Characterization of the gene encoding the polymorphic immunodominant molecule, a neutralizing antigen of Theileria parva

Theileria parva, a tick-transmitted protozoan parasite related to Plasmodium spp., causes the disease East Coast fever, an acute and usually fatal lymphoproliferative disorder of cattle in Africa. Previous studies using sera from cattle that have survived infection identified a polymorphic immunodominant molecule (PIM) that is expressed by both the infective sporozoite stage of the parasite and the intracellular schizont. Here we show that mAb specific for the PIM Ag can inhibit sporozoite invasion of lymphocytes in vitro. A cDNA clone encoding the PIM Ag of the T. parva (Muguga) stock was obtained by using these mAb in a novel eukaryotic expression cloning system that allows isolation of cDNA encoding cytoplasmic or surface Ags. To establish the molecular basis of the polymorphism of PIM, the cDNA of the PIM Ag from a buffalo-derived T. parva stock was isolated and its sequence was compared with that of the cattle-derived Muguga PIM. The two cDNAs showed considerable identity in both the 5' and 3' regions, but there was substantial sequence divergence in the central regions. Several types of repeated sequences were identified in the variant regions. In the Muguga form of the molecule, there were five tandem repeats of the tetrapeptide, QPEP, that were shown, by transfection of a deleted version of the PIM gene, not to react with several anti-PIM mAbs. By isolating and sequencing the genomic version of the gene, we identified two small introns in the 3' region of the gene. Finally, we showed that polyclonal rat Abs against recombinant PIM neutralize sporozoite infectivity in vitro, suggesting that the PIM Ag should be evaluated for its capacity to immunize cattle against East Coast Fever.

Characterization of the gene encoding the polymorphic immunodominant molecule, a neutralizing antigen of Theileria parva

Theileria parva, a tick-transmitted protozoan parasite related to Plasmodium spp., causes the disease East Coast fever, an acute and usually fatal lymphoproliferative disorder of cattle in Africa. Previous studies using sera from cattle that have survived infection identified a polymorphic immunodominant molecule (PIM) that is expressed by both the infective sporozoite stage of the parasite and the intracellular schizont. Here we show that mAb specific for the PIM Ag can inhibit sporozoite invasion of lymphocytes in vitro. A cDNA clone encoding the PIM Ag of the T. parva (Muguga) stock was obtained by using these mAb in a novel eukaryotic expression cloning system that allows isolation of cDNA encoding cytoplasmic or surface Ags. To establish the molecular basis of the polymorphism of PIM, the cDNA of the PIM Ag from a buffalo-derived T. parva stock was isolated and its sequence was compared with that of the cattle-derived Muguga PIM. The two cDNAs showed considerable identity in both the 5' and 3' regions, but there was substantial sequence divergence in the central regions. Several types of repeated sequences were identified in the variant regions. In the Muguga form of the molecule, there were five tandem repeats of the tetrapeptide, QPEP, that were shown, by transfection of a deleted version of the PIM gene, not to react with several anti-PIM mAbs. By isolating and sequencing the genomic version of the gene, we identified two small introns in the 3' region of the gene. Finally, we showed that polyclonal rat Abs against recombinant PIM neutralize sporozoite infectivity in vitro, suggesting that the PIM Ag should be evaluated for its capacity to immunize cattle against East Coast Fever.

Characterization of a polymorphic immunodominant molecule in sporozoites and schizonts of Theileria parva

This study examines several aspects of a polymorphic, immunodominant molecule (PIM) found in the protozoan parasite, Theileria parva. The antigen is present in all T.p. parva stocks examined, and in the related subspecies, T.p.bovis and T.p.lawrencei. It is the predominant antigen recognized by antisera from immune cattle on Western blot analysis of schizont-infected lymphocytes, and is the only antigen which has been shown to react with anti-schizont monoclonal antibodies (MoAbs) on Western blots or in immunoprecipitations. The antigen shows polymorphism in both size and expression of antibody epitopes among the different stocks of T. parva. The antigen is present in sporozoites as well as schizonts.

