Epidemiology and molecular characterization of Theileria annulata in cattle from central Khyber Pakhtunkhwa, Pakistan

Theileria annulata is a tick-borne hemoprotozoan parasite responsible for tropical theileriosis in the bovine population, which causes substantial economic losses to the livestock sector. The present study has investigated, characterized, and shaped epidemiologic and phylogenetic profiles of T. annulata infection in the cattle population of central Khyber Pakhtunkhwa, Pakistan. A total of 600 blood samples were collected from cattle. Microscopy and PCR (18S rRNA taxonomic marker) assays were performed to detect T. annulata infection in cattle from the study area. The overall relative prevalence rates of T. annulata in the examined cattle population were 12.8% (microscopy) and 23.7% (PCR). District-wise analysis (microscopy/PCR) showed that cattle from district Mardan were found more infected (16.0%/28.0%), as compared to cattle from district Charsadda (13.5%/25.5%) and district Peshawar (9.0%/17.5%). Based on host demographic and ecological parameters analysis, theileriosis was found to be higher in young, female, crossbred, freely grazing, tick-infested, and irregular/no acaricides treated cattle. The univariate logistic analysis showed that host age, tick infestation, acaricides use, and feeding method were significant risk factors (P<0.05) whereas multivariate analysis indicated that host age, gender, tick infestation, acaricidal application, and feeding method were potential risk factors (P<0.05) for tropical theileriosis in the cattle population. Phylogenetic and sequence analysis showed that T. annulata 18S rRNA isolates shared homology and phylogeny with other isolates from Asia and Europe. This study has addressed the epidemiology and phylogeny of T. annulata circulating in bovid in the study area where gaps were still present. These findings will serve as a baseline and will facilitate future large-scale epidemiological investigations on tropical theileriosis in the cattle population at a national level.

Establishment and Expression of Cytokines in a Theileria annulata-Infected Bovine B Cell Line

This study aimed to establish a pure single-cell Theileria annulata-infected B cell line for the assessment of cytokine production in transformed and lipopolysaccharide (LPS)-stimulated cells. Several studies have aimed to identify cell surface markers in T. annulata-transformed cells; however, no information on cytokine production in these cells is available. To investigate the potential of the transformed cells to produce cytokines and their potential responses to antigen-stimulation, we purified mature B cells (CD21) from the whole blood of cattle experimentally infected with the T. annulata Kashi strain by magnetic separation. The purity and specificity of the established cell line was assessed by the identification of specific cell surface markers (CD21, IgM, and WC4) by flow cytometry analysis. The transcript levels of the cytokines IL1A, IL1B, IL2, IL4, IL6, IL8, IL10, IL16, LTA, TGFB1, TNFA, IFNA, and IFNB in transformed, buparvaquone (BW720c)-treated cells, and antigen-stimulated cells were analyzed by quantitative polymerase chain reaction (qPCR) using cDNA from these cells. A T. annulata-infected bovine B cell line was successfully established with a purity of ~98.8% (CD21). IL4 and IL12A were significantly (p < 0.01) upregulated in the transformed cells. In BW720c-treated transformed cells, IL12B, TGFB1, and IFNB were significantly (p < 0.01) upregulated. Notably, no significant (p > 0.05) upregulation of cytokines was observed in LPS-stimulated transformed cells. Moreover, IL1A, IL1B, IL8, and IL16 were significantly (p < 0.01) upregulated in LPS-stimulated B cells. Our data signify the potential use of this cell line for cytokine production, observance of immunoglobulins, and production of an attenuated vaccine against tropical theileriosis.

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.

miR-126-5p by direct targeting of JNK-interacting protein-2 (JIP-2) plays a key role in Theileria-infected macrophage virulence

Theileria annulata is an apicomplexan parasite that infects and transforms bovine macrophages that disseminate throughout the animal causing a leukaemia-like disease called tropical theileriosis. Using deep RNAseq of T. annulata-infected B cells and macrophages we identify a set of microRNAs induced by infection, whose expression diminishes upon loss of the hyper-disseminating phenotype of virulent transformed macrophages. We describe how infection-induced upregulation of miR-126-5p ablates JIP-2 expression to release cytosolic JNK to translocate to the nucleus and trans-activate AP-1-driven transcription of mmp9 to promote tumour dissemination. In non-disseminating attenuated macrophages miR-126-5p levels drop, JIP-2 levels increase, JNK1 is retained in the cytosol leading to decreased c-Jun phosphorylation and dampened AP-1-driven mmp9 transcription. We show that variation in miR-126-5p levels depends on the tyrosine phosphorylation status of AGO2 that is regulated by Grb2-recruitment of PTP1B. In attenuated macrophages Grb2 levels drop resulting in less PTP1B recruitment, greater AGO2 phosphorylation, less miR-126-5p associated with AGO2 and a consequent rise in JIP-2 levels. Changes in miR-126-5p levels therefore, underpin both the virulent hyper-dissemination and the attenuated dissemination of T. annulata-infected macrophages.

