Influence of blood group, Glucose-6-phosphate dehydrogenase and Haemoglobin genotype on Falciparum malaria in children in Vihiga highland of Western Kenya

Background

Genetic diversity of ABO blood, glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin type and their ability to protect against malaria vary geographically, ethnically and racially. No study has been carried out in populations resident in malaria regions in western Kenya.

Method

A total of 574 malaria cases (severe malaria anaemia, SMA = 137 and non-SMA = 437) seeking treatment at Vihiga County and Referral Hospital in western Kenya, were enrolled and screened for ABO blood group, G6PD deficiency and haemoglobin genotyped in a hospital-based cross-sectional study.

Result

When compared to blood group O, blood groups A, AB and B were not associated with SMA (P = 0.380, P = 0.183 and P = 0.464, respectively). Further regression analysis revealed that the carriage of the intermediate status of G6PD was associated with risk to SMA (OR = 1.52, 95%CI = 1.029–2.266, P = 0.035). There was, however, no association between AS and SS with severe malaria anaemia. Co-occurrence of both haemoglobin type and G6PD i.e. the AA/intermediate was associated with risk to SMA (OR = 1.536, 95%CI = 1.007–2.343, P = 0.046) while the carriage of the AS/normal G6PD was associated with protection against SMA (OR = 0.337, 95%CI = 0.156–0.915, P = 0.031).

Conclusion

Results demonstrate that blood group genotypes do not have influence on malaria disease outcome in this region. Children in Vihiga with blood group O have some protection against malaria. However, the intermediate status of G6PD is associated with risk of SMA. Further, co-inheritance of sickle cell and G6PD status are important predictors of malaria disease outcome. This implies combinatorial gene function in influencing disease outcome.

Cytoplasmic sequestration of p53 promotes survival in leukocytes transformed by Theileria

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

Improved diagnosis for nine viral diseases considered as notifiable by the world organization for animal health

Nine viral diseases included in the World Organization for Animal Health list of notifiable diseases (former list A) were chosen for their contagiousness and high capacity of spreading to improve their diagnosis using new and emerging technologies. All the selected diseases--foot-and-mouth disease, swine vesicular disease, vesicular stomatitis, classical swine fever, African swine fever, bluetongue, African horse sickness, Newcastle disease and highly pathogenic avian influenza--are considered as transboundary diseases, which detection causes the prohibition of livestock exportation, and, thus, it leads to high economical losses. The applied diagnostic techniques can fall into two categories: (i) nucleic-acid detection, including padlock probes, real-time PCR with TaqMan, minor groove binding probes and fluorescence energy transfer reaction probes, isothermal amplification like the Cleavase/Invader assay or the loop-mediated amplification technology and the development of rapid kits for 'mobile' PCR and (ii) antigen-antibody detection systems like simplified and more sensitive ELISA tests. Besides, internal controls have been improved for nucleic acid-detecting methods by using an RNA plant virus--Cowpea Mosaic Virus--to ensure the stability of the RNA used as a positive control in diagnostic real-time RT-PCR assays. The development of these diagnosis techniques has required the joint efforts of a European consortium in which nine diagnostic laboratories and an SME who have collaborated since 2004 within the European Union-funded Lab-on-site project. The results obtained are shown in this paper.

Development and evaluation of a loop-mediated isothermal amplification method for diagnosis of tropical theileriosis

A loop-mediated isothermal amplification (LAMP) assay was developed and evaluated for diagnosis of tropical theileriosis. A set of six primers was designed based on the unique gene of Theileria annulata (Theileria annulata strain Ankara hypothetical protein (GeneDB TA04795). The protocol for the reaction was setup and the specificity and sensitivity of the assay were established. The specificity experiment showed that LAMP primers amplified T. annulata DNA successfully, while no amplification was seen for Theileria parva, Theileria mutans, Theileria sergenti, Theileria sinensis, Babesia bovis as well as bovine genomic DNA and water control. When the sensitivity of LAMP assay was compared with that of conventional PCR a 10-fold higher sensitivity was found, with a detection limit of 10 pg/microl of genomic DNA isolated from a T. annulata-infected cell line. The LAMP product was confirmed by restriction digestion and staining with SYBR Green I. Furthermore, the LAMP assay was applied for the diagnosis of T. annulata in field samples and compared with reverse line blot (RLB), demonstrating that results of the LAMP assay corresponded to those of RLB. These results indicate that the LAMP assay is rapid and simple to run, cost-effective, sensitive and specific and has potential usefulness for application in epidemiological studies on T. annulata infection of cattle.

Animal health: harmonisation and distribution of pathogen detection and differentiation tools

Quality and safe meat production and livestock husbandry are important foci for addressing the wider underlying economic and political challenges. In the last few years, an intense focus of the scientific community has been placed on breakouts of livestock diseases especially in Asia, which have spread into neighbouring countries including Europe. These outbreaks had a serious impact on the livelihood of the farmers as well as the economy of the affected countries. Given this, the establishment of a network of diagnostic facilities is a great demand both at the national and regional levels. In most of the cases, diagnostic assays are either not available or they are not validated. The aim of this collaborative network was to: 1 Distribute and harmonize diagnostic tools required for pathogen detection and differentiation. 2 Build the capacity to ensure the conduction of integrated disease control measures.

