Monoclonal antibodies identify phenotypically and functionally distinct cell types in the bovine lymphoid system

Demonstration of two allelic forms of the bovine T cell antigen Bo5 (CD5) and studies of their inheritance

Two monoclonal antibodies (mAbs), CC17 and IL-A67, which are specific for the bovine equivalent of the CD5 antigen, Bo5, were each found to react with the cells of some animals but not others. The cattle tested were all positive for one or both of the mAbs, but the level of expression on cells expressing both determinants was slightly lower than that on cells expressing either of the determinants on their own. Both mAbs precipitated an antigen of 67 kD. However, sequential immunoprecipitation experiments with cells that reacted with both mAbs demonstrated that the determinants are present on two different sets of molecules. These findings suggested that the mAbs recognize two co-dominantly expressed allelic forms of Bo5. This was confirmed in family studies, with groups of full- and half-sibling offspring of sires and dams of defined phenotypes. These experiments also showed that the gene encoding the Bo5 antigen is not linked to the major histocompatibility complex (MHC). The frequencies of the two alleles, which have been designated Bo5.1 and Bo5.2, in the cattle populations tested were 100% and 0%, respectively, in Bos taurus, and 10% and 90%, respectively, in Bos indicus.

A study of BoLA class II antigens with BoT4+ T lymphocyte clones

It has hitherto proved difficult to phenotype cattle for class II histocompatibility antigens using standard serological techniques because of problems of reagent specificity and antigen expression on peripheral blood mononuclear cells (PBMs). We recently described the production of class II-specific alloreactive bovine T cell clones characterized by the BoT4+ phenotype. In this report we describe studies of the application of four such clones, derived from a single mixed leucocyte culture (MLC), for class II phenotyping in proliferation and cytotoxicity assay systems. Proliferation assays used irradiated PBM as stimulator cells and cytotoxicity assays used Theileria parva-infected lymphoblastoid cells as targets. Proliferation assays revealed three distinct specificities among the four clones indicating that they detected three different class II determinants. Furthermore, in a family study, the genes encoding the determinants recognized by the clones were found to be linked to the gene encoding the w10 class I A locus product on one of the w10-bearing haplotypes in our study population. Two of the clones were studied in cytolysis assays. Lack of cytolysis of one of the targets, which was derived from the PBM of an animal carrying a class II determinant detected in proliferation assay, was explained by the total lack of expression of class II antigens on the target cell line in question, as determined with 4 class II-specific monoclonal antibodies (mAb). We conclude that BoT4+ alloreactive clones provide a potentially useful and particularly discriminating way of detecting polymorphic class II antigens of cattle, especially when applied in assays of proliferative response to PBM.

A screen of mammalian antibodies on snapper (Pagrus auratus, Sparidae) peripheral blood leukocytes reveals cross reactivity of an anti-human CD3 antibody with a population of mIg(-) cells

Detailed immunological studies of the teleosts have been hampered by a lack of antibodies against cell-specific markers. Furthermore, where antibodies have been raised, in many instances they have been found to be species-specific. In comparison, many monoclonal and polyclonal antibodies exist with specificities for mammalian proteins and glycoproteins that effectively differentiate leukocyte sub-populations. In this study, we have tested a panel of 54 commercial antibodies against human and murine cell surface receptors for their ability to bind leukocytes isolated from the peripheral blood of snapper (Pagrus auratus). From this panel, one antibody, A452, which is specific for the intracytoplasmic tail of the epsilon (epsilon) chain of the T cell receptor-associated CD3 complex (CD3epsilon) bound to a subpopulation of peripheral blood leukocytes. Mutually exclusive counterstaining was observed when this antibody was used in conjunction with a monoclonal anti-snapper immunoglobulin antibody. This suggests that A452 may be binding to putative snapper T cells.