PCR diagnosis of tick-borne pathogens in Maharashtra state, India indicates fitness cost associated with carrier infections is greater for crossbreed than native cattle breeds

Tick-borne pathogens (TBP) are responsible for significant economic losses to cattle production, globally. This is particularly true in countries like India where TBP constrain rearing of high yielding Bos taurus, as they show susceptibility to acute tick borne disease (TBD), most notably tropical theileriosis caused by Theileria annulata. This has led to a programme of cross breeding Bos taurus (Holstein-Friesian or Jersey) with native Bos indicus (numerous) breeds to generate cattle that are more resistant to disease. However, the cost to fitness of subclinical carrier infection in crossbreeds relative to native breeds is unknown, but could represent a significant hidden economic cost. In this study, a total of 1052 bovine blood samples, together with associated data on host type, sex and body score, were collected from apparently healthy animals in four different agro-climatic zones of Maharashtra state. Samples were screened by PCR for detection of five major TBPs: T. annulata, T. orientalis, B. bigemina, B. bovis and Anaplasma spp.. The results demonstrated that single and co-infection with TBP are common, and although differences in pathogen spp. prevalence across the climatic zones were detected, simplistic regression models predicted that host type, sex and location are all likely to impact on prevalence of TBP. In order to remove issues with autocorrelation between variables, a subset of the dataset was modelled to assess any impact of TBP infection on body score of crossbreed versus native breed cattle (breed type). The model showed significant association between infection with TBP (particularly apicomplexan parasites) and poorer body condition for crossbreed animals. These findings indicate potential cost of TBP carrier infection on crossbreed productivity. Thus, there is a case for development of strategies for targeted breeding to combine productivity traits with disease resistance, or to prevent transmission of TBP in India for economic benefit.

Engineering attenuated virulence of a Theileria annulata-infected macrophage

Live attenuated vaccines are used to combat tropical theileriosis in North Africa, the Middle East, India, and China. The attenuation process is empirical and occurs only after many months, sometimes years, of in vitro culture of virulent clinical isolates. During this extensive culturing, attenuated lines lose their vaccine potential. To circumvent this we engineered the rapid ablation of the host cell transcription factor c-Jun, and within only 3 weeks the line engineered for loss of c-Jun activation displayed in vitro correlates of attenuation such as loss of adhesion, reduced MMP9 gelatinase activity, and diminished capacity to traverse Matrigel. Specific ablation of a single infected host cell virulence trait (c-Jun) induced a complete failure of Theileria annulata–transformed macrophages to disseminate, whereas virulent macrophages disseminated to the kidneys, spleen, and lungs of Rag2/γC mice. Thus, in this heterologous mouse model loss of c-Jun expression led to ablation of dissemination of T. annulata–infected and transformed macrophages. The generation of Theileria-infected macrophages genetically engineered for ablation of a specific host cell virulence trait now makes possible experimental vaccination of calves to address how loss of macrophage dissemination impacts the disease pathology of tropical theileriosis.

Tropical theileriosis is a leukaemia-like disease of cattle caused by the Apicomplexa parasite Theileria annulata. Live attenuated vaccines are used to control the mortality and morbidity of tropical theileriosis and each endemic country produces its own vaccine by isolating a virulent clinical isolate and then growing the infected and transformed macrophages for many months in the laboratory. With time, virulence is progressively lost, and loss is evaluated from time to time by injecting infected macrophages into calves and monitoring any resulting pathology. If the calves demonstrate clinical symptoms, in vitro culture of vaccine lines continues, and eventually attenuation is achieved after approximately two years. The process is empirical, and with time in culture the infected macrophage lines lose their vaccine potential such that when cattle are injected the immune response to the vaccine can be compromised. To circumvent these problems we engineered the rapid loss of a host macrophage virulence trait and obtained complete attenuation of dissemination of T. annulata–transformed macrophages when tested in an immune-compromised mouse model. This rational, rather than empirical, approach now allows injecting into calves Theileria-infected macrophages engineered for attenuation to evaluate the role of Theileria-infected macrophage dissemination in the pathology of tropical theileriosis.

Population diversity and multiplicity of infection in Theileria annulata

The tick-borne apicomplexan parasite Theileria annulata is endemic in many sub-tropical countries and causes the bovine disease tropical theileriosis. Although the parasite is known to be highly diverse, detailed information is lacking on the genetic structure of natural populations and levels of multiplicity of infection in the cattle host. With the widespread deployment of live attenuated vaccines and the emergence of drug-resistant parasites in the field, it is vital to appreciate the factors which shape genetic diversity of the parasite both within individual hosts and in the wider population. This study addresses these issues and represents an extensive genetic analysis of T. annulata populations in two endemic countries utilising a high-throughput adaptation of a micro- and mini-satellite genotyping system. Parasite material was collected from infected cattle in defined regions of Turkey and Tunisia to allow a variety of analyses to be conducted. All animals (n=305) were found to harbour multiple parasite genotypes and only two isolates shared an identical predominant multi-locus profile. A modelling approach was used to demonstrate that host age, location and vaccination status play a measurable role in determining multiplicity of infection in an individual animal. Age was shown to positively correlate with multiplicity of infection and while positive vaccination status exerted a similar effect, it was shown to be due not simply to the presence of the immunising genotype. Importantly, no direct evidence was found for the immunising genotype spreading or recombining within the local parasite community. Genetic analysis confirmed the tentative conclusion of a previous study that the parasite population appears to be, in general, panmictic. Nevertheless, evidence supporting linkage disequilibrium and a departure from panmixia was uncovered in some localities and a number of explanations for these findings are advanced.

