Infection of bovine monocyte/macrophage populations with Theileria annulata and Theileria parva

TurboID mapping reveals the exportome of secreted intrinsically disordered proteins in the transforming parasite Theileria annulata

Theileria annulata is a tick-transmitted apicomplexan parasite that gained the unique ability among parasitic eukaryotes to transform its host cell, inducing a fatal cancer-like disease in cattle. Understanding the mechanistic interplay between the host cell and malignant Theileria species that drives this transformation requires the identification of responsible parasite effector proteins. In this study, we used TurboID-based proximity labeling, which unbiasedly identified secreted parasite proteins within host cell compartments. By fusing TurboID to nuclear export or localization signals, we biotinylated proteins in the vicinity of the ligase enzyme in the nucleus or cytoplasm of infected macrophages, followed by mass spectrometry analysis. Our approach revealed with high confidence nine nuclear and four cytosolic candidate parasite proteins within the host cell compartments, eight of which had no orthologs in non-transforming T. orientalis. Strikingly, all eight of these proteins are predicted to be highly intrinsically disordered proteins. We discovered a novel tandem arrayed protein family, nuclear intrinsically disordered proteins (NIDP) 1-4, featuring diverse functions predicted by conserved protein domains. Particularly, NIDP2 exhibited a biphasic host cell-cycle-dependent localization, interacting with the EB1/CD2AP/CLASP1 parasite membrane complex at the schizont surface and the tumor suppressor stromal antigen 2 (STAG2), a cohesion complex subunit, in the host nucleus. In addition to STAG2, numerous NIDP2-associated host nuclear proteins implicated in various cancers were identified, shedding light on the potential role of the T. annulata exported protein family NIDP in host cell transformation and cancer-related pathways.IMPORTANCETurboID proximity labeling was used to identify secreted proteins of Theileria annulata, an apicomplexan parasite responsible for a fatal, proliferative disorder in cattle that represents a significant socio-economic burden in North Africa, central Asia, and India. Our investigation has provided important insights into the unique host-parasite interaction, revealing secreted parasite proteins characterized by intrinsically disordered protein structures. Remarkably, these proteins are conspicuously absent in non-transforming Theileria species, strongly suggesting their central role in the transformative processes within host cells. Our study identified a novel tandem arrayed protein family, with nuclear intrinsically disordered protein 2 emerging as a central player interacting with established tumor genes. Significantly, this work represents the first unbiased screening for exported proteins in Theileria and contributes essential insights into the molecular intricacies behind the malignant transformation of immune cells.

Susceptibility to disease (tropical theileriosis) is associated with differential expression of host genes that possess motifs recognised by a pathogen DNA binding protein

Background

Knowledge of factors that influence the outcome of infection are crucial for determining the risk of severe disease and requires the characterisation of pathogen-host interactions that have evolved to confer variable susceptibility to infection. Cattle infected by Theileria annulata show a wide range in disease severity. Native (Bos indicus) Sahiwal cattle are tolerant to infection, whereas exotic (Bos taurus) Holstein cattle are susceptible to acute disease.

Methodology/Principal findings

We used RNA-seq to assess whether Theileria infected cell lines from Sahiwal cattle display a different transcriptome profile compared to Holstein and screened for altered expression of parasite factors that could generate differences in host cell gene expression.

Significant differences (<0.1 FDR) in the expression level of a large number (2211) of bovine genes were identified, with enrichment of genes associated with Type I IFN, cholesterol biosynthesis, oncogenesis and parasite infection. A screen for parasite factors found limited evidence for differential expression. However, the number and location of DNA motifs bound by the TashAT2 factor (TA20095) were found to differ between the genomes of B. indicus vs. B. taurus, and divergent motif patterns were identified in infection-associated genes differentially expressed between Sahiwal and Holstein infected cells.

Conclusions/Significance

We conclude that divergent pathogen-host molecular interactions that influence chromatin architecture of the infected cell are a major determinant in the generation of gene expression differences linked to disease susceptibility.

Immune Response to Tick-Borne Hemoparasites: Host Adaptive Immune Response Mechanisms as Potential Targets for Therapies and Vaccines

Tick-transmitted pathogens cause infectious diseases in both humans and animals. Different types of adaptive immune mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen antigens or indirectly through soluble factors, such as cytokines and/or chemokines, secreted by host cells as response. Adaptive immunity effectors, such as antibody secretion and cytotoxic and/or T helper cell responses, are mainly involved in the late and long-lasting protective immune response. Proteins and/or epitopes derived from pathogens and tick vectors have been isolated and characterized for the immune response induced in different hosts. This review was focused on the interactions between tick-borne pathogenic hemoparasites and different host effector mechanisms of T- and/or B cell-mediated adaptive immunity, describing the efforts to define immunodominant proteins or epitopes for vaccine development and/or immunotherapeutic purposes. A better understanding of these mechanisms of host immunity could lead to the assessment of possible new immunotherapies for these pathogens as well as to the prediction of possible new candidate vaccine antigens.

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 Pathology of Pathogenic Theileriosis in African Wild Artiodactyls

The published literature on schizont-"transforming," or pathogenic theileriosis, in African wild artiodactyls is dated and based on limited information. Here the authors review the taxonomy, diagnosis, epidemiology, hematology, pathology, and aspects of control in various species. Molecular studies based on 18S and 16S rRNA gene sequences have shown that African wild artiodactyls are commonly infected with diverse Theileria spp., as well as nontheilerial hemoprotozoa and rickettsia-like bacteria, and coinfections with pathogenic and nonpathogenic Theileria species are often recorded. Although theileriosis is still confusingly referred to as cytauxzoonosis in many species, the validity of a separate Cytauxzoon genus in artiodactyls is debated. The epidemiology of theileriosis is complex; the likelihood of fatal disease depends on the interplay of parasite, vertebrate host, tick vector, and environmental factors. Roan calves (Hippotragus equinus) and stressed animals of all host species are more susceptible to fatal theileriosis. Even though regenerative anemia is common, peripheral blood piroplasm parasitemia does not correlate with disease severity. Other than anemia, common macroscopic lesions include icterus, hemorrhages (mucosal, serosal, and tissue), fluid effusions into body cavities, lung edema, and variably sized raised cream-colored foci of leukocyte infiltration in multiple organs. Histopathologic findings include vasocentric hyperproliferation and lysis of atypical leukocytes with associated intracellular schizonts, parenchymal necrosis, hemorrhage, thromboembolism, and edema. Immunophenotyping is required to establish the identity of the schizont-transformed leukocytes in wild ungulates. Throughout the review, we propose avenues for future research by comparing existing knowledge on selected aspects of theileriosis in domestic livestock with that in African wild artiodactyls.

Molecular identification of protozoal and bacterial organisms in domestic animals and their infesting ticks from north-eastern Algeria

A molecular survey was undertaken to determine the presence of protozoal and bacterial organisms in 120 ticks and 87 blood samples collected from mammals in north-eastern Algeria. Eight tick species were morphologically identified including 70 Rhipicephalus (Boophilus) annulatus, 23 Rhipicephalus bursa, five Rhipicephalus sanguineus sensu lato, 11 Hyalomma impeltatum, five Hyalomma scupense, two Hyalommma marginatum, one Hyalomma anatolicum and three Ixodes ricinus. Quantitative PCR screening of the ticks showed that Theileria annulata, "Candidatus Ehrlichia urmitei", Theileria buffeli and Anaplasma platys were detected in Rh. annulatus. Rickettsia massiliae and Anaplasma ovis were detected in Rh. sanguineus s.l. and Rh. bursa. Rickettsia aeschlimannii was detected in Hy. marginatum, Hy. scupense and Hy. impeltatum. Finally, "Candidatus Rickettsia barbariae" was detected in Rh. bursa. In the screening blood samples, Theileria equi, T.annulata, T. buffeli, Babesia bovis, Anaplasma marginale, A. ovis and Borrelia spp. were detected in cattle. Theileria ovis, T. annulata, and A. ovis were detected in sheep. In addition, A. ovis and T. equi were detected in goats and equidea respectively. In this study, T. equi and "Candidatus Rickettsia barbariae" were identified for the first time in Algeria as well as potential new species of Ehrlichia and Anaplasma. Although molecular detection does not indicate vector/reservoir competence when investigating ticks removed from animals, this study expands the knowledge of the microorganisms detected in ticks in north-east of Algeria.