Evaluation of cell replication by bovine T cells in polyclonally activated cultures using carboxyfluorescein succinimidyl ester (CFSE) loading and flow cytometric analysis

Studies reported here demonstrated that carboxyfluorescein succinimidyl ester (CFSE) loading of lymphocytes and flow cytometric analysis is a powerful assay to assess the kinetics and extent of cellular replication by bovine T-cell subpopulations in heterogeneous cultures of peripheral blood mononuclear cells (PBMC) where subpopulation interactions can occur. As CFSE analysis allows determination of the proportion of lymphocytes that divided, as well as the number of cell divisions each cell underwent, distinctions in responses among mitogen-stimulated cultures could be made even when(3)H-thymidine incorporation was equivalent. When combined with surface staining for detection of differentiation antigens, differences among T-cell subpopulations with regard to the number of divisions their members had undergone, were found. Anti-CD3 mAb stimulated both CD8(+)and CD4(+)T cells to undergo several cell divisions in 72 hours, while there was essentially no division by gamma delta T cells. In contrast, in concanavalin A-stimulated cultures, all T-cell subpopulations had divided.

Duplicated DQ haplotypes increase the complexity of restriction element usage in cattle

The MHC of cattle encodes two distinct isotypes of class II molecules, DR and DQ. Unlike humans, cattle lack the DP locus and about half the common haplotypes express duplicated DQ genes. The number and frequency of DQA and DQB alleles means that most cattle are heterozygous. If inter- and/or intrahaplotype pairing of DQA and DQB molecules occurs, cattle carrying DQ-duplicated haplotypes may express more restriction elements than would be predicted by the number of expressed alleles. We are investigating whether duplicated haplotypes cause differences in immune response, particularly in terms of generating protective immunity. We have analyzed the Ag-presenting function of DQ molecules in two heterozygous animals, one of which carries a duplicated haplotype. We compared the class II isotype specificity of T cell clones recognizing a putative vaccinal peptide from foot-and-mouth disease virus (FMDV15). We show for the first time that bovine T cells can recognize Ag in the context of DQ molecules. We also present evidence that interhaplotype pairings of DQA and DQB molecules form functional restriction elements. Both animals showed distinct biases to usage of particular restriction elements. Mainly DQ-restricted clones were derived from the animal with duplicated DQ genes, whereas the majority of clones from the animal with a single DQ gene pair were DR restricted. Furthermore, haplotype bias was observed with both animals. These experiments show that understanding of class II chain pairing in addition to knowledge of the genotype may be important in vaccine design where effective epitope selection is essential.

Sequence and transfection of BoLA-DRB3 cDNAs

Bovine MHC (BoLA-) DRB3 alleles encoded by the DH8A, DH22A and DH24A class II haplotypes were cloned from cDNA and characterized by sequence analysis. Comparison with other full-length DRB3 sequences suggested that DRB3 alleles may have evolved through multiple lineages. All three BoLA-DRB3 alleles were shown to express on the surface of transfected cells, and the transfectants were used to define or confirm the class II specificity of a panel of monoclonal antibodies.

Immunohistology of the splenic compartments of the one humped camel (Camelus dromedarius)

The cellular composition of the different splenic compartments is well characterized in several species, but the spleen of the camel has not been studied due to the lack of specific antibodies detecting its leukocyte subsets. Therefore, 5microm frozen sections from 15 camel spleens (0.5-15 years) were studied for acid and alkaline phosphatases and for cross-reaction with antibodies specific for bovine (n=181), swine (n=14) and human (n=6) leukocyte determinants. Fifteen antibodies cross-reacted with camel spleen cells. These included 13 anti-bovine, two anti-human, but no anti-swine antibodies. The lymph follicles mainly consisted of B cells. The germinal centers showed a strong alkaline phosphatase activity. The periarterial lymphatic sheath harbored T lymphocytes. The marginal zone contained gammadelta T cells, CD45R0+, MHC class II DR+, CD44+, IL-A 24+ cells and few macrophages. The red pulp contained B, T, MHC class II DR+, IL-A24+ and gammadelta T cells and few macrophages. The periarterial macrophage sheaths contained many more macrophages than the marginal zone, so they may play a central role in the phagocytosis of the blood born particles. The alkaline phosphatase probably labeled activated B cells, but in contrast to other species no positive cells were found in the marginal zone. In general, lymphocyte compartmentalization in the camel spleen is similar to that in other species except for lower numbers of macrophages and the absence of alkaline phosphatase positive cells in the marginal zone. No age related differences were observed in the splenic compartments.