Identification of a bovine surface antigen uniquely expressed on CD4-CD8- T cell receptor gamma/delta+ T lymphocytes

In this study, two monoclonal antibodies, IL-A29 and CC15, are described that identify a novel bovine cell surface marker of 215/300 kDa. The antibodies reacted with a discrete population of resting lymphocytes in peripheral blood which, in young animals, constituted about 25% of the mononuclear cells. Thymus, lymph nodes and spleen contained less than 5% positive cells. These cells were negative for surface Ig, a monocyte/granulocyte marker, and the T lymphocyte antigens CD2, CD6, CD4 and CD8. Immunohistological analyses revealed the presence of IL-A29/CC15-positive lymphocytes in the thymic medulla, in the outer cortex of lymph nodes, in the marginal zones of the spleen, in the dermal and epidermal layers of the skin and in the lamina propria of the gut. The IL-A29/CC15+ cells in unfractionated blood mononuclear cells responded in autologous and allogeneic mixed lymphocyte cultures, and when purified they responded to concanavalin A in the presence of recombinant interleukin 2. These observations suggested this population of cells belonged to the T cell lineage. In order to unambiguously define their lineage, cDNA clones encoding bovine T cell receptor (TcR) and CD3 proteins were isolated. Northern blot analyses of IL-A29/CC15+ cell populations and of established cell lines of various lineages demonstrated that they expressed TcR delta and CD3 gamma, delta and epsilon mRNA: TcR alpha was not expressed, whereas only a truncated form of TcR beta mRNA was present. These results indicate that the IL-A29 and CC15 antibodies define a unique population of CD4-CD8-, gamma/delta T cells.

Improved characterization of Theileria parva isolates using the polymerase chain reaction and oligonucleotide probes

Theileria parva DNA was purified from piroplasms isolated from cattle infected with 5 different East African isolates of the parasite, including the East Coast fever reference stock T. p. parva Muguga. Total cellular DNA was prepared from T. parva schizont-infected bovine lymphoblastoid cell cultures (11 isolates). Two probes, previously isolated from T. p. parva Muguga repetitive genomic DNA, were hybridized to restriction digests; closely similar restriction fragment length polymorphism (RFLP) patterns were produced, and no two isolates had the same RFLP pattern. The DNA sequences of probe PMB3, two further copies of the repeated sequence from T. p. parva Muguga, and homologous regions from T. p. parva Kiambu 4 and T. p. lawrencei 3081, were determined. Oligonucleotides were synthesized corresponding to two conserved sections flanking a region which varied between isolates. These oligonucleotides were used as primers in the polymerase chain reaction to amplify the variable region. Further oligonucleotides corresponding to sequences in this variable region were able to distinguish between isolates and no sample hybridized to both oligonucleotides. This is the first unequivocal plus/minus discrimination between groups of isolates to be achieved for T. parva.

DNA probes detect genomic diversity in Theileria parva stocks

Different stocks of Theileria parva were analysed for restriction fragment length polymorphisms by agarose gel electrophoresis, orthogonal-field-alternation gel electrophoresis (OFAGE) and Southern hybridization with DNA probes. Polymorphisms seen with DNA from purified piroplasms of different T. parva stocks, after digestion with restriction enzymes, were more clearly apparent with OFAGE than with standard agarose gel electrophoresis. Genomic differences between these theilerial parasites were investigated further using three DNA probes, which were selected from a genomic library of T. parva (Muguga) piroplasm DNA cloned in lambda gt11. All three clones hybridized to T. parva DNA in preparations from schizont-infected bovine lymphoblastoid cells and to DNA from intraerythrocytic piroplasms. These probes did not, however, hybridize under high stringency conditions to DNA prepared from uninfected bovine lymphoblasts, T. mutans piroplasms, or bovine lymphoblasts infected with T. annulata or T. taurotragi. The five Kenyan stocks of T. parva that were tested showed characteristic hybridization patterns with these DNA probes. Our results show that DNA probes can be used to distinguish selected stocks of T. parva by hybridization to DNA either from intraerythrocytic piroplasms taken from infected cattle, or from isolates of schizont-infected bovine lymphoblastoid cells that are maintained continuously in vitro.