Theileria annulata Cyclophilin1 (TaCyp1) Interacts With Host Cell MED21

Host cells infected by Theileria annulata schizonts show the character of permanent proliferation in vitro, also named transformation. To explore the molecular mechanism a T. annulata Cyp1 (TaCyp1) protein potentially involved in regulating cell transformation was used as bait to screen for its interacting proteins by yeast-two-hybrid assay. Additional GST-pull down experiments confirmed that only MED21 specifically interacted with TaCyp1. Moreover, the distribution of TaCyp1 around T. annulata schizonts facilitated interaction with host cell MED21. As a component of mediator complex, MED21 is normally involved in regulating the transcription of nearly all RNA polymerase II-dependent genes. Therefore, to explore its influence on NF-κB signaling MED21 RNA interference and parasite killing with BW720c treatment were performed. Knock down of MED21 resulted in a significant decrease in NF-κB1/2 mRNA expressions, but no significant change in P105, P52 levels, nor detectable alteration in levels of phosphorylated IκBα/β. By contrast, BW720c treatment induced an obvious decrease in the phosphorylation status of P52 and IκBα/β, but no obvious change in that of P105. This suggests that BW720c-induced parasite death had a significant negative influence on NF-κB signaling, whereas knock down of MED21 had no obvious effect on NF-κB signaling. Characterization of TaCyp1 provides information on the function of parasite cyclophilins and leads to a better understanding of the interactions between T. annulata and its host leukocytes.

Exploring the TLR and NLR signaling pathway relevant molecules induced by the Theileria annulata infection in calves

Theileria annulata is the pathogen of bovine tropical theileriosis. It is extremely harmful to the cattle industry, with huge economic losses. The toll-like receptor (TLR) and NOD-like receptor (NLR) signaling pathways are crucial for resistance to infection of the protozoa, such as Plasmodium falciparum, Toxoplasma gondii, and Trypanosoma cruzi. However, the role of these immune-related pathways is unclear during T. annulata infection. In the present study, peripheral blood mononuclear cells and serum were separated from blood samples of calves infected with homogenized tick supernatants carrying T. annulata sporozoites at 12 h, 24 h, 36 h, 48 h, 72 h, 96 h, 120 h, 144 h and 168 h postinoculation. The Custom RT² Profiler PCR Array was used to explore the mRNA levels of 42 TLR and NLR signaling pathway relevant genes. The TLR1, TLR6, TLR10, NLRP1, and MyD88 genes and their downstream signaling molecules significantly differed after the T. annulata infection in comparison with that of preinfection from 72 h to 168 h postinoculation. The serum concentrations of IL-6, IL-1β, and TNFα were significantly increased at 96 h and 168 h postinfection. These findings provided novel information to help determine the mechanisms of TLR and NLR signaling pathway involvement in protection against T. annulata infection.

The secreted Theileria annulata Ta9 protein contributes to activation of the AP-1 transcription factor

Theileria annulata is an obligate intracellular protozoan parasite of the phylum Apicomplexa. Theileria sporozoites invade bovine leukocytes and develop into a multinucleate syncytial macroschizont that causes uncontrolled proliferation and dissemination of infected and transformed leukocytes. Activator protein 1 (AP-1) is a transcription factor driving expression of genes involved in proliferation and dissemination and is therefore a key player in Theileria-induced leukocytes transformation. Ta9 possesses a signal peptide allowing it to be secreted into the infected leukocyte cytosol and be presented to CD8 T cells in the context of MHC class I. First, we confirmed that Ta9 is secreted into the infected leukocyte cytosol, and then we generated truncated versions of GFP-tagged Ta9 and tested their ability to activate AP-1 in non-infected HEK293T human kidney embryo cells. The ability to activate AP-1-driven transcription was found to reside in the C-terminal 100 amino acids of Ta9 distant to the N-terminally located epitopes recognised by CD8+ T cells. Secreted Ta9 has therefore, not only the ability to stimulate CD8+ T cells, but also the potential to activate AP-1-driven transcription and contribute to T. annulata-induced leukocyte transformation.

Screening and identification of host proteins interacting with Theileria annulata cysteine proteinase (TaCP) by yeast-two-hybrid system

BACKGROUND

Theileria annulata can infect monocytes/macrophages and B lymphocytes and causes severe lymphoproliferative disease in ruminants. Meanwhile, infection by T. annulata leads to the permanent proliferation of cell population through regulating signaling pathways of host cells. Cysteine proteinases (CPs) are one kind of protein hydrolase and usually play critical roles in parasite virulence, host invasion, nutrition and host immune response. However, the biological function of T. annulata CP (TaCP) is still unclear. In this study, a yeast-two-hybrid assay was performed to screen host proteins interacting with TaCP, to provide information to help our understanding of the molecular mechanisms between T. annulata and host cells.

METHODS

The cDNA from purified bovine B cells was inserted into pGADT7-SfiI vector (pGADT7-SfiI-BcDNA, Prey plasmid) for constructing the yeast two-hybrid cDNA library. TaCP was cloned into the pGBKT7 vector (pGBKT7-TaCP) and was considered as bait plasmid after evaluating the expression, auto-activation and toxicity tests in the yeast strain Y2HGold. The yeast two-hybrid screening was carried out via co-transforming bait and prey plasmids into yeast strain Y2HGold. Sequences of positive preys were analyzed using BLAST, Gene Ontology, UniProt and STRING.

RESULTS

Two host proteins, CRBN (Bos taurus cereblon transcript variant X2) and Ppp4C (Bos indicus protein phosphatase 4 catalytic subunit) were identified to interact with TaCP. The results of functional analysis showed that the two proteins were involved in many cellular processes, such as ubiquitylation regulation, microtubule organization, DNA repair, cell apoptosis and maturation of spliceosomal snRNPs.

CONCLUSIONS

This study is the first to screen the host proteins of bovine B cells interacting with TaCP, and 2 proteins, CRBN and Ppp4C, were identified using yeast two-hybrid technique. The results of functional analysis suggest that the two proteins are involved in many cellular processes, such as ubiquitylation regulating, microtubule organization, DNA repair, cell apoptosis and maturation of spliceosomal snRNPs. The interaction with CRBN and Ppp4C indicate that TaCP possibly is involved in regulating signaling pathways and cell proliferation, which is helpful for understanding the interaction between T. annulata and host cells.

The Microtubule-Stabilizing Protein CLASP1 Associates with the Theileria annulata Schizont Surface via Its Kinetochore-Binding Domain

T. annulata, the only eukaryote known to be capable of transforming another eukaryote, is a widespread parasite of veterinary importance that puts 250 million cattle at risk worldwide and limits livestock development for some of the poorest people in the world. Crucial to the pathology of Theileria is its ability to interact with host microtubules and the mitotic spindle of the infected cell. This study builds on our previous work in investigating the host and parasite molecules involved in mediating this interaction. Because it is not possible to genetically manipulate Theileria schizonts, identifying protein interaction partners is critical to understanding the function of parasite proteins. By identifying two Theileria surface proteins that are involved in the interaction between CLASP1 and the parasite, we provide important insights into the molecular basis of Theileria persistence within a dividing cell.

Theileria is an apicomplexan parasite whose presence within the cytoplasm of a leukocyte induces cellular transformation and causes uncontrolled proliferation and clonal expansion of the infected cell. The intracellular schizont utilizes the host cell’s own mitotic machinery to ensure its distribution to both daughter cells by associating closely with microtubules (MTs) and incorporating itself within the central spindle. We show that CLASP1, an MT-stabilizing protein that plays important roles in regulating kinetochore-MT attachment and central spindle positioning, is sequestered at the Theileria annulata schizont surface. We used live-cell imaging and immunofluorescence in combination with MT depolymerization assays to demonstrate that CLASP1 binds to the schizont surface in an MT-independent manner throughout the cell cycle and that the recruitment of the related CLASP2 protein to the schizont is MT dependent. By transfecting Theileria-infected cells with a panel of truncation mutants, we found that the kinetochore-binding domain of CLASP1 is necessary and sufficient for parasite localization, revealing that CLASP1 interaction with the parasite occurs independently of EB1. We overexpressed the MT-binding domain of CLASP1 in parasitized cells. This exhibited a dominant negative effect on host MT stability and led to altered parasite size and morphology, emphasizing the importance of proper MT dynamics for Theileria partitioning during host cell division. Using coimmunoprecipitation, we demonstrate that CLASP1 interacts, directly or indirectly, with the schizont membrane protein p104, and we describe for the first time TA03615, a Theileria protein which localizes to the parasite surface, where it has the potential to participate in parasite-host interactions.