Theileria parva: sporozoite entry into bovine lymphocytes is not dependent on the parasite cytoskeleton

The main conclusion from the present study is that T. parva sporozoite entry is dependent on a functional host cell actin cytoskeleton and is not driven by the parasite. Treating lymphocytes with cytochalasin D resulted in a dose-dependent reduction in the levels of host cell infection. However, the primary effect was to block sporozoite binding and only at the highest concentration (20 microM) was sporozoite internalization significantly reduced. In fact at lower concentrations (1-10 microM) cytochalasin treatment lead to a relative increase in sporozoite internalization. The results are consistent with sporozoite entry being primarily a passive process and with a functional host cell actin cytoskeleton that is required only to maintain the molecular integrity of the surface membrane. Thus T. parva sporozoite entry differs from the process in other apicomplexans, although the results are consistent with a number of features of sporozoite biology. Treatment of lymphocytes with either the microtubule-destabilizing agent, nocodazole, or taxol, which induces microtubule polymerization, had no significant effect on sporozoite binding or entry. As both reagents had the expected effects on the lymphocyte microtubule system, it is unlikely that host cell microtubules are essential for successful sporozoite invasion or establishment.

Bovine gammadelta T-cell responses to the intracellular protozoan parasite Theileria parva

T cells bearing the gammadelta antigen receptor (gammadelta T cells) can constitute up to 50% of T cells in the peripheral blood and lymphoid organs of young cattle. We present data showing that gammadelta T cells are involved in immune responses against Theileria parva. gammadelta T cells isolated from peripheral blood mononuclear cells (PBMC) of T. parva-naive and -immune cattle proliferated in the presence of fixed or unfixed autologous T. parva-infected lymphoblasts (TpL) and heat-stressed concanavalin A (ConA)-induced blasts (ConA blasts) but not untreated ConA blasts. The specificity of response was further evaluated with a panel of gammadelta T-cell lines and clones. T-cell reactivity was blocked by GB21A, a monoclonal antibody (MAb) specific for the gammadelta T-cell receptor, but not by MAbs specific for class I and class II major histocompatibility complex (MHC) molecules. In addition, TpL but not ConA blasts from a variety of MHC-mismatched animals induced proliferation of the gammadelta T-cell lines and clones. These gammadelta T cells were found to respond to TpL infected with several different parasite stocks and failed to recognize TpL after elimination of the parasite by the theilericidal drug BW 720C. Assays for cytotoxic activity of gammadelta T cells sorted from bulk cultures of immune PBMC restimulated several times with autologous TpL demonstrated that effector cells whose specificity is similar to that of proliferating cells are generated. These results suggest that bovine gammadelta T cells are activated by and lyse T. parva-infected cells by recognizing conserved parasite-induced or parasite-derived antigens in an MHC-unrestricted fashion.

Immunization of cattle by infection with Cowdria ruminantium elicits T lymphocytes that recognize autologous, infected endothelial cells and monocytes

Peripheral blood mononuclear cells (PBMC) from immune cattle proliferate in the presence of autologous Cowdria ruminantium-infected endothelial cells and monocytes. Endothelial cells required treatment with T-cell growth factors to induce class II major histocompatibility complex expression prior to infection and use as stimulators. Proliferative responses to both infected autologous endothelial cells and monocytes were characterized by expansion of a mixture of CD4+, CD8+, and gammadelta T cells. However, gammadelta T cells dominated following several restimulations. Reverse transcription-PCR analysis of cytokine expression by C. ruminantium-specific T-cell lines and immune PBMC revealed weak interleukin-2 (IL-2), IL-4, and gamma interferon (IFN-gamma) transcripts at 3 to 24 h after stimulation. Strong expression of IFN-gamma, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and IL-2 receptor alpha-chain mRNA was detected in T-cell lines 48 h after antigen stimulation. Supernatants from these T-cell cultures contained IFN-gamma protein. Our findings suggest that in immune cattle a C. ruminantium-specific T-cell response is induced and that infected endothelial cells and monocytes may present C. ruminantium antigens to specific T lymphocytes in vivo during infection and thereby play a role in induction of protective immune responses to the pathogen.