[Use of multiplex PCR for the diagnosis of Theileria annulata and Theileria buffeli]

The species causing theileriosis in cattle in Turkey are Theileria annulata and T. buffeli. While T. buffeli is low in pathogenicity or non-pathogenic , T. annulata is very pathogenic and causes tropical theileriosis with high morbidity and mortality in cattle. In this study, a multiplex PCR was used for a simultaneous diagnosis of these species. Genes for the merozoite surface antigen (Tams 1) and the major piroplasm surface protein (MPSP) were amplified with PCR for T. annulata and T. buffeli, respectively. It was found that both single and mixed infection with T. annulata and T. buffeli could be diagnosed with multiplex PCR.

Evaluation of antioxidant status and oxidative stress in cattle naturally infected with Theileria annulata

To assess the antioxidant status and oxidative stress in bovine theileriosis due to Theileria annulata blood samples were collected from 35 clinically affected cattle referred to Veterinary Teaching Hospital, School of Veterinary Medicine, Urmia University, Urmia, Iran. Complete blood count, piroplasm parasitemia percentage, erythrocyte glutathione peroxidase, superoxide dismutase, catalase and glucose-6-phosphate dehydrogenase activities, malondialdehyde concentration, osmotic fragility test and median corpuscular fragility were determined and the results were compared with those of 50 healthy controls. Of 35 affected cattle, 12 (34.28%) had severe anemia and 23 had mild to moderate anemia and parasitemia varied from 5 to 40%. The activities of erythrocyte glutathione peroxidase, superoxide dismutase and glucose-6-phosphate dehydrogenase were significantly lower (P<0.0001) and the activity of catalase was significantly higher in the affected cattle than in healthy ones (P<0.001). Malondialdehyde concentration in erythrocytes of affected cattle was significantly more than those of healthy cattle (P<0.001). The affected cattle showed increased fragility of erythrocytes, so that median corpuscular fragility (MCF) in affected group was significantly lower than those of healthy group (P<0.0001). Median corpuscular fragility showed a positive correlation with the severity of parasitemia (r=0.81, P<0.0005) and a negative correlation with the activities of GSH-Px (r=-0.78, P<0.0001), SOD (r=-0.71, P<0.0005), catalase (r=-0.53, P<0.018) and G6PD (r=-0.58, P<0.0005). The results of this study suggest that oxidative damage to RBCs may contribute to the pathogenesis of anemia in bovine theileriosis.

Status of Lipid Peroxidation, Some Antioxidant Enzymes and Erythrocytic Fragility of Crossbred Cattle Naturally Infected with Theileria annulata

Erythrocytic lipid peroxidation, activities of some antioxidant enzymes and osmotic fragility of red blood cells was studied in adult (>1 year) crossbred cattle naturally infected with Theileria annulata. Twenty clinically healthy animals (group I) and 15 clinical cases (group II) of tropical theileriosis were selected. Cattle suffering from theileriosis had significantly higher (p<0.01) erythrocytic lipid peroxidation and osmotic fragility. Activities of antioxidant enzymes, viz. glucose-6-phosphate dehydrogenase (G6PD) and glutamate peroxidase (GPx) were also significantly increased (p<0.01) in group II. However, superoxide dismutase and catalase did not show significant changes. The results indicated that infection with theileria led to increased oxidative stress to the animals, and even a significant rise in the activities of antioxidant enzymes. G6PD and GPx could not lower this oxidative stress. However, the increase in the activities of antioxidant enzymes pointed towards the body's defence mechanism against lipid peroxidation during oxidative stress in theileriosis.

Genome of the Host-Cell Transforming Parasite Theileria annulata Compared with T. parva

Theileria annulata and T. parva are closely related protozoan parasites that cause lymphoproliferative diseases of cattle. We sequenced the genome of T. annulata and compared it with that of T. parva to understand the mechanisms underlying transformation and tropism. Despite high conservation of gene sequences and synteny, the analysis reveals unequally expanded gene families and species-specific genes. We also identify divergent families of putative secreted polypeptides that may reduce immune recognition, candidate regulators of host-cell transformation, and a Theileria-specific protein domain [frequently associated in Theileria (FAINT)] present in a large number of secreted proteins.

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.

TashHN, a Theileria annulata encoded protein transported to the host nucleus displays an association with attenuation of parasite differentiation

The intracellular apicomplexan parasite, Theileria annulata, manipulates its bovine host cell by over-riding the cells natural apoptotic response and inducing proliferation of the infected leukocyte. We have recently identified a T. annulata encoded family of polypeptides (TashATs) with characteristics that indicate that they are involved in control of host cell gene expression. Here we present data on another member of this family, TashHN, showing that it is located to the parasite and host cell nucleus. Immunoblot analysis demonstrated that, unlike TashAT2 and 3, TashHN displays three forms, the largest of which is enriched in the host nuclear fraction and appears to be phosphorylated. Northern and 5 prime race analyses identified multiple TashHN RNA species in infected cells that have retained the ability to differentiate. These transcripts showed subtly different kinetics, but all decreased during differentiation to the merozite, and two showed reduced levels prior to down-regulation of the other TashATs. In addition, analyses of multiple cell lines that have become severely attenuated in their potential to differentiate, indicated a substantial increase in TashHN expression, with host nuclear reactivity particularly enhanced.