Determination of potential risk factors associated with Theileria annulata and Theileria parva infections of cattle in the Sudan

A multi-variate logistic regression analysis was performed on two sets of data on the prevalence of Theileria annulata in Northern Sudan and Theileria parva in Southern Sudan, to determine the potential risk factors that might affect the distribution of the infections in those regions. The logistic regression model was fit with the tested risk factors for each disease, separately. The results indicated that locations, management systems and age could be held as risk factors for T. annulata infection in Northern Sudan, while for T. parva locations and seasons could be held as risk factors in Southern Sudan. The results of this study will assist in the development of more effective control strategies for smallholder dairy farms in the country.

Epidemiological studies on tick-borne diseases of cattle in Central Equatoria State, Southern Sudan

A herd-based study was carried out in Central Equatoria State, Southern Sudan, to study epidemiological aspects of tick-borne diseases. Six herds of cattle situated in three different locations were selected and investigated every 3 months during the year 2005. Blood smears for Giemsa staining and blood spots on filter paper for deoxyribonucleic acid extraction were collected from 600 apparently healthy indigenous cattle. A total of 69 (11.5%) samples showed the presence of piroplasms in Giemsa-stained blood smears, and polymerase chain reaction increased the detection limit to 297 (49.5%). Using reverse line blot, it was possible to detect and differentiate eight different piroplasms namely, Theileria parva (71.2%), Theileria mutans (73%), Theileria velifera (45.3%), Theileria taurotragi (2.7%), Theileria buffeli (0.5%), Theileria annulata (0.2%), Babesia bovis (1.7%), and Babesia bigemina (0.3%). Mixed infections were detected in 406 samples (67.7%) accounting for 17 different combinations. High infection of Theileria parva was reported among young calves compared to older cattle. The highest prevalence of Theileria parva was reported in the rainy season (October). The implications of these results on the epidemiology of tick-borne diseases are discussed with emphasis on East Coast fever.

At least two genetically distinct large Babesia species infective to sheep and goats in China

A fatal disease of sheep and goats in the northern part of China has been reported to be due to Babesia ovis. However, some characteristics of the causative agent in recent reports are not in accordance with the original attributes ascribed to this parasite. Therefore, the 18S small subunit ribosomal RNA (18S rRNA) genes of a number of Babesia isolates in China were sequenced and compared with that of other Babesia and Theileria species in an attempt to clarify their taxonomic position. In the present study, seven Babesia isolates were collected from distinct areas of northern China, and the 18S rRNA genes were amplified and sequenced. The phylogenetic trees were inferred based on 18S rRNA gene sequences of the Chinese ovine Babesia isolates and some of ovine Babesia and Theileria species available in GenBank. In the phylogenetic tree, Babesia sp. isolates from Madang, Tianzhu, Lintan, Ningxian, Hebei and Liaoning all grouped with B. motasi with 88.2-99.9% identity, while Babesia sp. Xinjiang grouped in a separate clade between B. ovis and B. crassa with 79.7-81.2% identity. The results indicated that there are at least two distinct Babesia species groups-B. motasi and Babesia sp. Xinjiang, the latter was distinctly different from other ovine Babesia isolates from China with less than 86.6% identity.

Serological diagnostic tools for the major tick-borne protozoan diseases of livestock

Tick-borne protozoan diseases, babesiosis and theileriosis, are among the most important diseases affecting the productivity of livestock worldwide and resulting in high economic losses. A prerequisite for the control of these diseases is to study their epidemiology by mapping their distribution and seasonality. As clinical diagnostic and surveillance tools, serological tests such as the complement fixation test (CFT), the indirect fluorescent antibody test (IFAT) and the enzyme linked immunosorbent assay (ELISA) have been successfully used over decades. With the development in molecular biology, recombinantly expressed parasite molecules have emerged and substituted crude parasite antigen used in serology. A popular format of these tests is the antibody binding competitive inhibition and the indirect antibody detection ELISA. Under the precondition that these tests are correctly designed and validated, they provide a powerful tool for epidemiology, with greater advantages of affordability and amenability to standardization. This paper reviews the pathogenic tick-borne protozoan diseases and the respective diagnostic ELISA based serological tests currently available for serosurveillance.

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

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

Development of a recombinant indirect ELISA for the diagnosis of Theileria sp. (China) infection in small ruminants

Theileria sp. (China) causes severe limitations on the development of the livestock industry in the north-west of China. An enzyme-linked immunosorbent assay (ELISA) based on merozoite homogenate of the parasite for diagnosis of infection has been established; however, cross-reactivity with other small ruminant-infecting piroplasms could not be excluded. Thus, a prerequisite for epidemiological surveys and diagnosis was the establishment of a recombinant protein-based ELISA. To this end, serum from Theileria sp. (China)-infected sheep was used to screen a Theileria lestoquardi expression library, resulting in the identification of a specifically reacting clone with a high identity to the heat shock protein 70 (HSP70) of Theileria parva and Theileria annulata and thus named TlHSP70. An HSP70 homologue was also confirmed to be expressed by Theileria sp. (China) merozoites (TcHSP70). A part of the TlHSP70 protein, found to be conserved in TcHSP70, was recombinantly expressed and used to establish an ELISA. A total of 260 field serum samples tested resulted in a sensitivity and specificity of 94.3 and 89.5%, respectively, in comparison with the merozoite homogenate ELISA. The potentials of the application of the test in epidemiological surveys to map out the prevalence of the disease and for routine diagnostics are described.