Use of monoclonal antibodies for immunohistochemical study of bovine spleen on frozen sections

Many monoclonal antibodies reactive with bovine leukocyte differentiation antigens are now available. Immunohistochemical staining on frozen sections using these monoclonal antibodies permits study of the functional morphology of bovine spleen. This study confirms accepted notions (B and T dependent-zones) and supplies complementary data about the repartition of CD4 and CD8 cells, gamma delta T cells, MHC (Major Histocompatibility Complex) II expression, and macrophages.

Characterization of the parasite-host cell interactions involved in Theileria parva sporozoite invasion of bovine lymphocytes

Sporozoite invasion of bovine lymphocytes by Theileria parva is a pH-dependent process that occurs without the need for de novo protein synthesis. The process was inhibited by RGD(S) peptides, fibronectin and, in the presence of serum, by antibodies reactive with fibronectin. Invasion was also blocked by a range of sulphated glycoconjugates, but treatment of lymphocytes with heparitinase did not inhibit entry. Enzymic modifications of the lymphocyte surface demonstrated that trypsin-insensitive glycoproteins containing O- and N-linked carbohydrates as well as phospholipase-sensitive molecules on the host cell surface were critical to sporozoite entry. Modification of the lymphocyte surface with NEM and DTT had only marginal effects on sporozoite binding but blocked parasite internalization. Invasion was also blocked by several antibodies which cross-reacted with sporozoite surface molecules. While only a few experimental conditions specifically blocked sporozoite binding, a wider range of reagents and treatments inhibited parasite entry. The reasons for this are discussed in terms of the nature of the zippering process that facilitates sporozoite internalization.

Modulation of WC1, a lineage-specific cell surface molecule of gamma/delta T cells augments cellular proliferation

WC1, also known as T19, is the only unique gamma/delta T-cell differentiation antigen described to date other than the gamma/delta T-cell receptor. We present evidence that modulation of WC1 results in augmented proliferation of gamma/delta T cells. Immobilized IL-A29, a monoclonal antibody (mAb) specific for WC1, augmented proliferation of gamma/delta T cells in the autologous mixed leucocyte reaction (AMLR) as well as proliferation induced by either anti-CD3 or anti-CD5 mAb. In contrast, anti-CD5 mAb did not increase proliferation in the AMLR even though both CD5 and WC1 are members of the scavenger receptor cysteine-rich family of proteins and are expressed by bovine peripheral blood gamma/delta T cells. IL-A29 did not induce proliferation when assessed alone or in the presence of either phorbol myristate acetate (PMA) or interleukin-2. IL-A29 also did not induce detectable calcium mobilization when evaluated in the presence of monocytes, PMA, or following cross-linking of IL-A29 with anti-immunoglobulin antibody. We conclude that WC1 is a gamma/delta T-cell lineage-specific cell-surface differentiation antigen which is involved in activation of gamma/delta T cells using an as yet unidentified pathway.

Pathogenicity of Theileria parva is influenced by the host cell type infected by the parasite

Theileria parva has been shown to infect and transform B cells and T cells at similar frequencies in vitro. However, the majority of parasitized cells in the tissues of infected cattle are alpha/beta T cells. The aim of this study was to determine whether the cell type infected with T. parva influenced the pathogenicity of the parasite. The initial approach, which involved inoculation of cattle with autologous cloned cell lines of different phenotypes, failed to resolve the issue, because of prolonged period of culture required to clone and characterize the cell lines resulted in attenuation of the cells. As an alternative approach, cattle were inoculated with purified populations of autologous cells that had been incubated in vitro with T. parva sporozoites for 48 h. As few as 3 x 10(4) peripheral blood mononuclear cells (PBMC) treated in this way were found to produce severe clinical reactions with high levels of parasitosis. Infections of similar severity were produced with purified populations of CD2+, CD4+, and CD8+ T cells. By contrast, infected B cells gave rise to mild self-limiting infections even when administered at a 10-fold-higher dose. In animals that received infected CD4+ or CD8+ T cells, the parasitized cells in the lymph nodes on day 11 of infection were all within the CD4+ and CD8+ populations, respectively, indicating that there had been minimal transfer of the parasite between cell types. Phenotypic analyses of cultures of PBMC infected in vitro with saturating concentrations of sporozoites revealed that parasitized B cells were abundant in the cultures after 1 week but were subsequently overgrown by T cells. The results of these experiments indicate that the cell type infected by T. parva influences the pathogenicity of the parasite.