Proteolytic enzyme activity and attenuation of virulence in Theileria annulata schizont-infected cells

A field isolate of Theileria annulata (Uzbek strain) was obtained from calves infected by Hyalomma anatolicum ticks collected from an endemic region in Uzbekistan. Schizont-infected bovine cells that had been established and propagated in cell culture were examined for attenuation both in vivo, by inoculating cells from various passages into calves, and in vitro for metalloproteinase activity. During serial subcultivation a gradual reduction in virulence and in enzyme activity in cells infected with the Uzbek strain were observed. Complete attenuation of the Uzbek isolate was obtained at about passage 80, and only traces of proteolysis were detected in gelatin substrate gels. In contrast, there was no direct correlation between virulence and enzyme levels in an Israeli strain. While schizonts of the Israeli strain were completely attenuated at passage 80, proteolysis in the substrate gels was detected up to passage 197. Solid immunity was observed in calves immunized with attenuated T. annulata schizonts of the Uzbek strain upon challenge with the homologous H. excavatum sporozoites. For a strain to be used for vaccine production, it appears that animal inoculation still remains the most reliable method to assess the degree of attenuation and protection.

The innate resistance of Kenana cattle to tropical theileriosis (Theileria annulata infection) in the Sudan

A study was carried out to assess the innate resistance of the indigenous Kenana breed of cattle in the Sudan to tropical theileriosis, Theileria annulata infection of cattle. Nine susceptible Kenana calves were obtained from an area free from tropical theileriosis and the vector tick Hyalomma anatolicum anatolicum and were found negative to T. annulata antibodies in the indirect fluorescent antibody test. They were infected by inoculation of 1.0 mL T. annulata sporozoite stabilate. Three Friesian calves were also infected and served as susceptible controls. The percent of schizont parasitosis (Macroschizont Index, MSI) in the Kenana cattle was reduced by 70% compared to the Friesian calves. The percent of piroplasm parasitemia was also significantly lower in the Kenana calves. The rate of white blood cell reduction was significantly greater in the Friesian calves (P < 0.05). These differences were attributed to the high rate of schizont multiplication in the control cattle. Seventy-eight percent (7/9) of the Kenana cattle recovered spontaneously, and only 22% required treatment compared to 100% mortality in the Friesian controls. These differences were attributed to the high rate of schizont multiplication in the control cattle and, on the other hand, ability of the Kenana cattle to limit the MSI, resulting in less severe damage to the lymphoid tissue during the acute phase of the disease.

A dual role for immunosuppressor mechanisms in infection with Theileria annulata: well-regulated suppressor macrophages help in recovery from infection; profound immunosuppression promotes non-healing disease

There is increasing evidence that immune mechanisms are involved in the pathogenesis of many parasitic infections, including infections with the tick-borne protozoan Theileria annulata. The initial stages of tropical theileriosis are characterised by the induction of a non-specific lymphoproliferation by schizont-infected cells which is believed to disrupt antigen recognition and interfere with protective immune responses. This study examined the possibility that cattle do not always succumb to infection because macrophages suppress this non-specific lymphoproliferation. The results provide evidence that lymphoproliferation in cattle may be controlled by two types of suppressor macrophages. The first type occurs in infected cattle and acts via a feedback loop well documented in other parasitic infections. This loop involves macrophages, apparently activated by high levels of gamma interferon produced by proliferating lymphocytes, which suppress lymphocyte proliferation via a prostaglandin-mediated pathway. The properties of a suppressor activity seen in immunised and challenged animals suggested that cattle also possess a type of novel suppressor macrophage recently described in filarial infections. This second type of suppressor macrophage does not seem to act via prostaglandin; its activity appeared to be linked to a suppressor epitope on the sporozoite antigen SPAG-1. Differences in the nature of the schizont-infected cells of the Friesian and Sahiwal calves used in one section of this work, in the in vitro and in vivo lymphoproliferative responses of the two groups of calves and in the behaviour of their suppressor macrophages suggested several reasons why the outcome of Theileria infections differed in the two cattle breeds. This study has extended our knowledge of the pluripotential activities of macrophages in T. annulata infections to include immunosuppression as well as anti-parasite responses and confirmed the view that the outcome of infection with T. annulata, as with many parasitic infections, depends upon the final balance of the protective and pathological properties of the immune system.

Infection and transformation of dendritic cells from bovine afferent lymph by Theileria annulata

Following incubation with sporozoites of the protozoan parasite Theileria annulata, dendritic cells (DC), extracted from bovine afferent lymph, became infected and transformed into large, rounded, continuously proliferating cell lines. Phenotypic analysis of the transformed cells by immunostaining and flow cytometry revealed that they expressed MHC class I and II antigens, the myeloid marker MyD (SIRP alpha) and the bovine WC6 (workshop cluster 6) molecule. Transformed DC cell lines differed from those produced from infection of macrophages and B cells in that some lines expressed CD21 and a proportion of cells continued to express the antigen stained by the mAb CC81, a marker which defines a subpopulation of DC in afferent lymph. Both of the main populations of DC that have been identified in bovine afferent lymph appeared to be equally permissive for infection and transformation with T. annulata. These findings raise the possibility that the transformed proliferating cells characteristic of in vivo infections could be derived from DC as well as macrophages. This could have consequences for understanding the pathogenesis of the disease and for developing methods to manipulate immune responses to eliminate the parasite.

