Characterization of an insect cell-derived Theileria parva sporozoite vaccine antigen and immunogenicity in cattle

Development of a dual vaccine against East Coast fever and lumpy skin disease

East Coast fever is an acute bovine disease caused by the apicomplexan parasite Theileria parva and is regarded as one of the most important tick-vectored diseases in Africa. The current vaccination procedure has many drawbacks, as it involves the use of live T. parva sporozoites. As a novel vaccination strategy, we have constructed the recombinant lumpy skin disease virus (LSDV) named LSDV-SODis-p67HA-BLV-Gag, encoding a modified form of the T. parva p67 surface antigen (p67HA), as well as the bovine leukemia virus (BLV) gag gene for the formation of virus-like particles (VLPs) to potentially enhance p67 immunogenicity. In place of the native sequence, the chimeric p67HA antigen has the human tissue plasminogen activator signal sequence and the influenza hemagglutinin A2 transmembrane domain and cytoplasmic tail. p67HA was detected on the surface of infected cells, and VLPs comprising BLV Gag and p67HA were produced. We also show that higher multiple bands observed in western blot analysis are due to glycosylation of p67. The two vaccines, pMExT-p67HA (DNA) and LSDV-SODis-p67HA-BLV-Gag, were tested for immunogenicity in mice. p67-binding antibodies were produced by vaccinated animals, with higher titers detected in mice vaccinated with the recombinant LSDV. This candidate dual vaccine warrants further testing in cattle.

Characterization of a Novel Chimeric Theileria parva p67 Antigen Which Incorporates into Virus-like Particles and Is Highly Immunogenic in Mice

The current method to protect cattle against East Coast Fever (ECF) involves the use of live Theileria parva sporozoites. Although this provides immunity, using live parasites has many disadvantages, such as contributing to the spread of ECF. Subunit vaccines based on the sporozoite surface protein p67 have been investigated as a replacement for the current method. In this study, two DNA vaccines expressing recombinant forms of p67 designed to display on retrovirus-like particles were constructed with the aim of improving immunogenicity. The native leader sequence was replaced with the human tissue plasminogen activator leader in both vaccines. The full-length p67 gene was included in the first DNA vaccine (p67); in the second, the transmembrane domain and cytoplasmic tail were replaced with those of an influenza A virus hemagglutinin 5 (p67HA). Immunofluorescent staining of fixed and live transfected mammalian cells showed that both p67 and p67HA were successfully expressed, and p67HA localised on the cell surface. Furthermore, p67HA was displayed on the surface of both bovine leukaemia virus (BLV) Gag and HIV-1 Gag virus-like particles (VLPs) made in the same cells. Mice vaccinated with DNA vaccines expressing p67 and p67HA alone, or p67HA with BLV or HIV-1 Gag, developed high titres of p67 and BLV Gag-binding antibodies. Here we show that it is possible to integrate a form of p67 containing all known antigenic domains into VLPs. This p67HA–VLP combination has the potential to be incorporated into a vaccine against ECF, as a DNA vaccine or as other vaccine platforms.

Molecular and Antigenic Properties of Mammalian Cell-Expressed Theileria parva Antigen Tp9

East Coast Fever (ECF), caused by the tick-borne apicomplexan parasite Theileria parva, is a leading cause of morbidity and mortality in cattle of sub-Saharan Africa. The infection and treatment method (ITM) is currently the only vaccine available to control T. parva. Although ITM elicits levels of protection, its widespread adoption is limited by costs, laborious production process, and antibiotic co-treatment requirement, necessitating the development of a more sustainable vaccine. To this end, efforts have been concentrated in the identification of new T. parva vaccine antigens and in the development of suitable platforms for antigen expression. In this study, we investigated the molecular and antigenic properties of T. parva antigen Tp9 expressed by mammalian cells. Data indicate that Tp9 contains a signal peptide that is weakly functional in mammalian cells. Thus, Tp9 secretion from mammalian cells increased 10-fold after the native signal peptide was replaced with the human tissue plasminogen activator signal peptide (tPA). Sera from all T. parva-immune cattle recognized this recombinant, secreted Tp9. Additionally, PBMC from ITM-immunized cattle produced significant (p < 0.05) amounts of IFNγ following ex vivo exposure to Tp9, but this response varied between cattle of different MHC class I and class II genotypes. In addition, depletion experiments demonstrated that IFNγ to Tp9 was primarily produced by CD4⁺ T cells. Molecular analysis demonstrated that Tp9 presents a signal peptide that is weakly functional in mammalian cells, suggesting that it remains within lymphocytes during infection. Tp9 secretion from mammalian cells was substantially increased when the tPA secretion signal sequence was substituted for the native secretion signal sequence. Using full-length, recombinant Tp9 secreted from mammalian cells, we demonstrated that T. parva-immune cattle develop both humoral and cellular immune responses to this antigen. Collectively, these results provide rationale for further evaluation of Tp9 as a component of a T. parva subunit vaccine.

