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

p67 gene alleles sequence analysis reveals Theileria parva parasites associated with East Coast fever and Corridor disease in buffalo from Zambia

Theileriosis caused by Theileria parva infections is responsible for high cattle mortalities in Zambia. Although infected buffalo are a risk to cattle, the characterization of T. parva parasites occurring in this host in Zambia has not been reported. Furthermore, considering the advances in the development of a p67 subunit vaccine, the knowledge of p67 genetic and antigenic diversity in both cattle and buffalo associated T. parva is crucial. Therefore, blood samples from buffalo (n=43) from Central, Eastern and Southern provinces, and cattle (n=834) from Central, Copperbelt, Eastern, Lusaka, and Southern provinces, were tested for T. parva infection and the parasites characterized by sequencing the gene encoding the p67 antigen. About 76.7 % of buffalo and 19.3 % of cattle samples were PCR positive for T. parva. Three of the four known p67 allele types (1, 2 and 3) were identified in parasites from buffalo, of which two (allele types 2 and 3) are associated with T. parva parasites responsible for Corridor disease. Only allele type 1, associated with East Coast fever, was identified from cattle samples, consistent with previous reports from Zambia. Phylogenetic analysis revealed segregation between allele type 1 sequences from cattle and buffalo samples as they grouped separately within the same sub-clade. The high occurrence of T. parva infection in buffalo samples investigated demonstrates the risk of Corridor disease infection, or even outbreaks, should naïve cattle co-graze with infected buffalo in the presence of the tick vector. In view of a subunit vaccine, the antigenic diversity in buffalo associated T. parva should be considered to ensure broad protection. The current disease control measures in Zambia may require re-evaluation to ensure that cattle are protected against buffalo-derived T. parva infections. Parasite stocks used in 'infection and treatment' immunization in Zambia, have not been evaluated for protection against buffalo-derived T. parva parasites currently circulating in the buffalo population.

Systematic Determination of TCR–Antigen and Peptide–MHC Binding Kinetics among Field Variants of a Theileria parva Polymorphic CTL Epitope

Positions 1–3 in the Tp9 CTL epitope are required for binding to BoLA-1*023:01.

Positions 5–8 in the Tp9 epitope are required for TCR recognition in diverse CTLs.

Tp9-specific CTLs from Muguga-immunized animals can cross-react with variants 4 and 7.

CTLs are known to contribute to immunity toward Theileria parva, the causative agent of East Coast fever. The Tp9_67–75 CTL epitope from the Muguga strain of T. parva is polymorphic in other parasite strains. Identifying the amino acids important for MHC class I binding, as well as TCR recognition of epitopes, can allow the strategic selection of Ags to induce cellular immunity toward T. parva. In this study, we characterized the amino acids important for MHC class I binding and TCR recognition in the Tp9_67–75 epitope using alanine scanning and a series of variant peptide sequences to probe these interactions. In a peptide–MHC class I binding assay, we found that the amino acids at positions 1, 2, and 3 were critical for binding to its restricting MHC class I molecule BoLA-1*023:01. With IFN-γ ELISPOT and peptide–MHC class I Tet staining assays on two parasite-specific bovine CTL lines, we showed that amino acids at positions 5–8 in the epitope were required for TCR recognition. Only two of eight naturally occurring polymorphic Tp9 epitopes were recognized by both CTLs. Finally, using a TCR avidity assay, we found that a higher TCR avidity was associated with a stronger functional response toward one of two variants recognized by the CTL. These data add to the growing knowledge on the cross-reactivity of epitope-specific CTLs and specificities that may be required in the selection of Ags in the design of a wide-spectrum vaccine for East Coast fever.

Babesia microti Immunoreactive Rhoptry-Associated Protein-1 Paralogs Are Ancestral Members of the Piroplasmid-Confined RAP-1 Family

Babesia, Cytauxzoon and Theileria are tick-borne apicomplexan parasites of the order Piroplasmida, responsible for diseases in humans and animals. Members of the piroplasmid rhoptry-associated protein-1 (pRAP-1) family have a signature cysteine-rich domain and are important for parasite development. We propose that the closely linked B. microti genes annotated as BMR1_03g00947 and BMR1_03g00960 encode two paralogue pRAP-1-like proteins named BmIPA48 and Bm960. The two genes are tandemly arranged head to tail, highly expressed in blood stage parasites, syntenic to rap-1 genes of other piroplasmids, and share large portions of an almost identical ~225 bp sequence located in their 5' putative regulatory regions. BmIPA48 and Bm960 proteins contain a N-terminal signal peptide, share very low sequence identity (<13%) with pRAP-1 from other species, and harbor one or more transmembrane domains. Diversification of the piroplasmid-confined prap-1 family is characterized by amplification of genes, protein domains, and a high sequence polymorphism. This suggests a functional involvement of pRAP-1 at the parasite-host interface, possibly in parasite adhesion, attachment, and/or evasion of the host immune defenses. Both BmIPA48 and Bm960 are recognized by antibodies in sera from humans infected with B. microti and might be promising candidates for developing novel serodiagnosis and vaccines.