IMPORTANCET. annulata, the only eukaryote known to be capable of transforming another eukaryote, is a widespread parasite of veterinary importance that puts 250 million cattle at risk worldwide and limits livestock development for some of the poorest people in the world. Crucial to the pathology of Theileria is its ability to interact with host microtubules and the mitotic spindle of the infected cell. This study builds on our previous work in investigating the host and parasite molecules involved in mediating this interaction. Because it is not possible to genetically manipulate Theileria schizonts, identifying protein interaction partners is critical to understanding the function of parasite proteins. By identifying two Theileria surface proteins that are involved in the interaction between CLASP1 and the parasite, we provide important insights into the molecular basis of Theileria persistence within a dividing cell.

Global gene expression profile of peripheral blood mononuclear cells challenged with Theileria annulata in crossbred and indigenous cattle

Bovine tropical theileriosis is an important haemoprotozoan disease associated with high rates of morbidity and mortality particularly in exotic and crossbred cattle. It is one of the major constraints of the livestock development programmes in India and Southeast Asia. Indigenous cattle (Bos indicus) are reported to be comparatively less affected than exotic and crossbred cattle. However, genetic basis of resistance to tropical theileriosis in indigenous cattle is not well documented. Recent studies incited an idea that differentially expressed genes in exotic and indigenous cattle play significant role in breed specific resistance to tropical theileriosis. The present study was designed to determine the global gene expression profile in peripheral blood mononuclear cells derived from indigenous (Tharparkar) and cross-bred cattle following in vitro infection of T. annulata (Parbhani strain). Two separate microarray experiments were carried out each for cross-bred and Tharparkar cattle. The cross-bred cattle showed 1082 differentially expressed genes (DEGs). Out of total DEGs, 597 genes were down-regulated and 485 were up-regulated. Their fold change varied from 2283.93 to -4816.02. Tharparkar cattle showed 875 differentially expressed genes including 451 down-regulated and 424 up-regulated. The fold change varied from 94.93 to -19.20. A subset of genes was validated by qRT-PCR and results were correlated well with microarray data indicating that microarray results provided an accurate report of transcript level. Functional annotation study of DEGs confirmed their involvement in various pathways including response to oxidative stress, immune system regulation, cell proliferation, cytoskeletal changes, kinases activity and apoptosis. Gene network analysis of these DEGs plays an important role to understand the interaction among genes. It is therefore, hypothesized that the different susceptibility to tropical theileriosis exhibited by indigenous and crossbred cattle is due to breed-specific differences in the dealing of infected cells with other immune cells, which ultimately influence the immune response responded against T. annulata infection.

Lymphocytes and macrophages are infected by Theileria equi, but T cells and B cells are not required to establish infection in vivo

Theileria equi has a biphasic life cycle in horses, with a period of intraleukocyte development followed by patent erythrocytic parasitemia that causes acute and sometimes fatal hemolytic disease. Unlike Theileria spp. that infect cattle (Theileria parva and Theileria annulata), the intraleukocyte stage (schizont) of Theileria equi does not cause uncontrolled host cell proliferation or other significant pathology. Nevertheless, schizont-infected leukocytes are of interest because of their potential to alter host cell function and because immune responses directed against this stage could halt infection and prevent disease. Based on cellular morphology, Theileria equi has been reported to infect lymphocytes in vivo and in vitro, but the specific phenotype of schizont-infected cells has yet to be defined. To resolve this knowledge gap in Theileria equi pathogenesis, peripheral blood mononuclear cells were infected in vitro and the phenotype of infected cells determined using flow cytometry and immunofluorescence microscopy. These experiments demonstrated that the host cell range of Theileria equi was broader than initially reported and included B lymphocytes, T lymphocytes and monocyte/macrophages. To determine if B and T lymphocytes were required to establish infection in vivo, horses affected with severe combined immunodeficiency (SCID), which lack functional B and T lymphocytes, were inoculated with Theileria equi sporozoites. SCID horses developed patent erythrocytic parasitemia, indicating that B and T lymphocytes are not necessary to complete the Theileria equi life cycle in vivo. These findings suggest that the factors mediating Theileria equi leukocyte invasion and intracytoplasmic differentiation are common to several leukocyte subsets and are less restricted than for Theileria annulata and Theileria parva. These data will greatly facilitate future investigation into the relationships between Theileria equi leukocyte tropism and pathogenesis, breed susceptibility, and strain virulence.

The correlations among serum tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and sialic acids with peripheral lymphocytes in bovine tropical theileriosis

The infection with protozoan parasite Theileria annulata induces changes triggering the activation and/or proliferation of the host lymphocytes. In order to find out the possible correlations among peripheral circulatory lymphocytes, cytokine activities and the level of sialic acids, 50 dairy Holstein cattle, naturally infected with T. annulata, were divided into 4 subgroups according to their parasitemia rates (<1%, 1-3%, 3-5% and >5%). Also, ten non-infected cattle were sampled as control group. Blood samples were taken from jugular vein into acid citrate dextrose-containing tubes for measuring hematological parameters and B and T (CD(4) and CD(8)) cell populations and without anticoagulant for TNF-alpha, IFN-gamma and sialic acid concentrations. Remarkable decreases observed in red blood cells (RBCs), white blood cells (WBCs) and packed cell volume (PCV) in infected cattle compared to healthy ones (P < 0.05). Also, with increase in parasitemia rate, total lymphocytes and monocytes alleviated in the diseased groups. By contrast, total neutrohpils and the concentrations of TNF-alpha, IFN-gamma and total sialic acids were significantly elevated (P < 0.05) in infected animals. Accordingly, the circulatory populations of CD(4) and CD(8) T cells and B cells showed a substantial decrease, while a significant increase was observed in T (CD(4) and CD(8)) cells in cattle infected with <1% parasitemia rates. Decreased circulatory T cell population shows the ineffective responses of T cells to the stimulatory cytokines such as IFN-gamma or TNF-alpha. On the other hand, the elevation of cytokines (particularly IFN-gamma) and sialic acids have presumably an inhibitory role on circulatory B cell population in infected cattle. In addition, a high level of sialic acid concentration indicates the probable role of sialic acid to regulate the parasite-host cell adhesion during sporozoites invasion.

The protozoan parasite Theileria annulata alters the differentiation state of the infected macrophage and suppresses musculoaponeurotic fibrosarcoma oncogene (MAF) transcription factors

The tick-borne protozoan parasite Theileria annulata causes a debilitating disease of cattle called Tropical Theileriosis. The parasite predominantly invades bovine macrophages (m phi) and induces host cell transformation by a mechanism that has not been fully elucidated. Infection is associated with loss of characteristic m phi functions and phenotypic markers, indicative of host cell de-differentiation. We have investigated the effect of T. annulata infection on the expression of the m phi differentiation marker c-maf. The up-regulation of c-maf mRNA levels observed during bovine monocyte differentiation to m phi was suppressed by T. annulata infection. Furthermore, mRNA levels for c-maf and the closely related transcription factor mafB were significantly lower in established T. annulata-infected cell-lines than in bovine monocyte-derived m phi. Treatment of T. annulata-infected cells with the theileriacidal drug buparvaquone induced up-regulation of c-maf and mafB, which correlated with altered expression of down-stream target genes, e.g. up-regulation of integrin B7 and down-regulation of IL12A. Furthermore, T. annulata infection is associated with the suppression of the transcription factors, Pu.1 and RUNX1, and colony stimulating factor 1 receptor (CSF1R) which are also involved in the regulation of monocyte/m phi differentiation. We believe these results provide the first direct evidence that T. annulata modulates the host m phi differentiation state, which may diminish the defence capabilities of the infected cell and/or promote cell proliferation. Musculoaponeurotic fibrosarcoma oncogene (MAF) transcription factors play an important role in cell proliferation, differentiation and survival; therefore, regulation of these genes may be a major mechanism employed by T. annulata to survive within the infected m phi.