Immune parameters to p67C antigen adjuvanted with ISA206VG correlate with protection against East Coast fever

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Three doses of p67C antigen generated stronger immune responses than two doses.

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Antibody titers and CD4⁺ T-cell proliferation correlated with protection against ECF.

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The number of doses could not be reduced from three to two without compromising the protection.

East Coast fever (ECF) is a lymphoproliferative disease caused by the tick-transmitted protozoan parasite Theileria parva. ECF is one of the most serious cattle tick-borne diseases in Sub-Saharan Africa. We have previously demonstrated that three doses of the C-terminal part of the sporozoite protein p67 (p67C) adjuvanted with ISA206VG confers partial protection against ECF at a herd level. We have tested the efficacy of two doses of this experimental vaccine, as reducing the vaccination regimen would facilitate its deployment in the field. We reconfirm that three antigen doses gave a significant level of protection to severe disease (46%, ECF score < 6) when compared with the control group, while two doses did not (23%). Animals receiving three doses of p67C developed higher antibody titers and CD4⁺ T-cell proliferation indices, than those which received two doses. A new panel of immune parameters were tested in order to identify factors correlating with protection: CD4⁺ proliferation index, total IgG, IgG1, IgG2 and IgM half maximal titers and neutralization capacity of the sera with and without complement. We show that some of the cellular and humoral immune responses provide preliminary correlates of protection.

Assessment and optimization of Theileria parva sporozoite full-length p67 antigen expression in mammalian cells

Delivery of various forms of recombinant Theileria parva sporozoite antigen (p67) has been shown to elicit antibody responses in cattle capable of providing protection against East Coast fever, the clinical disease caused by T. parva. Previous formulations of full-length and shorter recombinant versions of p67 derived from bacteria, insect, and mammalian cell systems are expressed in non-native and highly unstable forms. The stable expression of full-length recombinant p67 in mammalian cells has never been described and has remained especially elusive. In this study, p67 was expressed in human-derived cells as a full-length, membrane-linked protein and as a secreted form by omission of the putative transmembrane domain. The recombinant protein expressed in this system yielded primarily two products based on Western immunoblot analysis, including one at the expected size of 67 kDa, and one with a higher than expected molecular weight. Through treatment with PNGase F, our data indicate that the larger product of this mammalian cell-expressed recombinant p67 cannot be attributed to glycosylation. By increasing the denaturing conditions, we determined that the larger sized mammalian cell-expressed recombinant p67 product is likely a dimeric aggregate of the protein. Both forms of this recombinant p67 reacted with a monoclonal antibody to the p67 molecule, which reacts with the native sporozoite. Additionally, through this work we developed multiple mammalian cell lines, including both human and bovine-derived cell lines, transduced by a lentiviral vector, that are constitutively able to express a stable, secreted form of p67 for use in immunization, diagnostics, or in vitro assays. The recombinant p67 developed in this system is immunogenic in goats and cattle based on ELISA and flow cytometric analysis. The development of a mammalian cell system that expresses full-length p67 in a stable form as described here is expected to optimize p67-based immunization.