Flow Cytometric Analysis of the Cytotoxic T-Cell Recall Response to Theileria parva in Cattle Following Vaccination by the Infection and Treatment Method

The apicomplexan hemoparasite, Theileria parva, causes East Coast fever (ECF), a frequently fatal disease of African cattle. Vaccine development has been impeded by incomplete understanding of protective immunity following natural exposure or the infection and treatment method (ITM) of immunization. This is attributable to a paucity of methods to characterize the memory T-cell repertoire following infection. To overcome this impediment, assays developed to study the immune response to other intracellular pathogens were adapted for use in studies with T. parva to enable definition of the phenotype and function of effector T cells in T. parva-immune cattle, facilitating vaccine development. As reported herein, stimulation of peripheral blood mononuclear cells (PBMC) from ITM-immunized steers with irradiated, autologous, T. parva-infected cell lines elicited a proliferative recall response comprised of CD45R0⁺/CCR7⁻ CD4⁺ and CD8⁺ T cells. Subsequent co-incubation of stimulated cultures with infected cells demonstrated the presence of cytotoxic T cells (CTLs) with the ability to kill infected cells. Comparison of CTL activity in cultures depleted of CD4⁺ or CD8⁺ T cells demonstrated CTL activity was primarily attributed to CD8⁺ T cells. Importantly, stimulation of PBMC from vaccinated steers always elicited proliferation of CD4⁺ and CD8⁺ T cells. This was the first important observation obtained from the use of the assay described herein.

Limited diversity in the CD8+ antigen-coding loci in Theileria parva parasites from cattle from southern and eastern Africa

Theileria parva infections in cattle causes huge economic losses in the affected African countries, directly impacting the livelihood of the poor small-holder farmers. The current immunization protocol using live sporozoites in eastern Africa, is among the control measures designed to limit T. parva infections in cattle. However, the ability of the immune protection induced by this immunization to protect against field parasites has been compromised by the diversity of the parasite involving the schizont antigen genes. Previous studies have reported on the antigenic diversity of T. parva parasites from southern and eastern Africa, however, similar reports on T. parva parasites particularly from cattle from southern Africa remains scanty, due to the self-limiting nature of Corridor disease. Thus, we evaluated the diversity of CD8+ T-cell regions of ten schizont antigen genes in T. parva parasites associated with Corridor disease and East Coast fever (ECF) from southern and eastern Africa respectively. Regions of schizont antigen (TpAg) genes containing the CD8+ T-cell epitopes (CTL determinants) were amplified from genomic DNA extracted from blood of T. parva positive samples, cloned and sequenced. The results revealed limited diversity between the two parasite groups from cattle from southern and eastern Africa, defying the widely accepted notion that antigen-encoding loci in cattle-derived parasites are conserved, while in buffalo-derived parasites, they are extensively variable. This suggests that only a sub-population of parasites is successfully transmitted from buffalo to cattle, resulting in the limited antigenic diversity in Corridor disease parasites. Tp4, Tp5, Tp7 and Tp8 showed limited to absence of diversity in both parasite groups, suggesting the need to further investigate their immunogenic properties for consideration as candidates for a subunit vaccine. Distinct and common variants of Tp2 were detected among the ECF parasites from eastern Africa indicating evidence of parasite mixing following immunization. This study provides additional information on the comparative diversity of TpAg genes in buffalo- and cattle-derived T. parva parasites from cattle from southern and eastern Africa.

Clinical Pathology, Immunopathology and Advanced Vaccine Technology in Bovine Theileriosis: A Review

Theileriosis is a blood piroplasmic disease that adversely affects the livestock industry, especially in tropical and sub-tropical countries. It is caused by haemoprotozoan of the Theileria genus, transmitted by hard ticks and which possesses a complex life cycle. The clinical course of the disease ranges from benign to lethal, but subclinical infections can occur depending on the infecting Theileria species. The main clinical and clinicopathological manifestations of acute disease include fever, lymphadenopathy, anorexia and severe loss of condition, conjunctivitis, and pale mucous membranes that are associated with Theileria-induced immune-mediated haemolytic anaemia and/or non-regenerative anaemia. Additionally, jaundice, increases in hepatic enzymes, and variable leukocyte count changes are seen. Theileria annulata and Theileria parva induce an incomplete transformation of lymphoid and myeloid cell lineages, and these cells possess certain phenotypes of cancer cells. Pathogenic genotypes of Theileria orientalis have been recently associated with severe production losses in Southeast Asia and some parts of Europe. The infection and treatment method (ITM) is currently used in the control and prevention of T. parva infection, and recombinant vaccines are still under evaluation. The use of gene gun immunization against T. parva infection has been recently evaluated. This review, therefore, provides an overview of the clinicopathological and immunopathological profiles of Theileria-infected cattle and focus on DNA vaccines consisting of plasmid DNA with genes of interest, molecular adjuvants, and chitosan as the most promising next-generation vaccine against bovine theileriosis.