Theileria annulata: virulence and transmission from single and mixed clone infections in cattle

Theoretically, parasite virulence should be higher for faster growing parasites, and higher in mixed infections compared to single-clone infections. Virulence should also be positively correlated to transmission rates. Theileria annulata provides a good model system for studying such hypotheses, as parasite replication causes harm to the host, and there is evidence suggesting that the genetic complexity of an infection might affect its virulence. Two clones of T. annulata were chosen, one fast growing and one slow growing in vitro and these were used to establish cattle infections, either alone, or in a mixed infection. Virulence was measured using lymph node expansion, temperature, and blood parameters as correlates. As predicted, the faster growing clone was found to produce higher virulence. Mixed infections did not show higher virulence than single-clone infections, but interactions within mixed infections resulted in more transmission stage production than seen in either of the single-clone infections. Index Descriptors and Abbreviations. Theileria annulata, Apicomplexa, mixed infections, virulence, growth rates, red blood cell, RBC; packed cell volume, PCV.

Comparative studies on surface phenotypes of Theileria lestoquardi and T. annulata schizont-infected cells

Phenotypes of sheep cell lines infected with Theileria lestoquardi or T. annulata were studied by flow cytometric analysis, following immunolabelling with a panel of monoclonal antibodies reacting to leukocyte differentiation antigens. Cell surface phenotypes of Theileria-infected sheep cell lines derived ex vivo and in vitro were compared, both with each other and with cell lines from cattle undergoing acute T. annulata infection. Besides the non-lineage specific markers CD45, MHC class I and MHC class II, myeloid lineage-associated antigens and B cell-specific markers were expressed in all five different types of line, suggesting that both T. lestoquardi and T. annulata had infected the same cell types in sheep as T. annulata in cattle, notably monocytes/macrophages and B cells. Lineage-specific markers were generally expressed at low frequency and intensity; any differences between the five types of cell lines were quantitative, rather than qualitative. Thus, relative rather than absolute differences in cell preference of sporozoites of T. lestoquardi and T. annulata may contribute to the differences observed in previous studies in the course of the infection of sheep with each of these two parasites and in the infection of cattle with T. annulata.

The Akt/PKB pathway is constitutively activated in Theileria-transformed leucocytes, but does not directly control constitutive NF-kappaB activation

The intracellular protozoan parasites Theileria parva and Theileria annulata transform leucocytes by interfering with host cell signal transduction pathways. They differ from tumour cells, however, in that the transformation process can be entirely reversed by elimination of the parasite from the host cell cytoplasm using a specific parasiticidal drug. We investigated the state of activation of Akt/PKB, a downstream target of PI3-K-generated phosphoinositides, in Theileria-transformed leucocytes. Akt/PKB is constitutively activated in a PI3-K- and parasite-dependent manner, as judged by the specific phosphorylation of key residues, in vitro kinase assays and its cellular distribution. In previous work, we demonstrated that the parasite induces constitutive activation of the transcription factor NF-kappaB, providing protection against spontaneous apoptosis that accompanies transformation. In a number of other systems, a link has been established between the PI3-K-Akt/PKB pathway and NF-kappaB activation, resulting in protection against apoptosis. In Theileria-transformed leucocytes, activation of the NF-kappaB and the PI3-K-Akt/PKB pathways are not directly linked. The PI3-K-Akt/PKB pathway does not contribute to the persistent induction of IkappaBalpha phosphorylation, NF-kappaB DNA-binding or transcriptional activity. We show that the two pathways are downregulated with different kinetics when the parasite is eliminated from the host cell cytoplasm and that NF-kappaB-dependent protection against apoptosis is not dependent on a functional PI3-K-Akt/PKB pathway. We also demonstrate that Akt/PKB contributes, at least in part, to the proliferation of Theileria-transformed T cells.

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.

Proinflammatory cytokine expression by Theileria annulata infected cell lines correlates with the pathology they cause in vivo

Control of Theileria annulata is currently best achieved by the use of live attenuated cell line vaccines. However, the mechanisms underlying attenuation are unclear and there is a need to rapidly produce new cell line vaccines, which could safely and effectively vaccinate cattle against tropical theileriosis. There is increasing evidence to suggest that proinflammatory cytokines produced by T. annulata infected cells play a central role in both pathology and immune evasion. This study aimed to test this hypothesis and to evaluate cytokine expression as a marker of virulence. The pathogenicity and protective efficacy of cloned T. annulata cell lines that expressed different levels of proinflammatory cytokines were compared. In two independent trials using different stocks of T. annulata, cell lines that expressed higher levels of proinflammatory cytokines induced severe reactions, and in some cases death, when used to vaccinate groups of cattle. In contrast, low cytokine expressing lines induced low post-vaccinal reactions. The results clearly demonstrated that cytokine expression by T. annulata infected cells could be used as a marker of virulence and provided strong evidence to support a role for cytokines in the induction of pathology. Both high and low cytokine expressing cell lines protected cattle against heterologous challenge infection, offering the possibility of using cytokine expression to rapidly select new safe, potent vaccines against tropical theileriosis without the need for culture attenuation.

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.

Loss of matrix metalloproteinase 9 activity in Theileria annulata-attenuated cells is at the transcriptional level and is associated with differentially expressed AP-1 species

The schizont stage of the protozoan parasite Theileria annulata reversibly transforms bovine monocytes into an immortalised and metastatic state. We have been studying T. annulata induction of host matrix metalloproteinases (MMP) which are involved in parasite dissemination and pathogenesis. We have observed that prolonged in vitro culture of T. annulata-infected cell lines results in their attenuation and this process is associated with alterations in both host and parasite gene expression. In particular, a loss in bovine MMP expression in later passage cultures suggests that these parasite-induced MMPs are virulence factors. As a means to further our understanding of the attenuation process we examine in detail the parasite-induced differential expression of one particular bovine proteinase, MMP9, in non-attenuated (p58) and attenuated (p158) passage levels of the Ode vaccine line. We show here that MMP9 expression is regulated at the transcriptional level and we suggest that a particular parasite-induced AP-1 recognition transcription factor present in the Ode non-attenuated line may have a role to play in the expression of this host gene.