Functional expression of a cattle MHC class II DR-like antigen on mouse L cells

Cattle DRA and DRB genes, cloned by reverse-transcription polymerase chain reaction, were transfected into mouse L cells. The cattle DR-expressing L-cell transfectant generated was analyzed serologically, biochemically, and functionally. Sequence analysis of the transfected DRB gene clearly showed showed that it was DRB3 allele DRB3(*)0101 , which corresponds to the 1D-IEF-determined allele DRBF3. 1D-IEF analysis of the transfectant confirmed that the expressed DR product was DRBF3. Functional integrity of the transfected gene products was demonstrated by the ability of the transfectant cell line to present two antigens (the foot-and-mouth disease virus-derived peptide FMDV15, and ovalbumin) to antigen-specific CD4(+) T cells from both the original animal used to obtain the genes, and also from an unrelated DRBF3(+) heterozygous animal. Such transfectants will be invaluable tools, allowing us to dissect the precise contributions each locus product makes to the overall immune response in heterozygous animals, information essential for rational vaccine design.

Monoclonal antibody BLT-1, specific for the bovine homologue of CD5, reacts with the majority of mature T cells, a subpopulation of B cells and stimulates T cell proliferation

Monoclonal antibody (MAb) BLT-1, an IgG2a with kappa light chains, reacted strongly with 21% of bovine thymocytes, weakly with 15% of thymocytes, with a subpopulation of peripheral blood B cells that also expressed CD20 and with peripheral blood T cells. Practically all of the reactive thymocytes were of a large cell subpopulation. By immunoprecipitation, BLT-1 was shown to recognize a membrane molecule with a molecular mass of 67 kDa. In competitive assays for lymphocyte surface binding, BLT-1 and MAb CC-29 (which had been shown previously to react with bovine CD5) blocked one another, indicating that the epitopes recognized were identical or extensively overlapping. In contrast, another CD-5-reactive MAb, CC-17, did not block BLT-1 reactivity with lymphocytes although the reactivity of CC-17 was blocked by BLT-1, suggesting partial overlap of the epitopes or steric hindrance by BLT-1 but not by CC-17. BLT-1 was able to induce proliferation of bovine lymphocytes in culture alone if monocytes were present or in the absence of monocytes synergized with PMA. The results indicate that BLT-1 recognizes an epitope of the bovine homologue of CD5 and that perturbation of the epitope by MAb binding results in signal transduction to bovine lymphocytes.

Generation and characterization of cloned Theileria parva parasites

A 3-step procedure for cloning Theileria parva parasites was developed. The first step involved the in vitro infection of a fixed number of bovine lymphocytes with titrated sporozoites. The cell lines obtained from infections initiated using sporozoite/lymphocyte ratios below 1:100 were then selected for cloning as these contained schizont-infected cells, each of which was derived from infection with a single sporozoite. In the second step, these cell lines were cloned by limiting dilution. As sporozoites infect lymphocytes and transform to induce clonal multiplication, this step produced infected cell lines containing both cloned parasites and cloned lymphocytes. In the third step, the cloned cell lines were used to infect cattle and isolation of the parasite in ticks was made during piroplasm parasitaemia. Finally, sporozoites were harvested from infected ticks and used for further characterization. Sporozoites derived from cloned cell lines of T. parva Muguga, Marikebuni, Boleni, Uganda and buffalo-derived 7014 were characterized using monoclonal antibody profiles, DNA restriction fragment length polymorphism detected using repetitive and telomeric probes, in vivo infectivity and, in one case, cross-immunity studies. Additionally, several distinct schizont-infected lymphocyte clones were isolated from the Muguga, Mariakani and buffalo-derived 7014 stocks. The combined results of the characterization revealed that the cloning procedure selected clones of T. parva from the parental stocks which were known to contain a mixture of genetically different parasite populations. The cloning method and the clones generated will be of value in studies of the biology of the parasite and in elucidating the strain specificity of immune responses in cattle.

