Novel immunization strategies against protozoan parasites. Proceedings of a workshop

The main aim of this meeting was to review those developments in the fields of immunology and immunoparasitology that have relevance to the development of vaccination strategies for ECF and trypanosomiasis. Of relevance to the control of ECF were recent developments in the elucidation of events that surround the induction of cytotoxic T lymphocytes, and the role of cytokines in the control and pathogenesis of parasitic infections. Chief areas of interest to the trypanosomiasis programme were disease-related perturbations of the immune system, the role of individual T cell subsets in immunity to parasites and the involvement of cytokines in the control and pathogenesis of parasitic diseases. More specific discussions focused on the role of CTL in parasitic infections; antigen processing for class I MHC - restricted responses; novel technologies for identifying antigens that provoke CTL responses; the role of detrimental immune responses in pathogenesis; the role of T cell subsets and their products in the control of parasitic diseases; and immunization strategies for driving immune responses towards favourable rather than detrimental mechanisms

Zoonoses (Project 1): Wildlife/domestic livestock interactions

The objective of this study was to synthesise the best available scientific knowledge about zoonotic disease transmission through livestock and wildlife interaction (direct or indirect), with emphasis on risk factors, drivers and trajectories of transmission, as well as promising interventions for controlling important zoonoses, based on managing the interaction between domestic livestock and wildlife. A multi-disciplinary team from the International Livestock Research Institute, Kenya, and the Royal Veterinary College, United Kingdom, with expertise in zoonoses, epidemiology, socio-economics, and wildlife, undertook the review. A database of important zoonoses was compiled and used to develop a list of priority zoonoses with a livestock-wildlife interface for developing countries. Spatial relationships between important zoonoses and land use and human population density were explored. A systematic review was carried out focussing on: disease transmission routes, risk factors for disease transmission, drivers of wildlife-livestock interactions, pathogens of wildlife capable of recombining with organisms in livestock, wildlife species that are potential sources of zoonotic pathogens, production and socio-economic factors influencing the risk of transmission, and risk management and control interventions

Expression Analysis of the Theileria parva Subtelomere-Encoded Variable Secreted Protein Gene Family

Background The intracellular protozoan parasite Theileria parva transforms bovine lymphocytes inducing uncontrolled proliferation. Proteins released from the parasite are assumed to contribute to phenotypic changes of the host cell and parasite persistence. With 85 members, genes encoding subtelomeric variable secreted proteins (SVSPs) form the largest gene family in T. parva. The majority of SVSPs contain predicted signal peptides, suggesting secretion into the host cell cytoplasm. Methodology/Principal Findings We analysed SVSP expression in T. parva-transformed cell lines established in vitro by infection of T or B lymphocytes with cloned T. parva parasites. Microarray and quantitative real-time PCR analysis revealed mRNA expression for a wide range of SVSP genes. The pattern of mRNA expression was largely defined by the parasite genotype and not by host background or cell type, and found to be relatively stable in vitro over a period of two months. Interestingly, immunofluorescence analysis carried out on cell lines established from a cloned parasite showed that expression of a single SVSP encoded by TP03_0882 is limited to only a small percentage of parasites. Epitope-tagged TP03_0882 expressed in mammalian cells was found to translocate into the nucleus, a process that could be attributed to two different nuclear localisation signals. Conclusions Our analysis reveals a complex pattern of Theileria SVSP mRNA expression, which depends on the parasite genotype. Whereas in cell lines established from a cloned parasite transcripts can be found corresponding to a wide range of SVSP genes, only a minority of parasites appear to express a particular SVSP protein. The fact that a number of SVSPs contain functional nuclear localisation signals suggests that proteins released from the parasite could contribute to phenotypic changes of the host cell. This initial characterisation will facilitate future studies on the regulation of SVSP gene expression and the potential biological role of these enigmatic proteins

Trans-Species Polymorphism and Selection in the MHC Class II DRA Genes of Domestic Sheep

Highly polymorphic genes with central roles in lymphocyte mediated immune surveillance are grouped together in the major histocompatibility complex (MHC) in higher vertebrates. Generally, across vertebrate species the class II MHC DRA gene is highly conserved with only limited allelic variation. Here however, we provide evidence of trans-species polymorphism at the DRA locus in domestic sheep (Ovis aries). We describe variation at the Ovar-DRA locus that is far in excess of anything described in other vertebrate species. The divergent DRA allele (Ovar-DRA*0201) differs from the sheep reference sequences by 20 nucleotides, 12 of which appear non-synonymous. Furthermore, DRA*0201 is paired with an equally divergent DRB1 allele (Ovar-DRB1*0901), which is consistent with an independent evolutionary history for the DR sub-region within this MHC haplotype. No recombination was observed between the divergent DRA and B genes in a range of breeds and typical levels of MHC class II DR protein expression were detected at the surface of leukocyte populations obtained from animals homozygous for the DRA*0201, DRB1*0901 haplotype. Bayesian phylogenetic analysis groups Ovar-DRA*0201 with DRA sequences derived from species within the Oryx and Alcelaphus genera rather than clustering with other ovine and caprine DRA alleles. Tests for Darwinian selection identified 10 positively selected sites on the branch leading to Ovar-DRA*0201, three of which are predicted to be associated with the binding of peptide antigen. As the Ovis, Oryx and Alcelaphus genera have not shared a common ancestor for over 30 million years, the DRA*0201 and DRB1*0901 allelic pair is likely to be of ancient origin and present in the founding population from which all contemporary domestic sheep breeds are derived. The conservation of the integrity of this unusual DR allelic pair suggests some selective advantage which is likely to be associated with the presentation of pathogen antigen to T-cells and the induction of protective immunity

Multi-component subunit vaccines against Theileria parva

Cattle that recover from Theileria parva infection are solidly immune to rechallenge with homologous parasites. Most of the ILRAD/ILRI immunological research into the disease has focused on defining the basis of this protection. Over 15 years of basic and applied immunological research at ILRAD/ILRI have demonstrated that protection in T. parva immune cattle is primarily mediated by parasite-specific Cytotoxic T. lymphocytes (CTL). This paper summarises the status of the research and options including antigens, in vivo activation requirements and antigen delivery systems

Vaccines and diagnostic tools for animal health: The influence of biotechnology

Development of improved vaccine and diagnostic-based disease control strategies has benefited considerably from advances in biotechnology, particularly those relating to recombinant DNA technology. Efficiency of the vaccine development process has been increased at all levels, from the analysis of immune responses to the production and delivery of protective antigens to the target species. Serological analysis of antibody prevalence has also become more straightforward as a result of the availability of recombinant pathogen proteins. However, greatest advances arising from biotechnological development relate to the detection and characterisation of pathogens in infected hosts. Probably the most significant development in this regard, which impacts both vaccine and diagnostic development, is the polymerase chain reaction. With the advent of DNA-based antigen delivery vehicles, it is conceivable that protein-based vaccine and diagnostic systems will have been superseded by DNA-based systems by the middle of the 21st century