Review: Innate immunity to tropical theileriosis

The intracellular protozoan parasite Theileria annulata causes a severe, and often fatal, disease of pure and cross-bred cattle in tropical and subtropical countries. The present review refers to the importance of innate immunity as far as it is known to date in this infectious disease. Specifically, macrophages and the mediators produced by these cells are outlined. In addition, the latest findings concerning cattle breed differences in susceptibility to T. annulata infection in relation to macrophage activation are discussed.

Resistance and susceptibility to a protozoan parasite of cattle—Gene expression differences in macrophages from different breeds of cattle

Cattle infected with the tick-borne protozoan, Theileria annulata, usually undergo severe morbidity, and mortality ensues in a high proportion of animals. However, we have shown that a Bos indicus breed, the Sahiwal, which originates in a T. annulata endemic area, is more resistant to the parasite. Although Sahiwals become infected, the breed exhibits fewer clinical signs and recovers from a dose of parasite which is fatal in the Holstein B. taurus breed. The Sahiwals have a significantly lower fever response, and lower levels of parasite than the Holsteins. One unusual feature of this disease is the production of acute phase proteins (APP), indicating that the parasite induces high systemic levels of pro-inflammatory cytokines. In the Holsteins there is prolonged production of the APP, alpha1-glycoprotein, which, in contrast, is only slightly elevated in the Sahiwals. As the parasite infects macrophages (mphi), our hypothesis is that the Sahiwals can control the excessive production of pro-inflammatory cytokines in response to infection, and that this control is expressed at the level of the mphi. We thus reasoned that the genes underlying the observed difference in resistance to tropical theileriosis, might be identified by investigating gene expression differences in mphi from both breeds. It is possible that relevant polymorphisms might in themselves result in gene expression differences, so initially we targeted likely candidates. However, we detected no differences in expression of the pro-inflammatory cytokines, tumour necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) or IL-6, in infected mphi. As it is more likely that polymorphisms in candidate genes influence the expression of other genes involved in interrelated pathways, we undertook a more global approach. We designed a bovine mphi specific cDNA microarray, which contains representatives of 5000 different genes expressed in mphi, and investigated the transcriptional responses of mphi from both breeds in response to a variety of stimuli, including infection with T. annulata. Our results indicate that there are fundamental differences in gene expression in mphi from both breeds in the way they respond to infection, and even in their pre-infection resting state.

Development and validation of a bovine macrophage specific cDNA microarray

Background

The response of macrophages to danger signals is an important early stage in the immune response. Our understanding of this complex event has been furthered by microarray analysis, which allows the simultaneous investigation of the expression of large numbers of genes. However, the microarray resources available to study these events in livestock animals are limited.

Results

Here we report the development of a bovine macrophage specific (BoMP) cDNA microarray. The BoMP microarray contains 5026 sequence elements (printed in duplicate) and numerous controls. The majority of the clones incorporated on the microarray were derived from the BoMP cDNA library generated from bovine myeloid cells subjected to various stimuli, including over 900 sequences unique to the library. Additional clones representing immunologically important genes have been included on the BoMP microarray. The microarray was validated by investigating the response of bovine monocytes to stimulation with interferon-γ and lipopolysaccharide using amplified RNA. At 2 and 16 hours post stimulation 695 genes exhibited statistically significant differential expression, including; 26 sequences unique to the BoMP library, interleukin 6, prion protein and toll-like receptor 4.

Conclusion

A 5 K cDNA microarray has been successfully developed to investigate gene expression in bovine myeloid cells. The BoMP microarray is available from the ARK-Genomics Centre for Functional Genomics in Farm Animals, UK.

The expanding role of microarrays in the investigation of macrophage responses to pathogens

In the last few years, microarray technology has emerged as the method of choice for large-scale gene expression studies. It provides an efficient and rapid method to investigate the entire transcriptome of a cell. No research field has benefited more from microarray technology than the study of the exquisite interplay between pathogens and hosts. Numerous microarray studies have now been published in this field, which have provided insights into the mechanisms of host defence and the tactics employed by pathogens to circumvent these protection strategies. These studies have led to a more comprehensive understanding of the host immune response and identified new avenues of research for potential control strategies against pathogens. In the past, research has concentrated on human and mouse microarrays to investigate host-pathogen interactions, regardless of the host species. This trend is changing with the ever-expanding sequence resources now available for many pathogen and host species, including livestock animals. The use of species-specific microarrays has furthered our understanding of host-pathogen interactions for particular organisms and aided in the annotation of unknown genes. Macrophages play a central role in the host's innate and adaptive immune responses to pathogens. These cells are in the first line of defence and interact with a wide range of pathogens; many of which have evolved strategies to circumvent the macrophage defence mechanisms and survive within these cells. In this report, we review the wealth of studies using microarray technology to investigate the response of macrophages to pathogens. These studies illustrate how microarray technology has expanded our understanding of the dialogue between macrophage and pathogen and provide examples of the benefits and pitfalls of using this technique. Furthermore, we discuss the resources available to use microarray analysis to study the immune response of a non-human, non-rodent species, the cow.

Accelerated recycling of transferrin receptor in Theileria-transformed B cells

We found that phoshatidylinositol-3 kinase (PI3-K) markedly contributes to the increased surface expression of bovine transferrin receptor (TfR) on Theileria-infected lymphocytes. We observed that all aspects of TfR turnover are upregulated in parasitized B cells and we were able to detect TfR colocalizing with EEA1 (early endosome antigen 1) and Rab11 at the ultrastructure level in Theileria-infected B cells. We demonstrated recycling of TfR through Rab5- and Rab11-positive compartments by transfection of dominant negative guanosine diphosphate (GDP)-on mutants of the GTPases. Therefore, in Theileria-transformed B cells constitutive PI3-K activity leads to accelerated TfR recycling through Rab5- and Rab11-positive compartments.

Bos taurus and Bos indicus (Sahiwal) calves respond differently to infection with Theileria annulata and produce markedly different levels of acute phase proteins

Disease-resistant livestock could provide a potentially sustainable and environmentally sound method of controlling tick and tick-borne diseases of livestock in the developing world. Advances in the knowledge and science of genomics open up opportunities to identify selectable genes controlling disease resistance but first, breeds and individuals with distinguishable phenotypes need to be identified. The Bos indicus breed, Sahiwal, has been exploited in dairy breeding programmes, because it is resistant to ticks and has relatively good performance characteristics compared to other indigenous cattle breeds of tropical regions. The analyses reported here show that Sahiwal calves were also more resistant than European Bos taurus (Holstein) dairy breed calves to tick-borne tropical theileriosis (Theileria annulata infection). Following experimental infection with T. annulata sporozoites, a group of Sahiwal calves all survived without treatment, with significantly lower maximum temperatures (P<0.01) and lower rates of parasite multiplication (P<0.05) than a group of Holstein calves, which all had severe responses. Although the Sahiwals became as anaemic as the Holsteins, other measures of pathology, including enlargement of the draining lymph node and the acute phase proteins, alpha1 acid glycoprotein and haptoglobin, were significantly less in the Sahiwals than in the Holsteins (P<0.05). Additionally, the Sahiwals had significantly lower resting levels of alpha1 acid glycoprotein than the Holsteins (P<0.05). Production of a third acute phase proteins, serum amyloid A, had very similar kinetics in both breeds. Acute phase proteins are produced in response to systemic release of the kinds of pro-inflammatory cytokines that are thought to be responsible for the pyrexic, cachectic and anorexic responses characteristic of tropical theileriosis. The prolonged production of alpha1 acid glycoprotein in the Holsteins is indicative of chronic production of circulating pro-inflammatory cytokines. In contrast, Sahiwals appear able to overcome infection with T. annulata as well as limit pathology by preventing the over-stimulation of pathways involving these cytokines.