A new recombinant protein-based ELISA for the diagnosis of malignant theileriosis of sheep and goats

Tick-borne diseases of small ruminants are of highly economic importance in many countries. Malignant theileriosis of sheep and goats caused by Theileria lestoquardi is considered among the most important of these diseases and constitutes an obstacle to the sheep industry in countries like the Sudan. Here the application of a newly discovered surface protein of T. lestoquardi (Clone-5) in an enzyme-linked immunosorbent assay (ELISA) and the potentials of the application of the test in epidemiological surveys and diagnosis are described. Clone-5 contains a predicted number of 20 antigenic determinant sites and two polypeptides derived from the protein were recombinantly produced, purified and tested with control serum samples in both ELISA and Western Blot. One of the polypeptides was further used in validation experiments that involved the testing of negative and positive field serum samples collected from an area that had witnessed an outbreak of malignant theileriosis in Northern Sudan. ELISA, based on this recombinant protein, demonstrated a satisfactory performance with a calculated sensitivity and specificity of 94.6 and 88%, respectively, when countertested with a standard indirect fluorescent antibody test (IFAT). Moreover, no cross-reactions could be demonstrated against Theileria species (China) nor Cowdria spp. This test is recommended for further field validation experiments.

Application of the recombinant Theileria annulata surface protein in an indirect ELISA for the diagnosis of tropical theileriosis

The recombinant surface protein of Theileria annulata (TaSP) was used in the standardization and validation of an enzyme linked immunosorbent assay (ELISA) for the detection of circulating antibodies against tropical theileriosis. ELISA data were expressed as the percentage positivity (PP) of the reactivity of an internal positive control. A total of 50 sera samples from a disease-free area were used for the calculation of the cut-off value which served as a threshold between the positive and the negative sera samples. This was determined as the mean PP plus two standard deviations or the twice the mean PP of the results obtained with these negative samples. The obtained thresholds were 17.8% and 18.3%, respectively. Accordingly, the reactivity of 140 field sera samples collected at random from an area known to be endemic for tropical theileriosis in Sudan was determined as PP values which were then compared to the results obtained using the indirect fluorescence antibody test (IFAT) from the same samples. Both tests showed a high degree of correlation. The TaSP-ELISA had a sensitivity of 99.1% and specificity of 90.47% when taking the IFAT as a reference test. Our test has proved its suitability for the diagnosis of tropical theileriosis and could be used in serological surveys to map out the prevalence of the disease or to monitor vaccination efficiencies in disease-free populations.

Characterization of a polymorphic gene of T. lestoquardi and of a recently identified Theileria species pathogenic for small ruminants in China

In the present study, we identified a gene from Theileria lestoquardi and from a recently described Theileria species which is highly pathogenic for small ruminants in China. Since the taxonomic position of the latter parasite is still not clear, we refer to it as Theileria (China) species. The gene described here comprises an open reading frame of about 948 bp which prospectively encodes a 35-kDa protein. Its sequence is most closely related to the polymorphic immunodominant membrane protein of T. parva (36% identity). A search for sequence patterns and motifs within the predicted amino acid sequence revealed that this gene possesses three membrane-spanning regions at its C-terminal part, suggesting that it is a membrane protein. Several allelic variants of this gene were found in each parasite species, demonstrating interspecies and intraspecies variation. The predicted amino acid sequence variants display a substantial size and sequence polymorphism in the central part of its presumed extracellular region, while the N-terminal and the transmembrane/intracellular regions are highly conserved.

The role of cytokines in immunity and immunopathogenesis of pirolasmoses

Cells involved in innate and adapted immunity produce cytokines capable of orchestrating the immune response to Babesia and Theileria infections. Thus, CD4-postive T cells recognise peptide fragments of the parasites in the context of the major histocompatibility complex (MHC) class II antigen and produce gamma interferon (IFN-gamma) to activate macrophages for enhanced phagocytosis and intracellular killing of the parasites. In addition, CD4-positive T cells produce interleukin 2 (IL-2) which is essential for the clonal expansion of CD8-positive T cells. The latter cells kill Theileria-infected host leucocytes in an MHC class I-dependent manner. On the other hand, the overproduction of proinflammatory cytokines contributes to disease progress.

Phylogenetic analysis by rRNA comparison of the highly pathogenic sheep-infecting parasites Theileria lestoquardi and a Theileria species identified in China

In the Northwestern part of China there have been reports of clinical cases in small ruminants of a haemoparasite with the characteristics of Theileria hirci (T. lestoquardi). However, some properties of this parasites argue against its classification as T. lestoquardi. In this paper, we present evidence that T. lestoquardi and the Chinese Theileria isolate are distinct parasite species. Phylogenetic analysis of determined nucleotide sequences of small subunit ribosomal RNA (srRNA) genes of T. lestoquardi and the Chinese Theileria parasite show that they belong to different clades within the phylogenetic tree of piroplasms. The srRNA sequence of the Chinese parasite was found to be most closely related to T. buffeli, which, with T. sergenti, belongs to an evolutionary lineage of non-lymphoproliferative Theileria species. On the other hand, it was clearly divergent to a lineage of lymphoproliferative Theileria species; T. annulata, T. parva, T. taurotragi, and T. lestoquardi, the latter being most closely related to T. annulata.