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.

Mechanism(s) of attenuation of Theileria annulata vaccine cell lines

Attenuated vaccines are an important means of controlling Theileria annulata infection of cattle. Production is by prolonged cultivation of macroschizont-infected cells. The mechanism of attenuation remains unclear. There are three general nonmutually exclusive possibilities: Selection of avirulent subpopulations, genome rearrangements and alterations in gene expression. Several groups, including ours, have provided evidence that the population structure usually tends to simplify during attenuation. Our data on the T. annulata (Ta) Ankara cell line show that attenuation is not necessarily accompanied by the population becoming clonal. We have been unable to detect large DNA rearrangements. Evidence for alterations in host and parasite gene expression during attenuation is available. With respect to the host we have shown that attenuation is accompanied by loss of expression of parasite induced matrix metalloproteinases (MMPs). However, in different lines different protease activities are involved. In the T. annulata Ode line we have shown that 8 activities (including MMP9) are downregulated and that this correlates with a loss of metastatic behaviour. This has previously been shown in vitro using reconstituted basement membrane (Matrigel) and is demonstrated in vivo using scid mice in this study. Thus part of the pathology, namely the ability to disseminate, mediated by host MMPs, is lost upon attenuation. Re-isolation experiments have shown that the reduction/loss of MMP is a stable transferable trait. A logical extension is that loss of MMP activity (and virulence in general) must be at the most fundamental level a genetic trait of the parasite. Evidence for loss of parasite gene expression is implied by the loss of the ability to differentiate into merozoites on attenuation. Specific evidence for loss of parasite gene expression has been obtained using differential RNA display. We view virulence as a multifactorial phenomenon involving interacting subpopulations of cells and attenuation is a threshold effect whereby the number of virulence factors is reduced below a critical level. On this basis there will be many different ways to achieve attenuation.

Review: Theileria schizonts induce fundamental alterations in their host cells

The sporozoites of Theileria annulata and T. parva invade bovine leukocytes, where they differentiate into schizonts. The latter can immortalize and induce fundamental changes in their host cells. T. annulata infects mainly major histocompatibility complex class II cells, whereas T. parva preferentially transforms T-lymphocytes, which proliferate continuously without the need for exogenously added growth factors. Most of the cell lines appear to be independent of a growth factor but may express several cytokines that influence the outcome of the disease. The mechanisms underlying this transformation are not well understood. The infected cells show increased activity of casein kinase II and Jun NH2-terminal kinase (JNK), whereas extracellular signal-related kinase 1 and 2 and P38 are not activated. In addition, several transcriptional factors such as NFkB and AP-1 are activated. It has been postulated that parasite proteins either expressed on the surface of the schizonts or secreted into the host cell cytoplasm may interfere with the signal-transduction pathway of the host cells. A possible candidate may the casein kinase II homologue that was identified in schizonts of both T. annulata and T. parva.

Infectivity and cross-immunity studies of Theileria lestoquardi and Theileria annulata in sheep and cattle: I. In vivo responses

In a series of experiments, sporozoite stabilates of a Theileria lestoquardi (Lahr) and a T. annulata (Ankara) stock prepared from Hyalomma anatolicum anatolicum ticks, were used to examine the infectivity of both parasite species for sheep and cattle and to study the development of cross-immunity between these parasite species. In the first experiment sheep and cattle were inoculated with T. lestoquardi sporozoites. Surviving animals and naive sheep and cattle were, in the second experiment, inoculated with T. annulata. In the third experiment, naive sheep and sheep previously infected with T. annulata, were inoculated with T. lestoquardi. The following responses to inoculations were monitored: clinical and haematological signs of infection, appearance of parasitic stages of the parasites in lymph node biopsies and in peripheral blood and serological response to T. lestoquardi and T. annulata schizont antigens. While T. lestoquardi readily infected sheep and caused severe disease, it did not infect cattle. On the other hand, T. annulata infected both cattle and sheep. However, whereas cattle became severely affected, infected sheep showed mild clinical symptoms only and piroplasms did not develop. Despite their different behaviour in the host species examined, cross-immunity studies suggested that the parasite species are very closely related. Experiments in sheep indicated that T. lestoquardi infection protected against subsequent T. annulata infection. On the other hand, recovery from T. annulata infection did not prevent infection by sporozoites of T. lestoquardi, resulting in the establishment of schizonts and their subsequent development into piroplasms, although it protected against the major clinical effects of T. lestoquardi infection.