A Theileria annulata DNA binding protein localized to the host cell nucleus alters the phenotype of a bovine macrophage cell line

The apicomplexan parasite Theileria annulata is the only intracellular eukaryote that is known to induce the proliferation of mammalian cells. However, as the parasite undergoes stage differentiation, host cell proliferation is inhibited, and the leukocyte is eventually destroyed. We have isolated a parasite gene (SuAT1) encoding an AT hook DNA binding polypeptide that has a predicted signal peptide, PEST motifs, nuclear localization signals, and domains which indicate interaction with regulatory components of the higher eukaryotic cell cycle. The polypeptide is localized to the nuclei of macroschizont-infected cells and was detected at significant levels in cells that were undergoing parasite stage differentiation. Transfection of an uninfected transformed bovine macrophage cell line, BoMac, demonstrated that SuAT1 can modulate cellular morphology and alter the expression pattern of a cytoskeletal polypeptide in a manner similar to that found during the infection of leukocytes by the parasite. Our findings indicate that Theileria parasite molecules that are transported to the leukocyte nucleus have the potential to modulate the phenotype of infected cells.

Quantitative analysis of pro-inflammatory cytokine mRNA expression in Theileria annulata-infected cell lines derived from resistant and susceptible cattle

The pathogenic mechanisms involved in tropical theileriosis, caused by the tick-borne protozoan parasite Theileria annulata, are unclear. Pathology is associated with the schizont stage of the parasite, which resides within bovine macrophages. Breed-specific differences in pathology have been observed in cattle, several Bos indicus breeds are relatively resistant to tropical theileriosis whilst Bos taurus cattle are highly susceptible. Infected cells express pro-inflammatory cytokines and it has been hypothesized that these cytokines play a major role in the pathology of the disease. Therefore, using quantitative RT-PCR we investigated the expression of the key candidates, interleukin 1 beta (IL-1beta), IL-6 and tumour necrosis factor alpha (TNF-alpha), in T. annulata low passage infected cell lines derived ex vivo from experimental infection of resistant and susceptible cattle. mRNA for each cytokine was detected in all cell lines investigated at levels higher than those observed in resting monocytes. However, the analyses did not identify any breed-specific differences. Therefore, these results are not consistent with the hypothesis that differential regulation of infected cell derived pro-inflammatory cytokines (IL-1beta, IL-6 and TNF-alpha) accounts for the breed-related differences in resistance and susceptibility to T. annulata infection. Other, currently unknown mechanisms may be of greater importance.

The protozoan parasite, Theileria annulata, induces a distinct acute phase protein response in cattle that is associated with pathology

Acute phase proteins (APP) are synthesised in the liver in response to the systemic presence of high levels of pro-inflammatory cytokines. Bacteria are considered to be strong inducers of APP whereas viruses are weak or non-inducers of APP. Very few reports have been published on APP induction by parasites. Here, we report that the tick-borne protozoan parasite of cattle, Theileria annulata, induced an atypical acute phase response in cattle. Following experimental infection, serum amyloid A (SAA) appeared first, followed by a rise in alpha(1) acid glycoprotein (alpha(1)AGP) in all animals, whereas haptoglobin, which is a major APP in cattle, only appeared in some of the animals, and generally at a low level. All three APP only became elevated around or after the appearance of schizonts in draining lymph nodes and after the first observed temperature rise. Increased alpha(1)AGP levels coincided with the appearance of piroplasms. The production of SAA and alpha(1)AGP correlated strongly with each other, and also with some clinical measures of disease severity including the time to fever, development of leucopaenia, parasitaemia and mortality. These results are consistent with the hypothesis that T. annulata causes severe pathology in susceptible cattle by inducing high levels of pro-inflammatory cytokines.

Theileria annulata: attenuation of a schizont-infected cell line by prolonged in vitro culture is not caused by the preferential growth of particular host cell types

Flow cytometry and monoclonal antibodies to bovine leucocyte surface antigens were used to identify the types of host cells that the sporozoites of Theileria annulata infect in cattle, to determine whether virulent schizont-infected cell lines (lines) differed phenotypically from avirulent lines, and to establish whether attenuation in vitro was accompanied by the preferential growth of particular host cell types. The surface antigens of four pairs of T. annulata (Ta) (Hisar) lines derived ex vivo and in vitro, including the virulent ex vivo-derived Ta Hisar S45 line, were consistent with a myeloid origin for all lines, irrespective of their derivation. The profiles of lines derived from cattle inoculated with a virulent line showed that the schizonts liberated from inoculated cells had transferred to myeloid cells. A number of other lines infected with different stocks of T. annulata expressed myeloid markers; a single line expressed CD21, a B cell marker. During prolonged in vitro culture, the parasites in the ex vivo (virulent)- and in vitro (avirulent)-derived Ta Hisar S45 myeloid lines became clonal, as defined by glucose phosphate isomerase (GPI) polymorphism, and the virulent line became attenuated. The two lines retained phenotypic profiles indicative of a myeloid origin but coexpressed some lymphoid antigens (CD2, CD4, CD8), although not CD3. Cloned schizont-infected lines, representing the three parasite GPI isotypes which constituted the virulent line, expressed similar patterns of myeloid and lymphoid markers to the virulent parent line. Some schizont-infected clones failed to establish as lines during the early weeks of culture because the cells died as the parasites differentiated into merozoites at 37 degrees C, the temperature at which schizont-infected cells normally grow exponentially. These results provided no evidence that prolonged culture induces preferential growth or loss of particular host cell types. However, a number of the alterations in host cell surface antigens induced by prolonged culture were shown to be linked to permanent changes in the parasite genome.

The balance between protective immunity and pathogenesis in tropical theileriosis: what we need to know to design effective vaccines for the future

The tick-borne protozoan parasite, Theileria annulata, causes an overwhelming disease in Friesian cattle, imported to improve productivity, in a large area of the world. The parasite invades bovine macrophages and induces aberrant changes which seem pivotal in triggering disease in naïve susceptible animals: parasite infected cells acquire dendritic cell features and over-activate CD4+ and CD8+ T cells. Elevated levels of interferon-gamma (IFN-gamma) are induced and B cells are developmentally arrested in the light zone of germinal centres. Infected macrophages are refractory to the effects of IFN-gamma and indeed flourish in its presence. High levels of pro-inflammatory cytokines, as evinced by high acute phase protein responses, probably also play a role in pathology. However, animals can become immune to further challenge. Cellular immune responses involving macrophages, natural killer cells and CD8+ T cells play a major role in recovery and subsequent maintenance of immunity. The main target for immunity appears to be the parasite infected macrophage, as attenuated cell lines can protect and are used as vaccines. Cloned lines selected for low cytokine production protect with no associated pathological reactions. Theileria annulata causes a relatively mild disease in an indigenous breed of cattle, which is associated with lower acute phase protein responses (controlled by macrophage cytokines). Thus the initial host-parasite interactions must determine the balance between immunity and pathogenesis. New generation vaccines to T. annulata should both induce active immunity and suppress pathology.

Theileria annulata in CD5(+) macrophages and B1 B cells

Theileria parasites infect and transform bovine leukocytes. We have analyzed laboratory-established Theileria sp.-infected leukocyte lines and observed that transformed macrophages express CD5. Low-level expression of CD5 by macrophages was further confirmed on three independent Theileria annulata clinical isolates from Tunisia. Interestingly, the fourth CD5(+) clinical isolate (MB2) was morphologically different, expressed surface immunoglobulin M (IgM) and BoLA class II, and had rearranged Ig light-chain genes. To demonstrate that MB2 did indeed contain CD5(+) B cells, individual clonal lines were obtained by limiting dilution, and CD5 expression and Ig gene rearrangement were confirmed. This suggests that in natural infections T. annulata can invade and transform CD5(+) B cells.