MHC class I molecules are an essential cell surface component involved in Theileria parva sporozoite binding to bovine lymphocytes

The major histocompatibility complex (MHC) class I molecules are ubiquitous cell surface molecules involved in the cell-mediated immune response. We show here, using a number of different, independent approaches, that these proteins are an essential component of the host cell surface receptor involved in Theileria parva sporozoite invasion. Monoclonal antibodies (mAbs) reactive with common determinants on MHC class I molecules and with beta-2 microglobulin inhibited sporozoite entry by specifically preventing the initial binding event. However, in experiments using lymphocytes from heterozygous cattle in which at least four MHC class I gene products are expressed, mAbs which reacted with only one of these products did not inhibit entry. Using a series of bovine deletion mutant cell lines from which one or both MHC class I haplotypes had been lost, sporozoite binding and entry clearly correlated with the level of class I surface expression. While the level of sporozoite entry into cells in which one of the MHC class I haplotypes was lost was only slightly lower than into the parent cells, in a double deletion cell line having less than 5% of the class I expression of the parent cells the level of infection was only 4.3% of that into the parent cells. Furthermore, sporozoite entry into cells from a spontaneously arising mutant cell line exhibiting low levels of class I expression was correspondingly low. Treatment of lymphocytes with IL-2 produced a significant increase in host cell susceptibility and sporozoite entry and this increase correlated with either an increase in the number of target molecules per host cell, or in the binding of bovine MHC class I molecules to the mAbs. In particular, a significant increase in the level of reactivity with mAb W6/32 was observed. Lastly, we show that parasite entry can be competitively inhibited with an isolated sporozoite surface protein, p67. However, p67 binds weakly to lymphocyte surface molecules and initial attempts to use p67 to isolate the relevant host cell molecule(s) have not been successful.

Proliferation and phenotype of bovine mononuclear leukocytes in cultures stimulated by pokeweed mitogen

Cell proliferation and phenotype were evaluated at 2, 4, 6, 8, 10, 12, and 14 d in cultures of bovine peripheral blood mononuclear leukocytes stimulated by pokeweed mitogen. Cell numbers in unstimulated and stimulated 2-d cultures decreased to about 45% of the number originally added. Cell numbers at 6 d in stimulated cultures increased to 96% of the number originally seeded and remained elevated from 6 to 14 d in cultures. In contrast, numbers in unstimulated cultures at 4 to 14 d decreased; < 20% of the original number remained at 14 d. The increase in cell numbers in stimulated cultures from 4 and 6 d was due primarily to an increase in CD2+ T cells, specifically the CD4+ T-cell subset. Proliferation of interleukin-2 receptor+ and major histocompatibility class II antigen+ cells increased in these cultures. Expression of these antigens decreased in unstimulated cultures. The B-cell numbers in stimulated cultures at 2 to 4 d increased and then stabilized. Concentrations of IgM in stimulated 14-d cultures were 5 to 15 times those in parallel unstimulated cultures. Overall, IgM secretion induced by pokeweed mitogen by B cells in cultures of bovine mononuclear leukocyte is associated with proliferation of CD4+ (helper-inducer) T cells, B cells, and increased expression of activation antigens.

Characterization of resting and phorbol ester or concanavalin A activated bovine lymph node cells with leukocyte specific monoclonal antibodies

