A cell surface antigen associated with Theileria parva lawrencei-infected bovine lymphoid cells

Characterization of some Theileria parva stocks from Zambia using monoclonal antibodies

Theileria parva parasites have been isolated from different location in Zambia where malignant theileriosis has been recorded. A total of 16 bovine lymphocytic cell lines infected with T. parva schizonts were characterized using a panel of anti-schizont monoclonal antibodies (MAbs). Comparison of the Theileria stocks isolated before (old) and after (new) the Muguga cocktail of T. parva from Kenya was used to vaccinate cattle against theileriosis in Zambia revealed differences in their reactivity against MAbs. The new isolates are showing MAb profiles similar to that exhibited by the Muguga cocktail which was used to vaccinate cattle in these areas between 1983 and 1989. These results suggest that the use of the Muguga cocktail to vaccinate animals against theileriosis in Zambia may have introduced Theileria stocks of different antigenic properties.

Identification of neutralization and diagnostic epitopes on PIM, the polymorphic immunodominant molecule of Theileria parva

The polymorphic immunodominant molecule (PIM) of Theileria parva is expressed by the schizont and sporozoite stages of the parasite. We have recently cloned the cDNA encoding the PIM antigen from two stocks of the parasite: the cattle-derived T. parva (Muguga) stock and a buffalo-derived stock. The cDNAs were used in transient-transfection assays to assess the reactivity of the antigen with monoclonal antibodies (MAb) previously raised against schizont-infected cells and used for parasite strain identification. We demonstrate that 19 of the 25 MAb are specific for PIM. Antibody reactivities with deletion mutants of a fusion protein containing PIM and Pepscan analysis of the Muguga version of the molecule with 13 of the MAb indicate that there are at least 10 different epitopes throughout the molecule. None of the MAb react with a tetrapeptide repeat present in the central region of the molecule, probably because of an inability of BALB/c mice to produce antibodies to this repeat. In contrast, sera from infected cattle react strongly with the repeat region, suggesting that this region alone may be useful as a diagnostic reagent. Previous studies showed that MAb to PIM inhibit sporozoite infectivity of bovine lymphocytes in vitro, which suggests that the antigen may be useful in immunizing cattle against T. parva infection. Pepscan analysis revealed that sera from infected cattle reacted with peptides recognized by the neutralizing MAb, as did sera from cattle inoculated with a PIM-containing recombinant protein. The latter sera did not, however, neutralize sporozoite infectivity in vitro. These results will be useful in exploiting the strain identification, diagnostic, and immunizing potentials of this family of antigens.

Theileria parva: CD4+ helper and cytotoxic T-cell clones react with a schizont-derived antigen associated with the surface of Theileria parva-infected lymphocytes

Theileria parva is a protozoan parasite which infects and transforms bovine lymphocytes, resulting in a fatal lymphoproliferative disease. There is evidence that immunity to the intralymphocytic schizont stage is mediated by T cells. We have previously reported derivation of CD4+ T-cell clones which recognize parasite-derived antigens presented on the surface of infected cells in conjunction with MHC molecules and partial characterization of the antigens. The present study further evaluated one of these antigens, demonstrating that it could be derived from cells infected with different parasite stocks as well as from purified theilerial schizonts and that it was recognized by primed, but not unprimed, bovine lymphocytes including cytolytic CD4+ T cells. Using a cloned CD4+ cytolytic cell line, lysis of schizont-infected cells was shown to be MHC-restricted but not parasite-strain restricted. In addition we demonstrated that T cells which respond to the HSS antigen preparation were generated in cattle immunized with parasites from any of the three subspecies of T. parva. The antigenic material was fractionated by sequential subjection to anion-exchange chromatography, hydroxylapatite chromatography, and gel filtration using HPLC, which resulted in recovery of approximately 20% of the antigenic material with more than 10(6)-fold purification in selected fractions. To assess the molecular size of the proteins in the highly purified antigenic fractions, the T. parva-infected lymphocytes were metabolically labeled before fractionation with 3H-amino acids and the material was analyzed by SDS-polyacrylamide gel electrophoresis and liquid scintillation counting of gel slices. The major protein in these fractions had a molecular mass of 9-10 kDa.