Identification of a Theileria annulata antigen expressed in multiple stages of the parasite life cycle

In order to identify sporozoite surface molecules which may be involved in invasion and could act as potential vaccine candidates, a number of Mabs were raised in mice against T. annulata sporozoites. These were assayed for their ability to block sporozoite invasion of bovine peripheral blood mononuclear (PBM) cells in vitro. One of these, Mab 4B11, was found to neutralize sporozoite invasion to a high degree and to recognize a group of sporozoite antigens on Western blots. A T. annulata lambdagt11 genomic expression library was screened with Mab 4B11 and a positive clone containing a 900-bp insert (KP8) analysed further. Data from Southern and Northern blotting indicated that the gene containing the KP8 sequence, termed sporozoite and macroschizont gene 2 (spm2), was expressed both in T. annulata sporozoites and in later parasite life-cycle stages, macroschizont-infected leucocytes and piroplasms. The KP8 sequence was expressed in E. coli as a fusion protein with glutathione-S-transferase (GST) using the vector pGEX1lambdaT. Bovine antiserum raised against GST-KP8 recognised a single high molecular weight molecule on Western blots corresponding to one of the antigens recognised by Mab 4B11, expressed in sporozoites, macroschizont-infected leucocytes, and piroplasms. While our evidence suggests that the spm2 molecule alone is not responsible for sporozoite neutralization, it is a multistage antigen likely to function both in T. annulata sporozoites and in subsequent parasite life-cycle stages.

Theileria annulata: the expression of two novel macroschizont antigens on the surface of infected mononuclear cells differs during in vitro attenuation of a virulent cell line

The first part of this study of the biological mechanisms underlying attenuation of virulent Theileria annulata macroschizont-infected cell lines screened four pairs of T. annulata (Hisar) in vivo- and in vitro-derived macroschizont-infected cell lines (lines) and identified a single in vivo-derived line, which induced lethal tropical theileriosis. The other seven lines were relatively avirulent. Analysis of the clinical, hematological, and parasitological responses of cattle immunized with different passages of the virulent line after in vitro culture showed that it was partly attenuated by passage (p) 50 and avirulent by p130. Clones representing the three glucose phosphate isomerase (GPI) isotypes, which constituted the newly isolated virulent culture, were obtained from p3 by limiting dilution; p50 and p130 consisted of one isotype. The second part of the study raised monoclonal antibodies (MAbs) against macroschizont-infected cells, as reagents for detecting antigenic differences between virulent and avirulent parasites, and identified two MAbs that recognized the surface of infected cells as well as macroschizonts. MAb EU1 recognized an antigen expressed by all the lines tested, whether in vitro- or in vivo-derived, whether uncloned or cloned, and irrespective of extent of subpassage in culture. MAb EU106 recognized an antigen whose expression by the virulent line and its clones disappeared on passage in culture. This antigen was not expressed at all by the avirulent in vitro-derived line prepared with cells from the same calf. Both antigens were expressed by lines infected with other stocks of T. annulata, including two lines known to induce lethal disease. The different profiles of expression of the two novel antigens, recognized by MAbs EU1 and EU106, by the line undergoing attenuation suggest (1) that the two antigens interact differently with the bovine immune system; and (2) that there are two, very different, potential roles for these antibodies in the development of vaccines against T. annulata infections.

Metastasis of Theileria annulata macroschizont-infected cells in scid mice is mediated by matrix metalloproteinases

Theileria annulata (Ta)-infected leucocytes are able to disseminate in scid mice. The dose of virulent parasites of the Ta-Ode line required to achieve quantifiable dissemination was found to be 2 x 10(6) cells given i.p. Dissemination was higher on day 11 post-inoculation than on day 18. The attenuated Ta-Ode cells were found to disseminate very poorly compared to their virulent progenitors, which correlates with a marked reduction in matrix metalloproteinase (MMP) expression. A daily i.p. injection of mice with BB94, a synthetic inhibitor of MMPs, almost completely ablated dissemination compared to controls. This provides strong evidence that metastasis of Theileria annulata macroschizont-infected host cells is mediated by host MMPs induced by the parasite. This has important implications for explaining a number of pathological features of tropical theileriosis in cattle.

Matrix metalloproteinases mediate the metastatic phenotype of Theileria annulata-transformed cells

Theileria annulata infects and reversibly transforms bovine leucocytes. The parasite-transformed cells are immortalized, metastatic and express a number of metalloproteinases including matrix metalloproteinase 9 which they secrete. All the metalloproteinases observed on substrate gels are inhibited by tissue inhibitor of metalloproteinase 1 and 4 synthetic inhibitors BB94, GM6001, BRL29808AI and Ro31-4724. We have adapted an in vitro assay for metastatic behaviour that measures the ability of parasitized cells to cross reconstituted basement membrane, Matrigel. Using this we demonstrated that macroschizont-infected cells are invasive in vitro and that their invasive properties can be almost eliminated by the same specific inhibitors of metalloproteinases as used in the substrate gels. This demonstrates that the metastatic behaviour of the infected cells is due in part to metalloproteinase activity and strongly suggests a role for the metalloproteinases we observed on gels. This is further supported by the fact that an attenuated vaccine line which shows much reduced metalloproteinase activity also exhibits a marked reduction in metastatic behaviour. We suggest that these metalloproteinases are virulence factors mediating some pathological features of the disease and their loss in the vaccine line could provide an explanation for attenuation.