Immunity and vaccine development in the bovine theilerioses

There are three economically important bovine Theileria species: Theileria annulata, which causes tropical theileriosis and occurs across north Africa and most of central Asia; Theileria parva, which causes East Coast fever and is found in East and Central Africa; and Theileria sergenti, which is predominantly a problem in Japan and Korea. Theileria annulata preferentially infects macrophages in vivo. It is controlled largely by means of live, attenuated vaccines, which are produced by prolonged tissue culture of the schizont-infected cells. The immunity induced in animals, which have either recovered from an infection or have been vaccinated (with an attenuated vaccine), is broad, solid and cell mediated. It is considered that the main effector cells are cytostatic macrophages that produce nitric oxide. Subsidiary roles for bovine leucocyte antigen (BoLA)-restricted, transiently appearing, cytotoxic T cells, and possibly also natural killer (NK) cells, have been identified. Cytokines such as tumour necrosis factor alpha (TNF-alpha) may have important roles, particularly in the induction of pathology. Matrix metalloproteinases have been implicated in the metastatic behaviour of schizont-infected cells. The nature of the protective schizont target antigens remains unknown. Attempts to develop a subunit vaccine have focused upon a sporozoite antigen (SPAG-1) and a merozoite antigen (Tams1). Both SPAG-1 and Tams1 have given partial protection using different delivery systems and adjuvants, but further vaccine development will probably require identification of a range of other antigens, especially from the schizont stage. Theileria parva has a tropism for T cells. Vaccination is currently by the 'infection and treatment' method, which involves challenging with a controlled dose of sporozoite stabilate and the simultaneous administration of long-acting tetracyclines. The immunity thus induced is mediated by BoLA-restricted cytotoxic T cells, which recognize polymorphic schizont antigens. These antigens have not been characterized at the molecular level. However, the polymorphic nature of the target antigens underlies the fact that the immunity is very strain specific--a situation that distinguishes T. parva from T. annulata. Interestingly, it is not possible to produce an attenuated vaccine to T. parva, as T. parva requires up to two orders of magnitude more schizonts in order to achieve transfer to the new host. A suggested reason for this is that the macrophage targets of T. annulata are phagocytes and thus the schizont has a natural, efficient route of entry whilst the preferred host of T. parva is the non-phagocytic T cell. Analysis of the cytotoxic T-cell response has revealed evidence of BoLA haplotype dominance plus competition between parasite epitopes. Subunit vaccination using a recombinant sporozoite antigen (p67) has proved very promising, with levels of protection of the order of 70% being achieved. A proportion of the protected calves exhibits complete sterile immunity. Interestingly, the basis for this immunity is not clear, since there is no correlation between the titre of antibodies that inhibit sporozoite penetration of lymphocytes and protection. Similarly, there is no significant T-cell response that distinguishes the protected and susceptible animals. These data are very encouraging, but other components, particularly those derived from the schizont, need to be identified and characterized. The mild Theileria species of Japan and Korea (termed T. sergenti in the literature) cause fever and severe chronic anaemia. The schizont stage of the life cycle is very rare and the host cell type is not known. The pathology is associated with chronic piroplasm infection. Immunity can be induced by immunizing with crude piroplasm extracts. Serological analysis of immune sera reveals that the immunodominant antigen is a polypeptide of 30-33 kDa, which corresponds to the protective T. annulata polypeptide Tams1. (ABSTRACT T

Transformation of leukocytes by Theileria parva and T. annulata

Theileria parva and T. annulata provide intriguing models for the study of parasite-host interactions. Both parasites possess the unique property of being able to transform the cells they infect; T. parva transforms T and B cells, whereas T. annulata affects B cells and monocytes/macrophages. Parasitized cells do not require antigenic stimulation or exogenous growth factors and acquire the ability to proliferate continuously. In vivo, parasitized cells undergo clonal expansion and infiltrate both lymphoid and non-lymphoid tissues of the infected host. Theileria-induced transformation is entirely reversible and is accompanied by the expression of a wide range of different lymphokines and cytokines, some of which may contribute to proliferation or may enhance spread and survival of the parasitized cell in the host. The presence of the parasite in the host-cell cytoplasm modulates the state of activation of a number of signal transduction pathways. This, in turn, leads to the activation of transcription factors, including nuclear factor-kappa B, which appear to be essential for the survival of Theileria-transformed T cells.

Diminished IL-2 responses and alteration of CD2 expression on CD8+ T cells are associated with a lack of cytotoxic T cell responses during Theileria annulata infection

Theileria annulata is a tick-borne protozoan parasite which causes the disease bovine tropical theileriosis. In immunized or drug-treated animals, the pathogenic macroschizont stage of the parasite is destroyed by MHC class I-restricted cytotoxic T lymphocytes (CTL). Here we show that although CD8+ T cells increase greatly in number and display activation markers during an acute infection, they exhibit no killing of infected cells. During the ineffectual response, efferent lymph cells' ability to proliferate to IL-2 drops, coinciding with loss of MoAb binding to CD2 by CD8+ cells. When animals were treated with the anti-parasite drug 'Butalex', IL-2 responses, anti-CD2 antibody binding by CD8+ cells and strong CTL activity were restored within 24 h. The initial activation of CD4+ T cells by parasite-infected cells altering the IL-2 production in the draining lymph node is the likely cause of the failure of CTL responses.

Macrophages behaving badly: infected cells and subversion of immune responses to Theileria annulata

The protozoan parasite Theileria annulata is the causative agent of the tick-borne disease tropical theileriosis, responsible for morbidity and mortality of cattle in many developing countries. Here, John Campbell and Roger Spooner discuss how the parasite might evade immune destruction during an acute primary infection. Theileria annulata macroschizont-infected macrophages act as over-efficient antigen-presenting cells within the infected draining lymph node. Infected cells activate CD4+ and CD8+ T cells abnormally, giving rise to a cascade of cytokine production. This altered immune response does not reject the parasitized cells, and might actively participate in the growth of the developing parasite.

Differences Between B Cell and Macrophage Transformation by the Bovine Parasite, Theileria annulata: A Clonal Approach

Theileria annulata, a tick-transmitted protozoan parasite, infects and transforms cells of the hemopoietic system, particularly those of the B cell and monocyte/macrophage lineages. Here, the effect of infection/transformation on the resulting phenotype was studied using a clonal approach. Three phenotypes of transformed cell lines could be discerned. The first is characterized by surface expression of IgM, CD21, and the B cell epitopes, B-B2 and B-B8, Ig heavy chain gene rearrangement, and mRNA expression. Such lines were obtained from fresh and cultured PBMC and at increased frequency from purified B cells, but never from fetal bone marrow cells. The second phenotype can be distinguished from the first by the absence of Ig heavy chain expression and reduced surface expression of B cell markers (CD21, B-B2, B-B8). Clones with this phenotype were obtained from transformed fetal bone marrow cells only. The third phenotype showed an absence of all of the above B cell markers, including surface IgM, and a lack of Ig heavy chain gene rearrangement. The latter clones could be maintained for several weeks after elimination of T. annulata by BW720c treatment, and they reacquired a macrophage-like phenotype. This implies that parasite-induced dedifferentiation is restricted to monocyte/macrophage, and that B cell markers are indicative of cell lineage progeny. Demonstration of surface IgM on PBMC-derived B cell clones suggests that infection of B cells with T. annulata may be an epigenetic method to immortalize ruminant B cells of a defined Ag specificity.

A stage-specific, parasite-induced, "window" of in vivo interferon-gamma production is associated with pathogenesis in Theileria annulata infection

The tick-borne protozoan parasite Theileria annulata causes tropical theileriosis, a severe leukoproliferative disease of cattle, which naive susceptible animals fail to control. The parasite infects and transforms macrophages, developing in the local draining lymph node. IFN gamma has been shown to block parasite development in newly infected cells, and inhibits the growth of fully differentiated macroschizont stage-infected cells in vitro. However, the parasite has been found to specifically induce IFN gamma production by T cells and appears to flourish in the face of this T cell-derived response in vivo. Here we show that the production of IFN gamma in vivo is tightly controlled by the parasite. Induction of cytokine production by T cells is not initiated until the parasite has developed beyond the IFN gamma sensitive trophozoite stage. Cytokine production is kept high as infected macrophages develop, and IFN gamma appears to play an active role in maintaining the growth of these cells. Once the infection is fully established, IFN gamma is down regulated, avoiding potential inhibitory effects. Thus by controlling T cell IFN gamma production, the parasite induces a "window" of cytokine expression which promotes its own growth, but avoids potential inhibitory effects of the cytokine.