Generation of cytotoxic T lymphocytes and cytostatic acting cells in T. annulata-immune cattle

Cattle immunized against Theileria annulata with schizont containing autologous cell lines are immune to challenge with a homologous parasite strain. Two cell types have been detected in the peripheral blood of the immunized animals: cytotoxic T lymphocytes (CTL) and cytostatic acting cells (CAC). Killing the target cells by CTL is infection associated and is MHC class I restricted. Hence, no cytotoxicity was observed against target cells that were treated with the theilericidal drug buparvaquone or autologous Con A-blasts. The growth inhibition of CAC is MHC unrestricted, and not mediated by cytokine interferon gamma (IFN-gamma).

Lymphocyte stimulatory capacity of Theileria annulata-infected ovine lymphoblastoid cells

T. annulata, the causative agent of tropical theileriosis in cattle, is transmitted by ticks of the genus Hyalomma. Sporozoites of this parasite invade their target cells, where they differentiate to macroschizonts. T. annulata additionally invades and transforms ovine and caprine leukocytes. T. annulata infection in the ovine system is poorly studied, thus we used a mixed lymphocyte culture (MLC) to analyze the capacity of these cells to activate naïve uninfected ovine cells. The peak response was observed on day three or four and the response could not be induced by lysates of infected cells or their supernatants. The stimulated cells expressed IL-2 and secreted an IL-2-like growth factor.

Proliferation and cytokine profile of T. annulata-infected ovine, caprine, and bovine lymphoblastoid cells

T. annulata, the causative agent of tropical theileriosis in cattle, can also infect ovine and caprine leukocytes in vitro. In vivo studies showed that this parasite causes a mild infection in both these animal species, and in sheep merozoite stage development seems to be inhibited. Since the nature of T. annulata infected caprine and ovine cells is not known, all three cell lines were karyotyped and phenotypically characterized by flow cytometry. They all express mRNA of cytokines IL-1 alpha, IL-1 beta, IL-8, and TNF-alpha, but not of IFN-gamma, IL-2, and IL-4. In contrast, IL-6 mRNA was expressed in the cattle cell line only, while mRNA of IL-10 was exclusively produced by the sheep cell line. The observed differences in cytokine mRNA expression may be responsible for the different pathogenesis of T. annulata infection in cattle and sheep.

Molecular genetic characterization and subcellular localization of Theileria annulata mitochondrial heat-shock protein 70

A Theileria annulata mitochondrial heat-shock protein of the 70-kDa family (Tamthsp70) was isolated by screening of the cDNA library of a T. annulata-infected bovine lymphoblastoid cell line with an antibody raised against T. annulata schizonts. The Tamthsp70 coding sequence was found to be most closely related to a previously reported mitochondrial hsp70 gene of Eimeria tenella exhibiting a similarity of 67% with mitochondrial hsp70 genes of eukaryotic plants (Pisum sativum, Phaseolus vulgaris) and with dnaK proteins of prokaryotes (Rhizobium meliloti, Agrobacterium tumefaciens). The Tamthsp70 mRNA is expressed within the sporozoite, schizont, and merozoite stages of the parasite, which suggests that it is constitutively transcribed throughout the life cycle. The gene encodes a polypeptide of 681 amino acids and exhibits a mitochondrial targeting sequence and several sequence motifs common to mitochondrial hsp70 and prokaryotic dnaK proteins. The protein level of the Tamthsp70 protein after heat shock decreased slightly during the exposure of infected cells to a temperature of 42 degrees C in comparison with cells cultured at 37 degrees C. By immunofluorescence the protein was located in the area in which the schizonts reside within infected cells. Immunoelectron microscopy showed that the hsp70 protein was predominantly localized in the mitochondria of the parasites. However, it was also found in small amounts in the cytoplasm of the parasite and host cell. This indicates (1) that Tamthsp70 is very probably translated in the parasite cytoplasm and then transported across the mitochondrial membrane into the mitochondrial matrix and (2) that it is transported across the parasite membrane into the host-cell cytoplasm.

Ribosomal small-subunit RNA gene-sequence analysis of Theileria lestoquardi and a Theileria species highly pathogenic for small ruminants in China

A fatal disease of sheep and goats in the northwestern part of China has been reported to be due to Theileria lestoquardi (syn. T. hirci). However, some characteristics of the causative agent are not in accordance with attributes ascribed to this parasite. We therefore determined the nucleotide sequence of the small-subunit ribosomal RNA (srRNA) gene of T. lestoquardi and the parasite identified in China and compared it with that of other Theileria and Babesia species. In the inferred phylogenetic tree the srRNA sequence of the Chinese parasite was found to be most closely related to T. buffeli and clearly divergent from T. lestoquardi, suggesting that it is an as yet unrecognized Theileria species. Extensive structural similarities were observed between the srRNA sequences of T. lestoquardi and T. annulata, revealing a close phylogenetic relationship between these two Theileria species. On the basis of the srRNA nucleotide sequence, polymerase chain reaction (PCR) primers were designed that specifically amplified genomic DNA of the Chinese Theileria species. These primers may be valuable tools in future epidemiology studies.