East Coast fever, caused by the tick-borne protozoan parasite Theileria parva, is a disease that results in significant bovine morbidity, mortality, and production losses in regions of sub-Saharan Africa. Susceptible cattle develop clinical signs within a 7–14 days of exposure, which often progress to severe pulmonary edema and death. Control of East Coast fever in affected regions of Africa is largely prohibited by the lack of an affordable and efficacious vaccine. Furthermore, pastoralist farmers in affected regions of Africa often lack resources to prevent losses due to East Coast fever, so these production losses play a significant role in food security and protein availability. Experimental immunization of cattle with a recombinant T. parva-derived antigen, p67, has shown promise in preventing East Coast fever, but this antigen is extremely difficult to produce in full-length in sufficient quantities, and results of immunization studies using truncated recombinant p67 products are highly inconsistent. In this study, p67 antigen production was optimized and produced for use in future immunization studies. Optimization of p67-based immunization strategies is an important step forward in the development of a sustainable, next-generation vaccine against T. parva, which is urgently needed to minimize losses associated with East Coast fever.

Current status of vaccine development against Theileria parasites

The tick-borne protozoan parasites Theileria parva and Theileria annulata cause economically important diseases of cattle in tropical and sub-tropical regions. Because of shortcomings in disease control measures based on therapy and tick control, there is a demand for effective vaccines against these diseases. Vaccines using live parasites have been available for over two decades, but despite their undoubted efficacy they have not been used on a large scale. Lack of infrastructure for vaccine production and distribution, as well as concerns about the introduction of vaccine parasite strains into local tick populations have curtailed the use of these vaccines. More recently, research has focused on the development of subunit vaccines. Studies of immune responses to different stages of the parasites have yielded immunological probes that have been used to identify candidate vaccine antigens. Immunisation of cattle with antigens expressed in the sporozoite, schizont or merozoite stages has resulted in varying degrees of protection against challenge. Although the levels of protection achieved have not been sufficient to allow exploitation for vaccination, there are clearly further lines of investigation, relating to both the choice of antigens and the antigen delivery systems employed, that need to be pursued to fully explore the potential of the candidate vaccines. Improved knowledge of the molecular biology and immunology of the parasites gained during the course of these studies has also opened up opportunities to refine and improve the quality of live vaccines.

Theileria: intracellular protozoan parasites of wild and domestic ruminants transmitted by ixodid ticks

Theileria are economically important, intra-cellular protozoa, transmitted by ixodid ticks, which infect wild and domestic ruminants. In the mammalian host, parasites infect leukocytes and erythrocytes. In the arthropod vector they develop in gut epithelial cells and salivary glands. All four intra-cellular stages of Theileria survive free in the cytoplasm. The schizont stages of certain Theileria species induce a unique, cancer-like, phenotype in infected host leukocytes. Theileria undergoes an obligate sexual cycle, involving fusion of gametes in the tick gut, to produce a transiently diploid zygote. The existence of sexual recombination in T. parva has been confirmed in the laboratory, and is presumed to contribute to the extensive polymorphism observed in field isolates. Key parameters in T. parva population dynamics are the relative importance of asymptomatic carrier cattle and animals undergoing severe disease, in transmission of the parasite to ticks, and the extent of transmission by nymphs as compared to adult ticks. Tick populations differ in vector competence for specific T. parva stocks. Recombinant forms of T. parva and T. annulata sporozoite surface antigens induce protection against parasite challenge in cattle. In future, vaccines might be improved by inclusion of tick peptides in multivalent vaccines.

Vaccines for viral and parasitic diseases produced with baculovirus vectors

The baculovirus-insect cell expression system is an approved system for the production of viral antigens with vaccine potential for humans and animals and has been used for production of subunit vaccines against parasitic diseases as well. Many candidate subunit vaccines have been expressed in this system and immunization commonly led to protective immunity against pathogen challenge. The first vaccines produced in insect cells for animal use are now on the market. This chapter deals with the tailoring of the baculovirus-insect cell expression system for vaccine production in terms of expression levels, integrity and immunogenicity of recombinant proteins, and baculovirus genome stability. Various expression strategies are discussed including chimeric, virus-like particles, baculovirus display of foreign antigens on budded virions or in occlusion bodies, and specialized baculovirus vectors with mammalian promoters that express the antigen in the immunized individual. A historical overview shows the wide variety of viral (glyco)proteins that have successfully been expressed in this system for vaccine purposes. The potential of this expression system for antiparasite vaccines is illustrated. The combination of subunit vaccines and marker tests, both based on antigens expressed in insect cells, provides a powerful tool to combat disease and to monitor infectious agents.