Interferon production by Theileria annulata-transformed cell lines is restricted to the beta family

Theileria are tick-transmitted protozoans causing often fatal diseases in ruminants. Theileria sporozoites immortalize and transform host cells of haematopoietic origin. Transformation is associated with profound functional alterations. For example, bovine cells infected by Theileria annulata or T. parva. constitutively produce interferon (IFN). In this study, the type and family of IFN produced by a panel of T. annulata-transformed cell lines and a T. parva-transformed cell line was investigated, using molecular probes specific for the members of the IFN-alpha, IFN-beta, IFN-gamma and IFN-omega family. T. parva-transformed cells produced IFN-gamma exclusively, whereas T. annulata-infected cells expressed type I IFN only. Analysis of mRNA expression showed that this type I IFN was confined to IFN-beta, regardless of the cellular origin of the transformed cells. When cells were exposed to double-stranded RNA (poly (I:C)) which induces IFN production in other systems, a 10-5,000 fold increase in IFN activity was noted. The amounts of IFN-beta mRNA were increased, but mRNA coding for IFN-alpha, IFN-omega or IFN-gamma was not detected. In contrast, primary macrophages, from which many of the tested lines were derived, expressed IFN-alpha, IFN-beta and IFN-omega mRNA to similar degrees when stimulated by LPS or poly (I:C). Thus, T. annulata appears to constitutively turn on IFN-beta gene transcription while silencing the genes coding for IFN-alpha and IFN-omega.

Generation and functional characterisation of canine bone marrow-derived macrophages

A culture of bone marrow cells from the femurs of canine pups at high concentrations of fetal calf serum under non-adherent conditions allowed the proliferation and differentiation of mononuclear phagocyte lineage cells, as evidenced by morphology and CD14 expression. Cells from other lineages progressively diminished in numbers. Cells collected between 12 and 19 days of culture expressed an array of macrophage activities including ingestion of opsonised erythrocytes, generation of superoxide, up-regulation of procoagulant activity and synthesis of tumour necrosis factor (TNF) upon appropriate stimulation. TNF production was enhanced when the cultures were simultaneously stimulated with canine recombinant, or supernatant-derived, interferon-gamma. In contrast, low levels of inducible nitric oxide (NO) synthase were expressed by only a minority of stimulated macrophages, and nitrite could not be detected in the medium. Therefore, canine macrophages generated by this novel culture system resemble human macrophages in their inefficient and restricted generation of NO upon appropriate stimulation.

Induction of protective immunity to Theileria annulata using two major merozoite surface antigens presented by different delivery systems

Allelic forms (Tams1-1 and Tams1-2) of the major merozoite surface antigen gene of Theileria annulata have recently been expressed in Escherichia coli and in Salmonella typhimurium aroA vaccine strain SL3261. To test the potential of subunit vaccines against T. annulata infection, we immunized four groups of three calves with either recombinant (re-) (Tams1-1 and Tams1-2) proteins or naked DNA encoding these antigens. Group I was immunized intramuscularly with both re-proteins incorporated into immunostimulating complexes (ISCOMs). Group II was inoculated intramuscularly with naked plasmid DNA encoding Tams1-1 and Tams1-2. Groups III and IV received S. typhimurium SL3261 [pSTams1-1][pIP5] and SL3261 [pSTams1-2] [pIP5] subcutaneously and orally, respectively. A final group of three animals (Group V) served as an unimmunized control group. Four weeks after the last immunization all calves were challenged with a T. annulata stabilate generated from blood of an infected animal with 30% piroplasm parasitaemia. All calves vaccinated with ISCOMs proved to be protected from T. annulata infection and had generated antibodies against both re-(Tams1-1 and Tams1-2) at the time of challenge. In two of these animals the antibody had a surface binding profile by IFAT. Two of three calves immunized with naked DNA also proved to be protected, but none of the animals had generated any detectable antibodies against the recombinants. Salmonella-based delivery of the recombinants did not induce any protection; two of six animals died of theileriosis and there was no difference between subcutaneous or oral administration. These preliminary results show that re-(Tams1-1 and/or Tams1-2) may elicit protective immune responses in cattle, depending on the antigen delivery system.

Bovine cells infected in vivo with Theileria annulata express CD11b, the C3bi complement receptor

Bovine cells from cattle infected with Theileria annulata were phenotyped with monoclonal antibodies recognizing bovine leukocyte antigens. Macroschizont-infected, transformed cell lines prepared from peripheral blood mononuclear cells of cattle, infected with sporozoites, were assessed by flow cytometry; parasitized cells in tissues from infected cattle were examined by immunocytochemical techniques. Co-expression of markers for different cell lineages by the cell lines precluded a definite conclusion as to their phenotypic origins. For, while the pattern of leukocyte antigens expressed by these in vivo-derived schizont-infected cells, which included CD11b, was indicative of a myeloid origin, the possibility that they were NK cells could not be excluded. The monoclonal antibody (MAb) IL-A15, which recognizes CD11b, reacted with a high proportion of parasitized cells in sections of tissues from infected cattle at all stages of acute disease. Mononuclear cells infected with parasites at all stages of differentiation, from macroschizont to microschizont, expressed CD11b. Such parasitized cells occurred throughout the lymphoid tissues, being found in the thymus, spleen and lymph nodes, particularly the prescapular node draining the site of infection, the hepatic, mesenteric and precrural nodes, as well as in the reticulo-endothelial tissue of the liver, kidney, lung, abomasum, adrenal and pituitary glands. These observations provided the first evidence for a myeloid origin for the parasitized T. annulata cells found in infected bovine tissues and blood and suggested a mechanism whereby schizonts could transfer from cell to cell during mechanical infection with schizont-infected cells.

The same but different: the biology of Theileria sporozoite entry into bovine cells

Theileria are important tick-transmitted protozoan parasites that infect wild Bovidae and domestic animals throughout much of the world. Much of our understanding of Theileria sporozoite invasion of bovine cells is based on work on T. parva, the causative agent of East Coast fever in cattle throughout east, central and southern Africa. Sporozoite entry involves a defined series of sequential but separable steps that differ in important details from the invasion process in other apicomplexans such as Plasmodium and Toxoplasma. While the morphological features of invasion are fairly well documented, the detailed biology of the individual steps is only now becoming clear. This review summarizes much of this recent work on the biology of sporozoite entry. In particular, recent studies on the role of Ca2+ and cell activation processes in sporozoite entry suggest that the initial sporozoite binding event triggers the mobilization of intrasporozoite Ca2+ and the activation of both kinase and G-protein associated signalling processes in the parasite. These processes in turn regulate the invasive capacity of the sporozoite although the identity of these parasite molecules and how they contribute to the invasion process remain to be determined.

T cell activation by Theileria annulata-infected macrophages correlates with cytokine production

A major feature of the pathology induced by Theileria annulata is acute lymphocytic proliferation, and this study investigates the mechanisms underlying the intrinsic ability of T. annulata-infected monocytes to induce naive autologous T cells to proliferate. Different T. annulata-infected clones expressed different but constant levels of MHC class II, varying from < 1.0 x 10(5) to 1.5 x 10(6) molecules/cell, as measured by saturation binding. However, no correlation was found between the level of MHC class II expression and levels of induced T cell proliferation. Theileria annulata-infected cell lines and clones were assayed for cytokine mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR). The infected cells assayed produced mRNA specific for IL-1 alpha, IL-1 beta, IL-6, IL-10 and tumour necrosis factor-alpha (TNF-alpha), but not IL-2 or IL-4. One clone (clone G) did not produce mRNA for TNF-alpha. The degree of T cell proliferation induced by infected cells was directly correlated with the amount of mRNA produced for the T cell stimulatory cytokines IL-1 alpha and IL-6, as assessed by a semiquantitative technique. In contrast, cells infected with the related parasite T. parva produced mRNA for IL-1 alpha, IL-2, IL-4, IL-10 and interferon-gamma (IFN-gamma). Since T. parva-infected cells also induce naive autologous T cell proliferation, it seems likely that the production of IL-1 alpha by cells infected with either parasite is a major signal for the induction of non-specific T cell proliferation.