Immunization with Theileria parva parasites from buffaloes results in generation of cytotoxic T cells which recognize antigens common among cells infected with stocks of T. parva parva, T. parva bovis, and T. parva lawrencei

Immunity to infection by the protozoan parasite Theileria parva in cattle is partially attributable to cytotoxic T cells, which kill lymphocytes infected with the schizont stage of the parasite. Here we evaluated five stocks of buffalo-derived T. parva lawrencei parasites and two stocks of cattle-derived T. parva parva parasites for their ability to induce in vivo cytotoxic T cells which can kill lymphocytes infected with a wide variety of strains of T. parva parasites. A group of seven full-sibling cattle, produced by embryo transfer and matched for at least one major histocompatibility complex class I haplotype, were immunized by infection and treatment with the parasite stocks. Target cells used in in vitro cytotoxicity assays were infected with five buffalo-derived parasite stocks and five cattle-derived parasite stocks, including T. parva parva and T. parva bovis. Immunization with any of the seven parasite stocks resulted in the generation of cytotoxic T cells which recognized parasite antigens on most if not all of the target cell lines tested, although the T. parva bovis stock was the least effective at doing so. Further in-depth analyses performed with peripheral blood mononuclear cells from one of the cattle immunized with T. parva lawrencei parasites showed that the pattern of killing of the panel of target cells was altered when either cells infected with different parasite stocks or clones of infected cells were used as stimulator cells in vitro, suggesting the presence of more than one population of parasite-specific cytotoxic effector cells in the peripheral blood mononuclear cells. However, clones of these cytotoxic effector cells recognized common or cross-reactive antigen epitopes expressed by the entire panel of infected target cells. These T-cell clones will be useful for identifying common T-cell antigen epitopes of T. parva and the parasite genes encoding them.

Theilerial parasites isolated from carrier cattle after immunization with Theileria parva by the infection and treatment method

Groups of cattle were immunized with 10(-2) dilutions of sporozoite stabilates of Theileria parva lawrencei derived from African buffaloes either alone or in combination with Theileria parva parva derived from cattle and concomitant treatment with either long or short-acting formulations of oxytetracyline. At 90 or 120 days after infection, uninfected Rhipicephalus appendiculatus nymphal ticks were applied to individual immunized cattle and the resultant adults ticks were applied to individual susceptible cattle. Theilerial infection developed from ticks fed on 6 out of 11 animals investigated for evidence of a carrier state. Two additional animals were shown by cell-culture isolation to have persistent theilerial infections. Nine cattle infected with the parasites from carrier animals were treated with paravaquone and 7 recovered. These recovered cattle were then challenged with the original immunizing stabilates at 10 degrees dilution together with the original immunized and carrier cattle. Six out of 7 cattle which had recovered from carrier-derived infection succumbed to this challenge and died but none of the original immunized cattle showed theilerial reactions. When a carrier-derived sporozoite stabilate was used to challenge cattle immune to the original immunizing parasite, they proved to be immune. Cattle immune to the carrier-derived parasites were all immune to challenge with the original parasite. A monoclonal antibody profile against T. parva schizonts isolated by cell culture from samples of the experimental animals did not appear to be sensitive enough to determine the antigenic differences between the carrier-derived parasite and the original immunizing parasite. Indications are that the carrier state is not likely to produce new antigenic strains which would be dangerous to immunized cattle.

Isolation and characterization of RNA from the intracellular parasite Theileria parva

Using a rapid procedure to isolate schizonts of the intracellular parasite Theileria parva from infected bovine lymphocytes, we have prepared parasite RNA that is more than 90% pure. Characterization of this schizont RNA has revealed the presence of two ribosomal RNA species of 3.3 kb and 1.8 kb and a third non-adenylated abundant RNA species of 1.9 kb. In vitro translation of the isolated schizont mRNA has identified about 200 parasite specific polypeptides, only a few of which could be detected by translation of mRNA from infected host cells. By analysing the kinetics of liquid hybridization of schizont mRNA with its homologous complementary DNA the nucleotide sequence complexity of the abundant class of the parasite mRNA has been estimated to be 1.7 x 10(3) kb. Assuming a number average size of 2 kb per mRNA molecule this would represent 4000 transcripts for all abundance classes of the schizont mRNA. Using the same technique we estimate that approximately 10% of the mRNA isolated from infected lymphocytes were transcripts from the parasite genome. We conclude that the low number of parasite specific translation products in the mRNA from infected lymphocytes and the low number of parasite proteins detected in isolated schizonts reported previously is due to the low abundance of the parasite transcripts rather than a low number of expressed parasite genes.