Theileria annulata: in vitro cultivation of schizont-infected bovine lymphocytes

Experimental parameters of optimization of the in vitro growth conditions for Theileria annulata schizont-infected bovine lymphoid cells are presented. Of the nine different media tested in the course of 14 successive passages, Leibovitz L-15 (L-15) and a combination of McCoy and Leibovitz L-15 (ML) were preferable to McCoy, Dulbecco (DMEM), RPMI 1640 or Eagles's minimum essential medium (MEM) based on either Hank's or Earle's salts. The lowest multiplication rate was obtained with M-199 medium based on Hank's or Earle's salts. The highest yield of cells was obtained when L-15 was supplemented with 20% newborn bovine serum, while lowering the serum concentration by half resulted in a 25% decrease in cell yield. There was no effect on multiplication rate observed during ten passages when 2-mercaptoethanol and a mixture of oxaloacetate, sodium pyruvate and insulin were added to the growth medium. On substitution of conditioned medium for 20 or 50% of the growth medium, the yield of cells decreased by 12 or 20%, respectively, a factor which might be considered in calculations of the cost of anti-T. annulata vaccine production. When cells were grown in stationary cultures in Roux bottles for 7 days without change of medium, the highest yield resulted from seeding at 10(7) cells per vessel (100 ml) in L-15 supplemented with 20% serum. In Roller bottles, with the same type and volume of medium and cultivation for 7 days without medium change, best yield resulted from seeding with the highest inoculum size of 4 x 10(7) cells per vessel.

A preliminary study on the attenuation of Tunisian schizont-infected cell lines of Theileria annulata

Four Theileria annulata cell lines were characterised at low passage levels using two polymorphic markers and then used to infect calves. Their virulence seemed to be related to the number of genotypes present within the cell line. In all, 3 of the 4 cell lines were cultured up to passage 100 or 200 and inoculated into calves. Their characterisation using the same markers indicated that the attenuation was related to a reduction in the parasite polymorphism down to a single genotype. The immunogenicity of the three attenuated cell lines was assessed in calves using two types of challenge. Optimal protection was observed against homologous challenges. The level of immunity to heterologous challenges appeared to decrease with attenuation and seemed to depend on the cell line used.

Theileria annulata: altered gene expression and clonal selection during continuous in vitro culture

Kept in continuous in vitro culture, the protozoan parasite Theileria annulata gradually loses virulence when inoculated into cattle. These attenuated cell lines form the basis of the in vitro live vaccines which have been used successfully to control tropical theileriosis in several endemic regions. In the study reported here, events occurring during in vitro culture of an Indian (Hisar) cell line, which may be associated with the reduction in virulence, have been investigated. Hybridization with two polymorphic DNA probes following Southern blotting showed that selection of particular parasite genotypes occurs very rapidly with culture; a novel hybridization pattern is observed with both probes after 50-100 passages in vitro. In addition to this selection process, immunofluorescence studies using a monoclonal antibody which specifically recognizes virulent T. annulata revealed alterations in antibody reactivity following in vitro culture. This loss of reactivity was observed in three cloned cell lines derived from the early, virulent Hisar line and implies that phenotypic changes resulting from alterations to parasite gene expression are taking place during the attenuation process. When considered with the results from in vivo infections with serial passages of this cell line, it can be proposed that both altered gene expression and selection may be involved in the loss of pathogenicity of T. annulata during continuous in vitro culture.

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.

Infection with Theileria annulata induces expression of matrix metalloproteinase 9 and transcription factor AP-1 in bovine leucocytes

Theileria annulata infects bovine leucocytes and results in their reversible transformation such that they become immortalised and metastatic. The present study describes parasite-induced changes in host cell gene expression which have a direct bearing on this transformation process. T. annulata-infected leucocytes produce a number of novel metalloproteinase activities. One of these, previously called B1, is a 97-kDa protein which is secreted in large amounts and has been purified from protein-free, conditioned medium. An antiserum to this enzyme was used to isolate a cDNA clone. The predicted protein sequence of B1 is 81% identical to human matrix metalloproteinase 9 (MMP9), demonstrating that it is the bovine homologue of this enzyme. RNAase protection assays demonstrated that the MMP9 activity, unique to infected cells, is due to increased MMP9 mRNA levels. We also assayed the levels of transcription factor AP-1 and demonstrated that it was constitutively present in increased amounts in Theileria-infected cells. In addition we assayed the level of mRNA encoding c-Fos, a common component of AP-1 and observed that it was indeed up-regulated in infected cells. Since AP-1 is implicated in the control of the cell cycle, and MMP9 can confer metastatic properties, these results are of considerable significance with respect to the transformed phenotype induced by Theileria infection.

Tropical theileriosis in Bos taurus and Bos taurus cross Bos indicus calves: response to infection with graded doses of sporozoites of Theileria annulata

This work extends basic knowledge of tropical theileriosis in taurine and crossbred cattle. Infection of Bos taurus and Bos taurus cross Bos indicus (Sahiwal) calves with graded doses of sporozoites of Theileria annulata (Hissar), an Indian stock of the parasite, showed the following to be dose dependent in both cattle types: the time to appearance and population size of macroschizonts, microschizonts and piroplasms, time and severity of pyrexia, anaemia manifested by erythrocyte counts and haematocrit. All infections were accompanied by a prompt and severe panleucopenia. This effect was dose related in both the taurine and the Sahiwal crossbred calves. Lymphocyte counts returned to preinfection levels in the blood of animals which recovered, but death from theileriosis was characteristically accompanied by a persistent and severe lymphocytopenia. Flow cytometry using monoclonal antibodies to bovine mononuclear cells was used to identify the lymphocyte subsets involved in lymphocytopenia. The outcome of infection was dose dependent in the crossbred calves but not in taurine calves. Although the results obtained did not differ qualitatively between the two cattle types, they provided some preliminary evidence for resistance to tropical theileriosis in Sahiwal crossbred calves.