThr-Pro epitope on the schizont's surface. Lambda phosphatase treatment abolished the pThr-Pro signal of the schizont, which was reconstituted by the addition of CDK1-cyclin B. Treatment of T. annulata-infected cells with the CDK1 inhibitor purvalanol A resulted in morphological changes characterized by tubulin-rich cell protrusions and an extension of the schizont, and a dose-dependent reduction of BrdU incorporation and Ki67 staining of T. annulata-infected cells, demonstrating a clear impact on the Theileria-dependent proliferation of the bovine host cell. Our data reveal the parasite surface protein TaSP as a target for the host cell kinase CDK1, a major player during cell division. Targeting the uncontrolled proliferation of Theileria-infected cells is a novel and reasonable approach to limit parasite load in order to facilitate a successful cellular immune response against the parasite.

Theileria annulata transformation altered cell surface molecules expression and endocytic function of monocyte-derived dendritic cells

Theileria annulata is a protozoan parasite transmitted by ticks to cattle. The most important processes of T. annulata are the infection and transformation of host monocytes, which promote cell division and generate a neoplastic phenotype. Dendritic cells play an important role in the development of adaptive immune responses against parasites and are traditionally classified into four types. One type of dendritic cell derived from afferent lymph was successfully transformed by T. annulata in vitro in a previous report. However, whether the monocyte-derived dendritic cells could be transformed and how the endocytic function is affected by T. annulata infection were not yet known. Bovine dendritic cells (DCs) derived from blood CD14⁺ monocytes were cocultured with T. annulata sporozoites in vitro. On day 15 post infection, rounded and continuously proliferating cells were observed. The effect of this transformation on cell phenotype was studied using immunostaining and flow cytometry. After transformation, the cells maintained the expression of the DC-specific marker CD11c, but it was downregulated as were the expression of CD11b, CD14 and CD86. In contrast, CD205, CD45 and MHC class Ⅱ molecules were upregulated in transformed cells. The levels of CD172a, CD21, CD40 and CD80 expression were very low in the transformed cells (<1 %). However, the transformed cells maintained high expression levels of MHC Ⅰ (>99 %). In addition, the normal and transformed DCs were cocultured with OVA-FITC antigen to compare the differences of the endocytic functions between these two types of cells. The results revealed that the endocytic functions of MoDCs were significantly inhibited after transformation by T. annulata.

The Complexity of Piroplasms Life Cycles

Although apicomplexan parasites of the group Piroplasmida represent commonly identified global risks to both animals and humans, detailed knowledge of their life cycles is surprisingly limited. Such a discrepancy results from incomplete literature reports, nomenclature disunity and recently, from large numbers of newly described species. This review intends to collate and summarize current knowledge with respect to piroplasm phylogeny. Moreover, it provides a comprehensive view of developmental events of Babesia, Theileria, and Cytauxzoon representative species, focusing on uniform consensus of three consecutive phases: (i) schizogony and merogony, asexual multiplication in blood cells of the vertebrate host; (ii) gamogony, sexual reproduction inside the tick midgut, later followed by invasion of kinetes into the tick internal tissues; and (iii) sporogony, asexual proliferation in tick salivary glands resulting in the formation of sporozoites. However, many fundamental differences in this general consensus occur and this review identifies variables that should be analyzed prior to further development of specific anti-piroplasm strategies, including the attractive targeting of life cycle stages of Babesia or Theileria tick vectors.

Potential Sabotage of Host Cell Physiology by Apicomplexan Parasites for Their Survival Benefits

Plasmodium, Toxoplasma, Cryptosporidium, Babesia, and Theileria are the major apicomplexan parasites affecting humans or animals worldwide. These pathogens represent an excellent example of host manipulators who can overturn host signaling pathways for their survival. They infect different types of host cells and take charge of the host machinery to gain nutrients and prevent itself from host attack. The mechanisms by which these pathogens modulate the host signaling pathways are well studied for Plasmodium, Toxoplasma, Cryptosporidium, and Theileria, except for limited studies on Babesia. Theileria is a unique pathogen taking into account the way it modulates host cell transformation, resulting in its clonal expansion. These parasites majorly modulate similar host signaling pathways, however, the disease outcome and effect is different among them. In this review, we discuss the approaches of these apicomplexan to manipulate the host–parasite clearance pathways during infection, invasion, survival, and egress.