Immunological control of ticks and tick-borne parasitic diseases of livestock

Parasitic diseases inflict major losses on livestock production throughout the world. Currently, control of the diseases relies largely on prophylactic or therapeutic application of anti-parasitic drugs. In many instances, these measures are only partially effective. Moreover, they must be applied frequently, are therefore costly and time-consuming, and lead to the selection of drug resistance within the parasite populations. Thus, it has been recognized for several decades that effective methods of vaccination against parasitic diseases would have a major impact on livestock production. However, despite considerable efforts over the last 30 years, only a few parasite vaccines are currently in use and all of these involve the administration of live organisms.

Theileria parva infection induces autocrine growth of bovine lymphocytes

Bovine lymphocytes infected with the parasite Theileria parva continuously secrete a growth factor that is essential for their proliferation in vitro and also constitutively express interleukin 2 receptors on their surface. Dilution of the secreted growth factor, caused by culturing cells at low density, results in retardation of culture growth. Human recombinant interleukin 2, however, effectively substitutes for the diluted growth factor by restoring normal growth rates and also allows Theileria-infected cells to be grown at low density without the use of feeder layers. Secretion of the growth factor and expression of the interleukin 2 receptor depend on the presence of the parasite in the cytoplasm of the host cell. Elimination of the parasite from the cell cytoplasm by the specific antitheilerial drug BW 720c results in the arrest of growth factor secretion and the disappearance of interleukin 2 receptors from the cell surface. This is accompanied by growth arrest and reversion of the infected cells to the morphology of resting lymphocytes. We propose that the continuous proliferation of infected cells in vitro is mediated by autocrine receptor activation.

Bovine T cells, B cells, and null cells are transformed by the protozoan parasite Theileria parva

The target cells for infection and transformation by Theileria parva were investigated. Peripheral blood mononuclear cells were reacted with monoclonal antibodies specific for bovine leukocyte differentiation antigens, sorted into subpopulations with a fluorescence-activated cell sorter, and infected in vitro with T. parva sporozoites. Infected cells were cultured at limiting dilution, and transformed clones were screened with monoclonal antibodies. The results indicated that B cells, T cells (including BoT4+ and BoT8+ cells), and null cells but not monocytes or neutrophils were transformed in vitro after infection with T. parva. After transformation, peripheral blood T cells and T-cell clones retained expression of most or all of the T-cell differentiation antigens including the mature T-cell marker recognized by monoclonal antibody IL-A27, BoT2, and BoT4 or BoT8, and some cells acquired a low level of expression of BoT4, BoT8, or the null cell marker recognized by monoclonal antibody IL-A29. T. parva-transformed null cells retained expression of the IL-A29 determinant and acquired expression of BoT2 and BoT8 but not the IL-A27 determinant or BoT4. T. parva-transformed B cells in most instances lost expression of surface immunoglobulin and never acquired expression of the IL-A27 determinant, BoT2, BoT4, or BoT8, although some cells acquired a low level of expression of the null cell marker recognized by monoclonal antibody IL-A29. Further studies on cell lines and clones grown in vitro from populations isolated from T. parva-infected cattle suggested that the majority of the in vivo T. parva-transformed cells were of T-cell origin.

Bovine helper T-cell clones specific for lymphocytes infected with Theileria parva (Muguga)

T-cell clones specific for lymphocytes infected with Theileria parva were derived from animals immunized by infection with T. parva (Muguga). These clones were non-cytolytic and had the BoT4+ BoT8- surface phenotype, BoT4 and BoT8 being the bovine analogues of human CD4 and CD8 molecules. The clones proliferated in response to irradiated autologous lymphoblasts infected with T. parva (Muguga) but not to autologous uninfected lymphoblasts or monocytes. They were parasite strain-specific, in that they did not respond to autologous lymphoblasts infected with another parasite stock, T. parva (Marikebuni). The clones proliferated in the absence of exogenous T-cell growth factor (TCGF) and produced TCGF when stimulated with concanavalin A. Induction of proliferation of the cloned T-cells was genetically restricted, and evidence was obtained which indicated that they were restricted by determinants on class II major histocompatibility complex (MHC) molecules. These findings demonstrate that infections with T. parva stimulate antigen-specific MHC-restricted T-cells with the properties of T-helper cells. The results also provide further evidence for the expression of a parasite strain-specific antigen on the surface of T. parva-infected lymphocytes.