The proliferation-associated nuclear protein Ki-67 in the bovine system: partial characterisation and its application for determination of the proliferation of Theileria-infected bovine cells

Theileria annulata-infected bovine cells as well as mitogen-stimulated bovine peripheral blood mononuclear cells (PBMC) express a proliferation-associated nuclear protein equivalent to the human Ki-67 protein. In analogy to the human system, the expression of the bovine Ki-67 protein is restricted to proliferating cells only, since (a) Ki-67 expression paralleled [3H]-thymidine incorporation in concanavalin A (Con A)-stimulated bovine PBMC, (b) Ki-67 was not detectable in quiescent bovine cells, and (c) Ki-67 expression in Theileria-infected cells is related to the presence of the parasites within the cytoplasm of the host cells; upon treatment with the theilericidal drug buparvaquone the parasites are destroyed and the cells cease to proliferate and to express the Ki-67 protein. Western-blot analysis of lysates of proliferating bovine cells revealed that the prototype monoclonal antibody Ki-67 and the new equivalent antibody MIB-1 detected one prominent protein band with an apparent molecular weight of 430 kDa. Two cDNA clones (pUC18.B1.Ki-67 and pUC18.B2.Ki-67) were isolated from a lambdagt11 cDNA library of T. annulata-infected bovine cells by immunoscreening with the monoclonal antibody MIB-1. Comparison of these cDNA sequences with those of the human Ki-67 protein revealed 60-70% identity. Within the "Ki-67 motif", identity proved to be 80% at the amino acid level. The remarkable identity between bovine and human Ki-67 proteins suggests that MIB-1 can be used as a marker for cell proliferation in animal research. In this context we could identify proliferating cells in lymph nodes of Theileria-infected animals and, furthermore, we could distinguish between infected and uninfected proliferating cells using MIB-1 and an antiserum against a recombinant parasite protein designated SA288.

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.

Review: the cellular basis of the immunity to and immunopathogenesis of tropical theileriosis

The intracellular protozoan parasite Theileria annulata causes a severe and often fatal disease of pure and crossbred cattle in tropical and subtropical countries. Animals that recover from the infection are immune against challenge with homologous parasite strains. In the present review we refer to the role of immunocompetent cells and their products in containing the infection or in facilitating the progress of the disease. Parasite-infected host cells produce cytokines, which, depending on their concentration and timing of production, may enhance the establishment of the infection. Thus, cell lines producing high levels of proinflammatory cytokines cause severe postvaccinal reactions when inoculated into cattle. This may be supported by an aberrant non-specific activation of naive T-cells, leading to the production of high levels of gamma-interferon (IFN-y). Under these circumstances development of the specific immune response may be inhibited. At this stage, innate immune reactions are operating to contain the infection. Natural killer cells and macrophages may represent the most important part of this immunity. Antibodies and specific T-lymphocytes, CD4+ T-cells and cytotoxic T-lymphocytes (CTLs), play the most important role in a challenge infection. In this context, CD4+ T-cells produce cytokines required for the clonal expansion of CTLs that kill their target cells in a major histocompatibility complex (MHC) class I-restricted manner. In addition, CD4+ T-cells produce macrophage-activating cytokines such as IFN-gamma. Such activated macrophages produce mediators such as NO, which destroy the intracellular schizonts. Attempts have been directed toward the identification of parasite antigens involved in the induction of immunity. To date, only a limited number of sporozoite and merozoite antigens have been identified and examined for their immunogenicity, and the protection achieved is partial. An effective vaccine must include schizont proteins, notably, those proteins that are secreted into the host cell cytoplasm because these may have access to the MHC class I and II compartments to be presented to CTLs and CD4+ T-cells, respectively. Several schizont proteins have been identified and these are now under investigation.

Innate and adaptive immune responses co-operate to protect cattle against Theileria annulata

For many years it was assumed that Theileria annulata resembled T. parva, parasitizing lymphocytes and causing lymphoproliferative disease, with the two species being controlled by similar protective immune responses. Patricia Preston et al. here review the evidence that has led to a different view of T. annulata. It is now thought that the schizonts of T. annulata inhabit macrophages and B cells, and that tropical theileriosis is not a lymphoproliferative disease. Both innate and adaptive responses contribute to recovery from infection and resistance to challenge and cytokines produced by infected and uninfected cells influence the outcome of infection. Partial protection has been stimulated recently by defined recombinant antigens; efficacy depended upon the delivery system.

Is interleukin 2 necessary for the autocrine proliferation of Theileria-infected bovine cells?

Theileria-infected bovine lymphoblastoid cells are induced to proliferate permanently such that the division of the parasites and that of their host cells occur synchronously. The mechanism by which the parasites induce the transformation of their host cells is unknown. We investigated the growth-factor dependency of a number of Theileria-infected cell lines. Supernatants of the majority of the cell lines tested in our study showed no growth-enhancing activity. However, supernatants of a limited number of cell lines occasionally enhanced the growth of parasitized cells that were used as responder cells. Thus, they contained a growth factor whose biological effect was not eliminated by an anti-interleukin-2 (anti-IL-2) antibody. Moreover, neither the proliferation of T. parva-infected cells nor that of T. annulata-infected cells was impaired by this antibody. In contrast, the anti-IL-2 antibody substantially prevented bovine peripheral blood mononuclear cells from undergoing a proliferative response upon stimulation with concanavalin A (Con A). In line with these results we observed that unlike Con A-stimulated lymphocytes, the infected cell lines did not express IL-2 mRNA. Taken together, our results suggest that Theileria-infected cells do not secrete IL-2 and that IL-2 does not play an important role in the autocrine proliferation of the parasitized host cells.