Fatal cases of Theileria annulata infection in calves in Portugal associated with neoplastic-like lymphoid cell proliferation

This study was carried out to investigate fifteen cases of acute lethal infection of calves (<or= 4 months of age) by the protozoan parasite Theileria (T.) annulata in the south of Portugal. Calves developed multifocal to coalescent nodular skin lesions, similar to multicentric malignant lymphoma. Infestation with ticks (genus Hyalomma) was intense. Theileria was seen in blood and lymph node smears, and T. annulata infection was confirmed by isolation of schizont-transformed cells and sequencing of hypervariable region 4 of the 18S rRNA gene. At necropsy, hemorrhagic nodules or nodules with a hemorrhagic halo were seen, particularly in the skin, subcutaneous tissue, skeletal and cardiac muscles, pharynx, trachea and intestinal serosa. Histologically, nodules were formed by large, round, lymphoblastoid neoplastic-like cells. Immunohistochemistry (IHC) identified these cells as mostly CD3 positive T lymphocytes and MAC387 positive macrophages. A marker for B lymphocytes (CD79alphacy) labeled very few cells. T. annulata infected cells in these nodules were also identified by IHC through the use of two monoclonal antibodies (1C7 and 1C12) which are diagnostic for the parasite. It was concluded that the pathological changes observed in the different organs and tissues were caused by proliferation of schizont-infected macrophages, which subsequently stimulate a severe uncontrolled proliferation of uninfected T lymphocytes.

Cytoplasmic sequestration of p53 promotes survival in leukocytes transformed by Theileria

The function of the p53 protein as the central effector molecule of the p53 apoptotic pathway was investigated in a reversible model of epigenetic transformation. The infection of bovine leukocytes by the intracellular protozoan parasite Theileria annulata results in parasite-dependent transformation and proliferation of the host cells. We found p53 to be largely localized in the host cell cytoplasm and associated with the parasite membrane of isolated schizonts. Curing infected cells of the parasite with the theilericidal drug buparvaquone resulted in a time-dependent translocation of p53 into the host cell nucleus and the upregulation of the proapoptotic Bax and Apaf-1 and the downregulation of the anti-apoptotic Bcl-2 proteins. Although buparvaquone treatment led to apoptosis of the host cell, inhibition of either p53 or Bax significantly reduced buparvaquone-induced apoptosis of the transformed cells. Thus, the p53 apoptotic pathway of host cells is not induced by infection and transformation with Theileria by a mechanism involving cytoplasmic sequestration of p53. The close association of host cell p53 with the parasite membrane implies that the parasite either interacts directly with p53 or mediates cytoplasmic sequestration of p53 by interacting with other host cell proteins regulating p53 localization.

Evolution and diversity of secretome genes in the apicomplexan parasite Theileria annulata

Background

Little is known about how apicomplexan parasites have evolved to infect different host species and cell types. Theileria annulata and Theileria parva invade and transform bovine leukocytes but each species favours a different host cell lineage. Parasite-encoded proteins secreted from the intracellular macroschizont stage within the leukocyte represent a critical interface between host and pathogen systems. Genome sequencing has revealed that several Theileria-specific gene families encoding secreted proteins are positively selected at the inter-species level, indicating diversification between the species. We extend this analysis to the intra-species level, focusing on allelic diversity of two major secretome families. These families represent a well-characterised group of genes implicated in control of the host cell phenotype and a gene family of unknown function. To gain further insight into their evolution and function, this study investigates whether representative genes of these two families are diversifying or constrained within the T. annulata population.

Results

Strong evidence is provided that the sub-telomerically encoded SVSP family and the host-nucleus targeted TashAT family have evolved under contrasting pressures within natural T. annulata populations. SVSP genes were found to possess atypical codon usage and be evolving neutrally, with high levels of nucleotide substitutions and multiple indels. No evidence of geographical sub-structuring of allelic sequences was found. In contrast, TashAT family genes, implicated in control of host cell gene expression, are strongly conserved at the protein level and geographically sub-structured allelic sequences were identified among Tunisian and Turkish isolates. Although different copy numbers of DNA binding motifs were identified in alleles of TashAT proteins, motif periodicity was strongly maintained, implying conserved functional activity of these sites.

Conclusions

This analysis provides evidence that two distinct secretome genes families have evolved under contrasting selective pressures. The data supports current hypotheses regarding the biological role of TashAT family proteins in the management of host cell phenotype that may have evolved to allow adaptation of T. annulata to a specific host cell lineage. We provide new evidence of extensive allelic diversity in representative members of the enigmatic SVSP gene family, which supports a putative role for the encoded products in subversion of the host immune response.