Novel baculovirus-derived p67 subunit vaccines efficacious against East Coast fever in cattle

Two novel baculovirus-derived recombinant Theileria parva p67 constructs were tested for their vaccine potential against East Coast fever. Boran calves were immunized with a his-GFP-p67 fusion protein (GFP:p67deltaSS) or with GP64:p67C, a protein fusion between a C-terminal domain of p67 and the baculovirus envelope protein GP64. Both GFP:p67deltaSS and GP64:p67C induced antibodies with high ELISA titers that neutralized T. parva sporozoites with high efficiency. Upon challenge, a correlation was observed between the in vitro neutralizing capacity and the reduction in severe ECF for individual animals. A protection level upto 85% was obtained. This level of protection was achieved with only two inoculations of 100 microg per dose, which is a major improvement over previous recombinant p67 products.

Development of a chitinase and v-cathepsin negative bacmid for improved integrity of secreted recombinant proteins

The application of the baculovirus-insect cell expression system for the production of integral membrane and secreted proteins is often more troublesome than for cytoplasmic proteins. One protein expressed at low levels in insect cells is the Theileria parva sporozoite surface protein p67. Theileria parva is a protozoan parasite, which causes the tick-transmitted disease East Coast fever in cattle. Baculovirus vectors were engineered to produce a secreted form of p67 by replacing the signal peptide of p67 with the honeybee mellitin signal sequence and deleting a putative membrane anchor from the C-terminus. Furthermore, the chitinase and v-cathepsin genes were deleted from the baculovirus expression vector in a bacmid setup, allowing broad scale application of this novel vector. Deletion of the chitinase and v-cathepsin gene had a positive effect on the integrity of both the intracellular and secreted recombinant protein.

Molecular genetic characterization and subcellular localization of a putative Theileria annulata membrane protein

A Theileria annulata protein (TaD) exhibiting an N-terminal signal sequence for endoplasmic reticulum membrane translocation and a conserved cysteine-rich region was isolated by screening the mRNA of a T. annulata-infected bovine lymphoblastoid cell line with degenerated primers directed against T. annulata-targeting sequences. The TaD-coding sequence was found to be most closely related to the genomic DNA sequence of T. parva (TIGR database, 72%) and the amino acid sequence of Plasmodium falciparum (41%), P. yoelii yoelii (38%) and Cryptosporidium parvum (36%). The TaD mRNA is expressed within the sporozoite, schizont and merozoite stages of the parasite, implying that it is constitutively transcribed throughout the parasite's life cycle. Allelic variants were found between isolates originating from different geographical regions, however not affecting conserved cysteines. The open reading frame encoded a protein of 19.5 kDa and non-reducing SDS-PAGE analysis demonstrated a homodimeric protein. Using confocal microscopy, the protein was found to be both located in the parasite cytoplasm and to colocalize with a transmembrane protein of the schizonts within infected cells.

Improved immunogenicity of novel baculovirus-derived Theileria parva p67 subunit antigens

East Coast fever (ECF) in cattle is caused by the tick-borne protozoan parasite Theileria parva. The major sporozoite surface antigen of T. parva (p67) is an important candidate for inclusion in a subunit vaccine. Recently, we reported the expression and production of different parts of p67 as fusions to either GFP or to the baculovirus GP64 envelope glycoprotein in insect cells, which resulted in stable proteins recognized by a monoclonal specific for native p67. The immunogenicity of these fusion proteins was examined in out-bred mice and cattle. In mice, the full length p67 molecule without its signal peptide and transmembrane region, but fused to GFP (GFP:p67deltaSS) was the best immunogen followed by the C-terminus of p67 fused to GP64 (GP64:p67C). These two immunogens also provoked a high level of sero-conversion in cattle when formulated in a water-in-oil or saponin-derived adjuvant with only 100 microg of protein and a single booster. The vaccine-elicited antibodies efficiently inhibited the infectivity of T. parva sporozoites in in vitro neutralization assays. This study demonstrated that these new baculovirus-derived p67 vaccines were highly immunogenic, and that in combination with a suitable adjuvant, they have a clear potential to induce protective immunity in cattle.