Isolation of Theileria parasites from African buffalo (Syncerus caffer) and characterization with anti-schizont monoclonal antibodies

Antigenic differences between intra-lymphocytic theilerial parasites isolated from the blood of 18 African buffalo and grown in vitro were assessed with anti-schizont monoclonal antibodies (mAbs). There was marked antigenic diversity both between isolates from different buffalo and between isolates taken at different times from the same buffalo. Many of the isolates from both wild and captive buffalo appeared to consist of mixed parasite populations. Some isolates were found by limiting dilution cloning and mAb testing to contain at least 3 or 4 distinct populations of Theileria. Once cloned, Theileria-infected lymphoblastoid cell lines retained their mAb profiles during prolonged in vitro cultivation and, when recloned, the subclones had the same mAb profile as their parent clone. The implications of these results for further studies on buffalo-derived theilerial parasites are discussed.

Characterization of species and strains of Theileria

A variety of methods is now available for characterizing species and strains of Theileria. For many practical purposes involving field control of theileriosis, characterization on a broad basis may be sufficient, but in other areas much more precise characterization is required. Such precision can be usefully exploited only when cloned parasite populations are involved, and methods to improve parasite characterization and parasite cloning should be developed concurrently. The current methods of immunization against theileriosis involve the use of live parasite populations which are generally poorly defined and, in addition, have the capacity to undergo biological change (by selection, mutation or genetic recombination) within hosts and vectors. Such changes may be difficult to define and identify, but could have profound effects on immunization strategies. Improved methods of parasite characterization and selection, which are now becoming available, will enable parasite stocks for immunization to be identified and selected more precisely, and any biological changes that occur can be monitored. Improved methods of parasite characterization will also open the way to a better understanding of Theileria genetics and the mechanisms of heritability, which appear to differ in some fundamental ways from patterns of Mendelian inheritance. Controlled matings between selected and defined populations of parasites can be envisaged, with the aim of producing hybrid parasites for immunization. In addition, the prospects of modifying the theilerial genome by genetic manipulation become very real: transfection vectors tailored by restriction enzymes could be used to insert or modify gene sequences to develop parasites with appropriate sets of characters. It may also be possible to identify parasite genes which trigger the cytotoxic response which is so important in immunity (Eugui and Emery, 1981; Emery et al., 1981; Preston et al., 1983). Such genes might then be transfected into bovine host lymphocytes to generate immunity against the whole parasite (Iams, 1985). The gene products which are responsible for stimulating immune responses could also be synthesized artificially and used for vaccination. Methods of characterizing Theileria range from Giemsa's staining to DNA hybridization; all have a role to play, and by judicious selection of appropriate methods for particular circumstances, it is becoming possible to characterize theilerial parasites very precisely. Improved methods of characterization can, in turn, lead to a better understanding of parasite biology and to the development of improved methods of immunization and control.

Comparative analysis of infection and transformation of lymphocytes from African buffalo and Boran cattle with Theileria parva subsp. parva and T. parva subsp. lawrencei

This study compared infection and transformation of peripheral blood mononuclear cells (PBM) of Boran cattle and African buffalo in vitro to determine whether differences occurred which could account for the greater susceptibility of Boran cattle to infection with Theileria parva subsp. parva and T. parva subsp. lawrencei. PBM from buffalo and cattle had a similar percentage of cells which bound T. parva subsp. parva sporozoites (24 to 34%) and in which schizonts developed during the first week after infection (18 to 23%). Using a limiting dilution culture system, it was established, however, that a significantly higher proportion of cattle PBM transformed into continuously replicating cell lines after infection with T. parva subsp. parva than did buffalo PBM. The evidence suggests that the low capacity of T. parva subsp. parva to establish infections in buffalo compared with cattle is related to the lower frequency of buffalo cells which undergo transformation. With T. parva subsp. lawrencei, however, the frequency of transformation of buffalo PBM was higher than that for cattle PBM. The frequency of cells transformed by T. parva subsp. lawrencei, therefore, cannot account for the greater resistance of buffalo to infections with T. parva subsp. lawrencei. Buffalo must have other mechanisms, either innate or acquired, which control infection with T. parva subsp. lawrencei more efficiently than in cattle.