Modulation of NF-kappaB activation in Theileria annulata-infected cloned cell lines is associated with detection of parasite-dependent IKK signalosomes and disruption of the actin cytoskeleton

Apicomplexan parasites within the genus Theileria have the ability to induce continuous proliferation and prevent apoptosis of the infected bovine leukocyte. Protection against apoptosis involves constitutive activation of the bovine transcription factor NF-kappaB in a parasite-dependent manner. Activation of NF-kappaB is thought to involve recruitment of IKK signalosomes at the surface of the macroschizont stage of the parasite, and it has been postulated that additional host proteins with adaptor or scaffolding function may be involved in signalosome formation. In this study two clonal cell lines were identified that show marked differences in the level of activated NF-kappaB. Further characterization of these lines demonstrated that elevated levels of activated NF-kappaB correlated with increased resistance to cell death and detection of parasite-associated IKK signalosomes, supporting results of our previous studies. Evidence was also provided for the existence of host- and parasite-dependent NF-kappaB activation pathways that are influenced by the architecture of the actin cytoskeleton. Despite this influence, it appears that the primary event required for formation of the parasite-dependent IKK signalosome is likely to be an interaction between a signalosome component and a parasite-encoded surface ligand.

Quantitative analysis of cytokine mRNA expression and protozoan DNA load in Theileria parva-infected cattle

Theileria parva (T. parva) causes a highly serious bovine disease called East Coast fever (ECF), which is characterized by pyrexia, dyspnea and cachexia and is of great economic importance in African countries. We hypothesize that the clinical symptoms of ECF could be explained by a cytokine dysregulation. In this study, we investigated the relationship between T. parva DNA load and expression levels of cytokine mRNAs in leukocytes from experimentally infected calves by quantitative PCR. The p104 gene, which encodes the T. parva 104 kDa microneme-rhoptry protein, was detected in cattle blood from day 10 after T. parva-infected tick infestation, and the protozoan DNA load was increased together with severity of disease. The mRNA expressions of pro-inflammatory cytokines, such as interleukin (IL)-1beta and IL-6, were up-regulated with protozoan DNA load increasing. In addition, the level of a type-2 cytokine (IL-10) transcript was also increased during the acute phase. In contrast, the down-regulation or no detectable levels of the expression of type-1 cytokines, such as IL-2 and interferon (IFN)-gamma were observed in T. parva-infected animals. Thus, our observations indicated that high protozoan load and resulting intense inflammatory responses might be involved in the severity of clinical signs observed in T. parva-infection.

Theileria parva infection in calves causes massive lymphocyte death in the thymus, spleen and lymph nodes without initial proliferation

In a study of trends and magnitudes of lymphocytes proliferation, destruction or apoptosis eleven 3-month-old healthy calves were experimentally infected with the protozoan parasite Theileria parva, which is reported to cause lymphocyte proliferation. Four control calves were not infected. Infected and non-infected calves were sacrificed on days 9, 12, 16, 19, 23, 24 and 25 to examine lymphoid tissue changes and lymphocyte proliferation, apoptosis or necrosis in the thymus, spleen and lymph nodes. All infected calves developed severe East Coast fever, with enlargement of lymph nodes, dyspnoea, high fever and pulmonary oedema. Lymphocyte proliferation was not observed in lymph nodes, thymus and spleen; instead there were massive deaths of lymphocytes and other cells. The terminal severe disease caused massive lymphoid parenchyma coagulation terminating with caseation, organs and cells being undeterminable histologically. Tissues surrounding the lymph nodes were oedematous. Lymph node and thymus parenchyma were caseated and cortices and medulla indistinguishable because of severe lymphocyte and accessory cell deaths. The lymph node fibrous reticular stroma was necrotic and caseated. Lymphoid follicles in lymph nodes degenerated and lacked germinal centres. Lymph nodes, spleen and thymus were grossly enlarged, hardened, potato or cheese like, but microscopically very hypocellular and in the terminal disease acellular because of massive lymphocytes destruction. In the thymus there was extensive thymocyte and epithelioid cell necrosis and loss of distinction between cortex and medulla. The spleen white and red pulps were indistinguishable because of extensive lymphoid cell necrosis. The white pulp degenerated more than the red pulp. The massive lymphocyte deaths in the lymph nodes, thymus and spleen, without lymphocyte proliferation in this T. parva infection in calves leads to a conclusion that this parasite is lympho-destructive and lympho-degenerative in vivo rather than lympho-proliferative.