Evidence for strain specificity in cytotoxic T-lymphocyte-mediated, major histocompatibility complex class I-dependent killing of Theileria annulata-infected cells

Cattle immunised against Theileria annulata with one parasite strain have been found to be immune to re-challenge with different strains of the parasite. However, recent evidence of apparent strain specificity has been documented in cattle immunised with attenuated parasite-infected cells. In this study the strain specificity of major histocompatibility complex class I-restricted cytotoxic T-lymphocytes (CTL), a major anti-parasite effector mechanism, was examined. CTL generated following challenge with the Hissar (Indian) strain effectively lysed autologous cells infected with this strain of the parasite. However, CTL were less effective against cells infected with the Gharb (Moroccan) strain and showed virtually no reactivity against the Ankara (Turkish) strain, providing the first direct evidence for strain specificity in immune responses against T. annulata.

Detection and differentiation of Theileria annulata and Theileria parva using macroschizont-derived DNA probes

A lamda gt11 expression library based on T.annulata-infected cells was screened with an antiserum raised in rabbits against partially purified schizonts of T.annulata. Two clones were detected, sequenced and designated as SA288 and SB288 (Shayan et al., submitted for publication). From the sequences of these two genes oligonucleotide primers were designed for specific amplification of parasite DNA by polymerase chain reaction (PCR). We could show that these genes are of parasitic origin and do occur in all T.annulata stocks tested in the present study. In addition, a target sequence for SA288 could also be identified in T.parva-schizonts. None of them reacted with genomic DNA of different Babesia spp. A third primer pair was designed from the DNA-sequence of a gene encoding for the T.parva-specific casein kinase II-alpha subunit. Using this primer pair, a target sequence could only be detected in T.parva. Taken together, the primers described here can be used as molecular tools in PCR for the detection of Theileria parasites and to distinguish T.annulata from T.parva.

Macroschizonts of Theileria annulata as vaccine and diagnostic tools

T. annulata-infected cells present infection-associated peptides. These peptides represent target molecules of the cytotoxic acting cells. Their preparation and characterization may help to develop a sub-unit vaccine. Our studies show that macroschizont-infected bovine cells can be used as parasite antigen in serology for the detection of parasite-specific antibodies in serum of infected animals. Primers derived from the macroschizont of T. annulata can be used as molecular tools for the detection of parasite DNA in blood samples of carrier cattle.

Theileria-mediated constitutive expression of the casein kinase II-alpha subunit in bovine lymphoblastoid cells

Theileria-infected cells are induced to undergo a transformation that is reversible, since their proliferation is inhibited after elimination of the schizonts by the theilericidal drug buparvaquone. The molecular mechanisms of the transformation remain unknown. The experiments described in the present report deal with the role of casein kinase (CK) II, a serine/threonine protein kinase, in the permanent proliferation of the parasitized cells and show that the CK II-alpha subunit is expressed in both T. annulata- and T. parva-infected cells and that its expression is closely related to the presence of the parasites in the host-cell cytoplasm. Thus, elimination of the schizonts by buparvaquone leads to the inhibition of CK II-alpha subunit mRNA expression without affecting the expression of actin. Cells treated with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) are inhibited in a dose-dependent manner from under-going DNA synthesis as measured by [3H]-thymidine incorporation and from expressing CK II. Furthermore, a host-cell-specific CK II-alpha antisense inhibits DNA synthesis in a dose-dependent manner. In the present study, 6 microM antisense reduced [3H]-thymidine incorporation by Theileria-infected bovine cells to about 50%. Using a primer derived from T. parva CK II, we detected a parasite-specific CK II mRNA in T. parva-infected cell lines. Interestingly. DRB also inhibited the expression of the parasite-specific CK II. However, to date we have not detected a target sequence for this primer in T. annulata schizonts.

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.

Effect of buparvaquone on the expression of interleukin 2 receptors in Theileria annulata-infected cells

Theileria annulata-infected cells were cultured in the presence or absence of human recombinant interleukin 2 (hrIL-2). This growth factor proved to be capable of enhancing the growth of the infected cells: its effect was marked, particularly when the cells were seeded at low densities, and it varied from cell line to cell line. The infected cells produced a factor that possessed the biological activities of IL-2, since their supernatants could enhance the proliferation of concanvalin A-stimulated (Con A) blasts. The reactivity of the parasitized cells to hrIL-2 was abolished following their treatment with the antitheilerial drug buparvaquone. In addition, the drug inhibited the binding of 125I-IL-2 to T. annulata-infected cells but failed to suppress its binding to Con A blasts. Northern blot analysis revealed that the drug had no effect on the expression of the alpha chain of the IL-2 receptor (IL-2R). Therefore, it is possible that buparvaquone interferes with the expression of the beta chain of the IL-2R. The role of IL-2 and the IL2R in the permanent proliferation of T. annulata-infected cells is discussed.