Immunity to East Coast fever in cattle induced by a polypeptide fragment of the major surface coat protein of Theileria parva sporozoites

Full-length recombinant versions of p67, the 709 amino acid major surface protein of Theileria parva sporozoites, induce immunity to East Coast fever (ECF) in cattle. We show that a soluble Escherichia coli recombinant version of p67 (p67(635)), in which a prokaryotic signal peptide replaces the eukaryotic one, confers protection comparable to that induced by the full-length molecule, but is unstable. Peptides encoding 80 (p67C) and 205 (p67N) amino acid fragments of p67, containing epitopes recognised by sporozoite neutralising monoclonal antibodies, exhibit improved stability in E. coli. Antibodies raised against the central region of p67 (p67M) neutralise sporozoite infectivity in vitro. The p67C peptide induced immunity against ECF in cattle, at a level equivalent to p67(635), suggesting that a synthetic peptide vaccine might be achievable.

Evaluation of an enzyme-linked immunosorbent assay with recombinant rhoptry-associated protein 1 antigen against Babesia bovis for the detection of specific antibodies in cattle

The gene encoding Babesia bovis rhoptry-associated protein 1 (RAP-1) was used to develop an enzyme-linked immunosorbent assay (ELISA) to measure specific antibodies against B. bovis. The B. bovis RAP-1 gene was subcloned into a baculovirus transfer vector, and the RAP-1 protein was expressed in insect cells infected with a recombinant baculovirus. The recombinant B. bovis RAP-1 of 65 kDa was detected with anti-RAP-1 mouse serum by Western blotting, and this recombinant RAP-1 was used as an antigen in the ELISA. The ELISA was able to differentiate between B. bovis-infected sera and B. bigemina-infected sera or noninfected normal bovine sera. The results demonstrate that the recombinant RAP-1 expressed in insect cells might be a useful antigen for the detection of antibodies to B. bovis.

Characterization of a polymorphic Theileria annulata surface protein (TaSP) closely related to PIM of Theileria parva: implications for use in diagnostic tests and subunit vaccines

Theileria annulata is a tick-transmitted protozoan that causes tropical theileriosis, an often fatal leukoproliferative disorder of cattle. To characterize and identify parasite proteins suitable as diagnostic antigens and/or vaccine candidates, a cDNA clone encoding a macroschizont stage protein was isolated and characterized (here designated TaSP). The gene, present as a single copy within the parasite genome, is transcribed in the sporozoite and schizont stage and codes for a protein of about 315 amino acids, having a predicted molecular weight of 36 kDa. Allelic variants were found within single parasite isolates and between isolates originating from different geographical regions. The N-terminal part contains a predicted signal peptide and the C-terminal section encodes membrane-spanning regions. Comparison of a number of cDNA clones showed that both these sequence regions are conserved while the central region shows both size and amino acid sequence polymorphism. High identity of the N- and C-terminal regions with the polymorphic immunodominant molecule (PIM) of Theileria parva (identity of 93%), the existence of a central polymorphic region and two short introns within genomic clones suggest that the presented gene/protein may be the T. annulata homologue of PIM. However, the central region of TaSP has no significant identity with PIM, contains no repetitive peptide motifs and is shorter, resulting in a lower molecular weight. The existence of the predicted secretion signal peptide and membrane spanning regions suggest that TaSP is located at the parasite membrane.

Expression of Babesia equi merozoite antigen 1 in insect cells by recombinant baculovirus and evaluation of its diagnostic potential in an enzyme-linked immunosorbent assay

The gene encoding the entire Babesia equi merozoite antigen 1 (EMA-1) was inserted into a baculovirus transfer vector, and a recombinant virus expressing EMA-1 was isolated. The expressed EMA-1 was transported to the surface of infected insect cells, as judged by an indirect fluorescent-antibody test (IFAT). The expressed EMA-1 was also secreted into the supernatant of a cell culture infected with recombinant baculovirus. Both intracellular and extracellular EMA-1 reacted with a specific antibody in Western blots. The expressed EMA-1 had an apparent molecular mass of 34 kDa that was identical to that of native EMA-1. The secreted EMA-1 was used as an antigen in an enzyme-linked immunosorbent assay (ELISA). The ELISA differentiated B. equi-infected horse sera from Babesia caballi-infected horse sera or normal horse sera. The ELISA was more sensitive than the complement fixation test and IFAT. These results demonstrated that the recombinant EMA-1 expressed in insect cells might be a useful diagnostic reagent for detection of antibodies to B. equi.