Theileria annulata induces abberrant T cell activation in vitro and in vivo

The protozoan parasite of cattle, Theileria annulata, causes a severe lymphoproliferative disease, developing initially in the draining lymph node, which is often fatal in naive animals. Infection of macrophages with T. annulata leads to an augmentation of their antigen-presenting capability in vitro and infected cells can induce proliferation of autologous resting T cells from naive animals. This inappropriate activation of T cells may play an important role in the failure of the host to mount an effective immune response in vivo. To investigate this hypothesis we characterized further the response of T cells from naive cattle to infected cells in vitro, and also examined the development of the immune response in lymph nodes draining the sites of T. annulata infection. Both CD4+ and CD8+ T cells from naive peripheral blood mononuclear cells (PBMC) were induced to proliferate and express the activation markers IL-2R and MHC class II when cultured with infected cells. This effect was seen in both 'naive' and 'memory' T cells, and was dependent upon contact with infected cells. In vitro, infected cells are therefore capable of activating T cells irrespective of their antigen specificity or memory status. In draining lymph nodes, although large numbers of IL-2R+ cells developed following infection, these activated cells were only associated with areas of parasite-induced proliferating cells, and subsequently disappeared from the node. Cells expressing IL-2R were not present in recognized sites for T cell development. Germinal centres were severely affected, losing T cell-dependent zones followed by a total destruction of morphology. T cell function is therefore severely disrupted within draining nodes. This study has shown that parasitized cells supply sufficient signals in vitro to activate T cells irrespective of specificity. T cells also are not stimulated in a conventional manner in vivo, and this may play an important role in preventing an effective immune response from being generated.

Theileria annulata sporozoite targets

Bovine peripheral blood mononuclear cells (PBM) infected in vitro with Theileria annulata sporozoites have previously been characterized as MHC class II+ mature macrophages. The ability of T. annulata sporozoites to infect different subpopulations of MHC class II+ bovine monocytes was investigated. Cells were labelled with monocyte specific monoclonal antibodies (MoAb) and isolated using magnetic cell sorting (MACS). Sporozoites infected both immature and mature monocytes, but more readily infected the mature population. A potential ligand for sporozoite entry is the elastin receptor which is expressed mainly on the immature population of monocytes and not on B cells or T cells. T. annulata sporozoites infected elastin receptor positive and negative cell populations equally well. Infected immature cells lost the expression of elastin receptors and the immature marker, subsequently expressing the mature marker. All monocytes lost the expression of CD14 (the LPS receptor) upon infection with sporozoites. The infection of specific populations and subsequent alterations in phenotype may alter the function of these cells and play an important role in disease pathogenesis.

Phenotypic analysis of bovine leukocyte cell lines infected with Theileria annulata

Six cell lines that were infected with Theileria annulata were compared for expression of a range of surface molecules. Immunofluorescence staining with the panel of monoclonal antibodies formulated for the Second Workshop was analysed by flow cytometry. Four lines generated from bovine peripheral blood mononuclear cells by exposure to sporozoites in vitro and one line generated in vivo from an infected calf were phenotypically similar. Phenotypic analysis of those lines did not demonstrate a monocyte or B cell origin, but indicated they were not derived from T cells. An uncloned line generated in vivo from an infected calf was CD3+ and gamma/delta TCR+. The results indicate that a wider range of host cell types may be infected in vivo than suspected hitherto and that some of the cells may express an abnormal pattern of surface molecules. Both could have profound consequences for the pathogenesis of T. annulata infection.

Tick salivary gland extract and interleukin-2 stimulation enhance susceptibility of lymphocytes to infection by Theileria parva sporozoites

Intracellular parasites show host cell specificity, and precise information on the range of host cells is a prerequisite for the identification of host molecules that account for the specificity and are involved in entry processes. The sporozoite stage of the tick-borne protozoan parasite Theileria parva binds to and enters bovine lymphocytes, but precise information on the susceptibility of other cell types present at the tick attachment site is unavailable. We quantitatively examined the susceptibility of cell types known to be present at the tick attachment site by a previously established in vitro assay. Apart from lymphocytes, sporozoites also bind to and enter macrophages and afferent lymph veiled cells; they do not bind to or enter fibroblasts, granulocytes, or erythrocytes. Sporozoites are not phagocytosed by the macrophages or veiled cells but enter them as they do lymphocytes. Since the tick attachment site is a region of cellular inflammation, we also examined the effects of agents known to be present in this area on lymphocyte susceptibility. Short-term preincubation of lymphocytes with tick salivary gland extract, with compounds that induce lymphocyte proliferation, or with interleukin-2 (IL-2), a cytokine produced by activated lymphocytes, increased host cell susceptibility by between 30 and 60%. The IL-2-induced increase in host cell susceptibility could be prevented by treating the lymphocytes with the monoclonal antibody IL-A 111, which reacts with the bovine IL-2 receptor alpha chain and inhibits IL-2-driven cell proliferation. The changes induced by tick salivary gland extract and IL-2 occurred in less than 90 min. Similarly, peripheral blood mononuclear cells from an animal previously immunized with a nonrelated antigen (trypanosome variant surface glycoprotein) and stimulated in vitro with the same antigen showed increases in host cell susceptibility of between 70 and 125%. In contrast, treatment of lymphocytes with gamma interferon did not induce any increase in host cell susceptibility.

Some characteristics of ovine lymphoid cells infected in vivo by Theileria hirci

A panel of monoclonal antibodies reacting with different subsets of sheep lymphocytes plus a polyclonal rabbit anti-sheep Ig antiserum were used to characterize three Theileria hirci-infected lymphoid cell lines that had been infected and transformed in vivo. In parallel, peripheral blood mononuclear cells of Swedish Landrace sheep were exposed to the same antibodies. Whereas the values obtained for healthy Swedish Landrace sheep peripheral mononuclear cells fell within the range previously described for the sheep, T. hirci-infected lymphoid cells reacted only with monoclonal antibodies specific to major histocompatibility (MHC) class I and class II antigens and to leukocyte common antigen (LCA). The results are discussed in the light of the present knowledge on characteristics of bovine lymphoid cells infected and transformed in vivo and in vitro by the related parasites T. parva and T. annulata. Assumedly, the characteristics of ovine lymphoid cells infected with T. hirci bear likeness to those of bovine cells infected with T. annulata.

Production of interferon by Theileria annulata- and T. parva-infected bovine lymphoid cell lines

Theileria annulata and T. parva-infected lymphoblastoid cells were examined for their capacity to produce interferon (IFN). Supernatants of such cells were tested in biological assay for their antiviral activity. Only T. parva-infected cells of T-cell origin were capable of producing IFN-gamma. Supernatants of some but not all T. annulata-infected cells showed also antiviral activity, which was greatly reduced after exposure to a pH of 2. Northern-blot analysis of the cells using an IFN-gamma cDNA probe confirmed the results obtained for T. parva-infected cells in a biological assay. No IFN-gamma mRNA was detected in T. annulata-infected cells. The importance of IFN for the pathogenesis of theileriosis is discussed.

Mimicry of elastin repetitive motifs by Theileria annulata sporozoite surface antigen

Theileria annulata is an important pathogen of cattle in the tropics. The gene sequence of a sporozoite surface antigen (SPAG-1) is reported. Data is also presented demonstrating that SPAG-1 is synthesised as a large precursor. This antigen, which is a candidate for inclusion in a subunit vaccine, shows a remarkable degree of molecular mimicry to the extracellular matrix protein elastin. It contains both repetitive motifs PGVGV and VGVAPG. Immunofluorescence using a monoclonal antibody against VGVAPG confirmed that this peptide is expressed on sporozoites as predicted. The presence of VGVAPG is particularly interesting since this is the ligand for elastin receptors on a range of cell types, including macrophages/monocytes which are a major class of host target cells. It is proposed that this antigen represents the ligand whereby T. annulata recognises its host cells.