Molecular characterization of a Theileria lestoquardi gene encoding for immunogenic protein splice variants

A Theileria lestoquardi schizont cDNA library was screened using sera collected from sheep recovering from a natural malignant theileriosis infection. An immunogenic clone (clone-5) was isolated and its full sequence was obtained using rapid amplification of cDNA ends polymerase chain reaction (PCR) technique. PCR experiments and sequencing demonstrated the presence of two transcript forms of the gene, resulting from splicing variation at the single intron found in the gene. Both gene products, clone-5 long and clone-5 short variants with calculated molecular weights of 99.9 and 72.7 kDa, respectively, were expressed in a T. lestoquardi-infected cell line. BLAST searches suggested the presence of homologues of the gene in both the Theileria parva and Theileria annulata genomes, with identities of 53 and 62% on the DNA level, respectively. The intron was preserved in size, sequence, and location within the gene in these parasites. Analysis of the subcellular localization of the clone-5 proteins showed a predominant parasite membrane association in T. lestoquardi-infected cells. Both recombinantly produced forms were found to be reactive with sera from infected animals. Bioinformatic analyses were employed to address the possible function of the gene products in the biology of T. lestoquardi.

The kinetics of Theileria parva infection and lymphocyte transformation in vitro

Theileriaparva is an intracellular protozoan parasite that causes a fatal lymphoproliferative disease of cattle known as East Coast Fever. The parasite infects host lymphocytes causing their transformation and uncontrolled proliferation. Infiltration of major organs with parasitized lymphoblasts results in most cases in death within 3 weeks. Although both T and B lymphocytes are susceptible to infection, the majority of cell lines arising from infection of peripheral blood mononuclear cells in vitro are of T cell lineage. To explore the basis of this phenotypic bias we have followed the very early stages of parasite development in vitro at the single cell level. Peripheral blood mononuclear cells were infected and stained for both surface phenotype and intracellular parasite antigen and analysed by flow cytometry. Although the parasite antigen was detected intracellularly as early as 6h p.i., our data indicate that parasite infection does not lead to cell transformation in all instances. Rather, specific cell types appear to undergo selection very early after infection and expansion of particular cell subsets results in survival and growth of only a small proportion of the cells originally parasitized.

Alteration of host cell phenotype by Theileria annulata and Theileria parva: mining for manipulators in the parasite genomes

The apicomplexan parasites Theileria annulata and Theileria parva cause severe lymphoproliferative disorders in cattle. Disease pathogenesis is linked to the ability of the parasite to transform the infected host cell (leukocyte) and induce uncontrolled proliferation. It is known that transformation involves parasite dependent perturbation of leukocyte signal transduction pathways that regulate apoptosis, division and gene expression, and there is evidence for the translocation of Theileria DNA binding proteins to the host cell nucleus. However, the parasite factors responsible for the inhibition of host cell apoptosis, or induction of host cell proliferation are unknown. The recent derivation of the complete genome sequence for both T. annulata and T. parva has provided a wealth of information that can be searched to identify molecules with the potential to subvert host cell regulatory pathways. This review summarizes current knowledge of the mechanisms used by Theileria parasites to transform the host cell, and highlights recent work that has mined the Theileria genomes to identify candidate manipulators of host cell phenotype.

Molecular approaches to elucidating innate and acquired immune responses to Babesia bovis, a protozoan parasite that causes persistent infection

For many vector-transmitted protozoal parasites, immunological control of acute infection leads to a state of persistent infection during which parasitemias may cycle unnoticed in infected but otherwise clinically healthy animals. Achieving persistent infection is a strategy that favors parasitism, since both host and, therefore, parasite survive, and endemically infected animal populations provide a reservoir of parasites continually available for subsequent transmission. Examples of the major economically important protozoan pathogens that cause persistent infection in mammals include the related Theileria and Babesia parasites as well as Trypanosoma species. Control of acute infection and maintenance of clinical immunity against subsequent infection are determined by the interplay of innate and acquired immune responses. This review will focus on approaches taken to gain an understanding of the molecular basis for innate and acquired immunity against the hemoprotozoan parasite of cattle, Babesia bovis. Knowledge of mechanisms used by the parasite to survive within infected cattle from acute to persistent infection combined with definition of the correlates of protective immunity in cattle should be applicable to designing effective vaccines.