Immunity and vaccine development in the bovine theilerioses

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

Immunohistochemical detection of parasite antigens in Theileria parva-infected bovine lymphocytes

Theileria parva is the causal agent of East Coast fever (ECF), a fatal disease of cattle characterized by pyrexia, transient lymphadenopathy and panleukopenia. We have evaluated monoclonal antibodies (mAb) against three distinct antigens (p67, PIM and p32) of the parasite as immunohistological reagents for monitoring the kinetics of infection in cattle. Bovine lymphocytes were stained with the mAb at various intervals after infection in vitro and in vivo. The p67 sporozoite surface antigen was detected in only a small percentage of both, in vitro and in vivo infected cells. In contrast, expression of the polymorphic immunodominant molecule (PIM) of the parasite proved a useful indicator of infection and staining was correlated with the results of Giemsa analysis. PIM was detected from day 3 in in vitro-infected cells, but was not detected until day 5 in vivo after challenge with a 70% lethal dose of stabilized sporozoite. The p32 antigen was expressed only late in infection in vivo and its expression was associated with the development of merozoites. Less than 20% of in vitro-infected cells expressed p32. The immunohistochemical staining with anti-PIM mAb was found to be a useful tool for analysis of T. parva infection kinetics in cattle.

Control of coccidiosis: lessons from other sporozoa

Coccidiosis is the most important parasitic infection in poultry worldwide and also causes problems in cattle, sheep and goats. Control is largely limited to good husbandry and prophylactic chemotherapy using a range of drugs against which resistance is rapidly acquired. Attempts at vaccination using conventional vaccines have been disappointing and there is now a need for a new approach. Research into the immunology of coccidiosis has lagged behind that of other sporozoans and there are useful lessons that might be learned from studies on toxoplasmosis, cryptosporidiosis, theileriosis and malaria. In these infections the emphasis has turned to the cytokine network that drives the response towards protection. Central to these studies are the roles of interferon-gamma, interleukin-12 and activated macrophages with the involvement of nitric oxide in parasite killing. Cytotoxic T cells have also increasingly been implicated. Research has shown that different immune responses can be elicited by manipulating the cytokine system and these new concepts can be applied to the design of peptide or recombinant vaccines, and the possibilities of developing such vaccines against coccidiosis will be discussed.

Detection of Theileria sergenti schizonts in bovine lymph node

The growth of Theileria sergenti schizonts in bovine lymph nodes was examined by experimental infection. Six naive Holstein calves were inoculated with a sporozoite stabilate into the superficial cervical and subiliac lymph nodes. Biopsy samples from the inoculated calves were collected every 24 h for 10 days. Histological examination demonstrated the schizont of T. sergenti on day 4 post-inoculation. The growth of schizonts in the lymph node was observed on days 4-8 post-inoculation. Electron microscopic observation disclosed that the core of the schizont has a high density central core surrounded by numerous electron-dense spherules.

Conservation of the sporozoite p67 vaccine antigen in cattle-derived Theileria parva stocks with different cross-immunity profiles

Immunity to Theileria parva infection in cattle is often parasite stock specific. The antigenic diversity which is expressed at the schizont stage of the parasite together with a wild reservoir of the organism in buffalo has complicated the development of effective disease control by immunization. We have previously shown that about 70% of cattle inoculated with recombinant forms of p67, a sporozoite stage-specific surface antigen from the cattle-derived Muguga stock of the parasite, are immune to a homologous challenge. Thus, immune responses to p67 can play a role in immunity. The genes encoding this protein in five other parasite stocks have been sequenced. Here, we report that the p67 molecule encoded by four cattle-derived parasite stocks (Boleni, Uganda, Mariakani, and Marikebuni) that fall into different cross-immunity groups is identical in sequence to Muguga p67. The protein encoded by a buffalo-derived parasite exhibits 95% sequence identity with Muguga p67, the major difference being the presence of a 43-residue peptide insert. As predicted by these data, cattle inoculated with recombinant p67 can resist a heterologous cattle-derived parasite challenge. Seven of 12 cattle receiving a homologous Muguga challenge and 6 of 11 cattle receiving a heterologous Marikebuni challenge were immune to East Coast fever. These results extend earlier data suggesting that p67 is a conserved molecule and confirm its potential as a broad-spectrum vaccine antigen for the control of T. parva infection.