Effect of cyclosporin A on the proliferation of bovine lymphocytes to concanavalin A and on the growth of Theileria annulata-infected bovine cells

After being inoculated by Hyalomma ticks, the sporozoites of Theileria annulata invade bovine lymphocytes, where they subsequently differentiate to schizonts. The infected cells are induced to a continuous proliferation which can be enhanced by human recombinant interleukin 2 (hrIL-2). In the present study, we examined the influence of cyclosporin A (CsA) on the growth of schizont-containing cells and compared with its effect on bovine peripheral blood lymphocytes (PBL) responding to Concanavalin A (ConA). In both cell types, the proliferation was inhibited in a dose dependent manner, which was not restorable in T. annulata-infected cells even after addition of hrIL-2. In contrast, ConA-blasts were able to undergo a proliferative response provided they were treated with high doses of CsA. Both, T. annulata-infected cells and bovine ConA-blasts express IL-2 receptors (IL-2R). The binding of radiolabelled hrIL-2 to ConA-blasts and T. annulata-infected cells was only partially inhibited after treatment with CsA. CsA was not toxic for the parasites, since the treated cells still contained schizonts which did not show any morphological abnormality.

Application of luminol-dependent chemiluminescence to assay opsonizing antibodies to procyclic forms of Trypanosoma congolense in the sera of dogs experimentally infected with heterologous stocks

Luminol-dependent chemiluminescence (LCL) responses of dog granulocytes were used to assay opsonizing antibodies to procyclic culture forms of T. congolense. A high degree of sensitivity was demonstrated and LCL levels were high, when the phagocytic cells were incubated with the sera of infected dogs even at dilutions as high as 1:400 as compared to pre-infection or negative sera. The levels of opsonizing antibodies were elevated in all the dogs throughout the time of observation. The technique was sensitive, could be automated and, therefore, allows a rapid evaluation of large numbers of serum samples for Trypanosoma specific antibodies.

Buparvaquone but not cyclosporin A prevents Theileria annulata-infected bovine lymphoblastoid cells from stimulating uninfected lymphocytes

The influence of Buparvaquone on the morphology, proliferation, and stimulation with T and B cell mitogens of Theileria annulata-infected cells was studied. In addition, the stimulatory capacity of the infected cells before and after treatment with Buparvaquone or cyclosporin A (CsA) was also examined and compared to that of ConA-stimulated bovine peripheral blood cells (PBL). After incubation of the cells for 4 days with Buparvaquone only few schizonts were detectable in the cells. Prolongation of the incubation time to 8, 12, or 14 days eliminated completely the parasites. Despite the elimination of the parasites, the cells were still unable to undergo a proliferative response to Con A or PWM. However, the drug did not interfere with the response of normal PBL to these mitogens. Furthermore, Buparvaquone but not CsA inhibits the generation of mixed lymphocyte reaction (MLR). None of the drugs could prevent ConA-blasts from stimulating autologous PBL. These results suggest that the antigen expressed by the infected cells and recognised by the responder PBL was induced by the schizonts.

In vitro proliferative and cytotoxic responses of PBL from Theileria annulata-immune cattle

Peripheral blood lymphocytes were isolated from healthy calves and were subsequently infected with sporozoites of Theileria annulata in vitro. The infected cells were passaged for 50 times and thereafter inoculated into animals from which they were previously isolated. Within 4-5 days, schizont-containing cells were demonstrable in the lymph nodes of all animals. Few days later, merozoites were detected in erythrocytes. A slight decrease in the counts of lymphocytes and leucocytes was also found. After 2 months these animals and a group of uninfected calves were heavily infected by tick-infestation and showed severe symptoms of theileriosis with 60% schizont-containing cells in the lymph nodes and a parasitaemia of about 35%. Because of the severity of the infection, all control calves were treated with Halofuginone. In contrast, the initially immunized cattle (by inoculation of culture cells), survived the infection without chemotherapy. Less than 10% of their lymph node cells contained schizonts, whereas less than 1% of their erythrocytes were found to be infected with merozoites. In all immunized animals, specific cytotoxic PBL, with the capacity to lyse autologous but not allogeneic infected cells, were demonstrated. In addition, a population of PBL were found to be able to inhibit the growth of T.annulata-infected culture cells in vitro. However, in comparison to PBL of immune animals, PBL of acute infected calves were superior in their capacity to inhibit the proliferation of schizont-containing cells. In mixed lymphocyte reactions, T. annulata-infected cells could induce a more pronounced proliferative response in PBL from immune than in PBL of uninfected animals.

The intermediate-affinity interleukin (IL)2 receptor expressed on Theileria annulata-infected cells comprises a single IL 2-binding protein. Partial characterization of bovine IL2 receptors

Bovine high-, intermediate- and low-affinity interleukin 2 receptors (IL2R) were studied by ligand binding and affinity labeling using 125I-labeled IL2 and homobifunctional chemical cross-linking reagents. High- (Kd = 17 pM) and low-affinity (Kd greater than 6 nM) IL 2R were detected on concanavalin A-activated peripheral blood lymphocytes (PBL). Theileria annulata (TA)-infected autonomously growing PBL (TA-PBL) express predominantly intermediate-affinity IL2R (Kd = 1 nM). Affinity-labeling studies revealed that the high-affinity IL2R comprises a 55-kDa (L chain) and an additional 90-kDa IL 2-binding protein (H chain). TA-PBL express predominantly the H chain. In contrast to the human chain, the bovine form was not separable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/urea into the two distinct bands H1 and H2 and ran in parallel to the human H2 band. These results suggest (a) that the bovine intermediate-affinity IL2R comprises a single H chain and (b) that the single H chain and the L chain are sufficient to form the functional high-affinity bovine IL2R.

Enhancement of neutrophil adherence to Toxocara canis larvae by the C3 component of complement and IgG antibodies

In the present study, the binding human neutrophils to Toxocara canis larvae was examined in vitro. It was found that IgG and/or the C3 component of complement were able to enhance the attachment of the cells to the parasites. This was associated with the generation of strong chemiluminescence reactions. Despite the binding of the cells, the larvae were able to escape and to maintain their infectivity. This was apparent, since the parasites could survive and migrate into different organs including the brain after having been inoculated into mice.

The role of antibodies in immunity against Theileria annulata infection in cattle

The role of antibodies in protecting cattle against Theileria annulata infection was investigated. It was found that serum samples from immune cattle had a neutralizing effect on the sporozoites preventing in this way the invasion of lymphocytes. However, the same antiserum neither caused lysis of macroschizont- infected lymphoblastoid cells nor inhibited their proliferation in vitro. Free merozoites but not the infected erythrocytes were opsonized by immune serum. In addition, complement alone, without antibody participation, was able to lyse free merozoites. The importance of humoral factors in immunity to T. annulata infection is discussed.

The role of interleukin 2 (IL 2) in the proliferation of Theileria annulata-infected bovine lymphocytes

The role of interleukin 2 (IL 2) in the proliferation of Theileria annulata-infected lymphoblastoid cells was studied. It was found that these cells neither require nor produce IL 2. This was based on the following findings: (a) The growth of T. annulata-infected cells was not enhanced by addition of IL 2 to the culture medium. (b) IL 2-dependent Con A-stimulated bovine peripheral blood lymphocytes (Con A-blasts) no longer required IL 2 after being infected with sporozoites of T. annulata. (c) The supernatants of T. annulata-infected cells did not support growth of IL 2-dependent Con A-blasts.

Application of chemi- and bioluminescence in studies of immunological reactions against protozoa

The opsonization and lysis of different protozoa by antibodies and/or complement was followed using luminol-dependent chemiluminescence and bioluminescence. The addition of immune serum to variable antigen type populations of Trypanosoma evansi led to the specific opsonization of trypanosomes resulting in an intense metabolic activation and chemiluminescence response of phagocytic cells. In comparison to those of uninfected control mice, the phagocytosis of coccidia merozoites by spleen cells from mice infected with Eimeria falciformis was enhanced during the acute stage of a primary infection. Opsonizing activity was demonstrated in phosphate-buffered saline extracts of gut contents of mice infected for 10 days. The incubation of E. falciformis merozoites together with guinea-pig complement resulted in slow lysis of the cells. The addition of mouse serum collected greater than 6 days after an infection led to an accelerated lysis of the merozoites, indicating the appearance of complement-fixing antibodies in the serum. Heat-inactivated immune serum alone had no lysing activity on merozoites. In the presence of complement, bovine lymphoblastoid cells infected with Theileria annulata were lysed by anti-lymphoblastoid cell serum raised in mice but not by serum from cattle which had developed immunity to Theileria annulata.

Variant specific opsonization of Trypanosoma evansi measured by luminol-dependent chemiluminescence

Using luminol-dependent chemiluminescence (LCL), the specificity of antibodies to variable antigen type (VAT)-populations of Trypanosoma evansi was studied in four infected ponies. Trypanosomes of each wave of parasitemia were isolated and multiplied in irradiated mice. Their opsonization by serum collected during the infection was investigated with LCL and results for isolated VAT-populations are shown in the paper. Antibodies specific to each VAT-population were first found three days after the maximum of a parasitemic wave. There was no cross reactivity between different VAT-populations. LCL proved to be a rapid and automatic method for the demonstration of antibodies with specificity to variable antigen types of trypanosomes.

Antigenic variation of Trypanosoma evansi in rabbits

In order to study the occurrence and sequential appearance of antigenic variation during the course of T. evansi-infection, rabbits were infected with a clone prepared from T. evansi, Java/55/PTV/1 (stock 1, clone 5). During the course of infection, trypanosome-populations were isolated from the cerebrospinal fluid and from each parasitaemia peak. Specific antisera against the clone, 6 parasitaemia-populations and two different liquor-populations (all isolated from 1 rabbit), were produced in rabbits. These antisera were used for the characterization and comparison of trypanosome populations with each other by means of immunolysis as well as neutralisation-infectivity-(NIF)-test. It was found that in all infected rabbits, the first parasitaemia contained trypanosomes, which were almost identical to those present in the clone. However, the clone contained already minor variant antigenic types ("minor-VATs"). All trypanosome-populations isolated from rabbits were heterogeneous. Heterogeneity was more pronounced in the later phases of the infection. After each fluctuating parasitaemia new dominant variants ("major VAT") were expressed. The sequential appearance of antigenic variation was similar among all infected animals. The effectivity of immunolysis was checked by the NIF-test. As it was expected, complete lysis of all trypanosomes of a population was not achieved, because some "minor VATs" could escape the influence of the antiserum. By this way, they formed the basis of new "major VATs" which dominated in the next fluctuating parasitaemia.

Immediate type hypersensitivity in murine coccidiosis

Subcutaneous injection of soluble merozoite antigen into the footpad of mice previously infected with Eimeria falciformis caused an immediate type hypersensitivity as measured by footpad swelling (FPS). This reaction was first demonstrable ten days after the infection. Maximal values were achieved on day 13, and later on the intensity of FPS decreased. Increase in the dose of oocysts or in the number of infections did not enhance the degree of FPS. The reaction was transferable to normal recipients with immune serum.