Bovine lymph node cells (LNC) have been used as a model to study cell activation and proliferation. Because monoclonal antibodies to bovine lymphoid-specific surface antigens have only recently become available, these cells have not been previously characterized in regard to subpopulations. Furthermore, it was not known how expression of lymphoid differentiation antigens and subset proportionalities might change following different modes of activation of LNC. Therefore, the distribution of cell-surface differentiation antigens in unstimulated LNC as well as in LNC incubated with the mitogen concanavalin A (Con A) or the phorbol ester, phorbol dibutyrate (PDBU), was measured using a series of leukocyte-specific monoclonal antibodies and flow cytometry. Unstimulated LNC were found to have similar proportions of T cells, B cells (sIgM positive), and MHC Class II positive cells similar to bovine peripheral blood mononuclear leukocytes (reviewed by Baldwin et al., 1988a). Treatment of the LNC with PDBU or mitogenic doses of Con A induced changes in the expression of surface antigens consistent with the changes observed with human and mouse cells after similar activation. However, these two compounds did not cause identical effects. After treatment with PDBU, the percentage of cells expressing CD4 as well as the density of surface expression decreased. An increase in the percentage of cells expressing and/or density of surface expression of the pan T cell antigens CD2, CD5, CD6, MHC Class II and J5, a T cell activation antigen, also occurred. PDBU treatment also increased the percentage of CD8 positive cells. The change in CD6 following PDBU treatment has not been reported previously. Con A treatment led to a significant increase in the percentage of cells bearing CD8, CD6, MHC Class II and J5, but it had no effect on the percentages of cells positive for the other T cell markers CD5, CD4, or CD2. Because Con A is a complete mitogen and PDBU is not, the changes observed following Con A stimulation probably reflected an expansion of a particular subpopulation. In contrast, PDBU most likely modifies surface antigen expression directly. Neither treatment affected the B cell subpopulation.

Use of monoclonal antibodies for immunohistochemical study of bovine lymph nodes on frozen sections

Many monoclonal antibodies reactive with bovine leukocyte differentiation antigens are now available. Immunohistochemical staining on frozen sections using these monoclonal antibodies permits study of the functional morphology of bovine lymph nodes. Our study confirms usually accepted notions (B and T dependent-zones) and supplies complementary data about the repartition of CD4 cells (particularly intrafollicular positive cells), gamma delta T cells, MHC II expression and dendritic leukocytes.

Tick salivary gland extract and interleukin-2 stimulation enhance susceptibility of lymphocytes to infection by Theileria parva sporozoites

Intracellular parasites show host cell specificity, and precise information on the range of host cells is a prerequisite for the identification of host molecules that account for the specificity and are involved in entry processes. The sporozoite stage of the tick-borne protozoan parasite Theileria parva binds to and enters bovine lymphocytes, but precise information on the susceptibility of other cell types present at the tick attachment site is unavailable. We quantitatively examined the susceptibility of cell types known to be present at the tick attachment site by a previously established in vitro assay. Apart from lymphocytes, sporozoites also bind to and enter macrophages and afferent lymph veiled cells; they do not bind to or enter fibroblasts, granulocytes, or erythrocytes. Sporozoites are not phagocytosed by the macrophages or veiled cells but enter them as they do lymphocytes. Since the tick attachment site is a region of cellular inflammation, we also examined the effects of agents known to be present in this area on lymphocyte susceptibility. Short-term preincubation of lymphocytes with tick salivary gland extract, with compounds that induce lymphocyte proliferation, or with interleukin-2 (IL-2), a cytokine produced by activated lymphocytes, increased host cell susceptibility by between 30 and 60%. The IL-2-induced increase in host cell susceptibility could be prevented by treating the lymphocytes with the monoclonal antibody IL-A 111, which reacts with the bovine IL-2 receptor alpha chain and inhibits IL-2-driven cell proliferation. The changes induced by tick salivary gland extract and IL-2 occurred in less than 90 min. Similarly, peripheral blood mononuclear cells from an animal previously immunized with a nonrelated antigen (trypanosome variant surface glycoprotein) and stimulated in vitro with the same antigen showed increases in host cell susceptibility of between 70 and 125%. In contrast, treatment of lymphocytes with gamma interferon did not induce any increase in host cell susceptibility.

Production, immunoanalysis and selection of monoclonal antibodies for studies of polymorphism of bovine MHC class I antigens

Two monoclonal antibodies (MoAbs) were raised against bovine lymphocyte antigens of the major histocompatibility complex (MHC) for studies of the polymorphism of MHC class I antigens of African cattle. Immunoanalysis of lymphoid tissues and molecular weight data were used to characterize the epitopes seen by the MoAbs. Competitive binding assays indicated specificity of the MoAbs for two distinct epitopes. Application of the MoAbs for MHC typing of a cattle population showed that the epitopes were co-expressed on the target MHC antigen but occurred independently on non-target MHC antigens. It is concluded that, to obtain MoAbs for studies of MHC polymorphism, it is important to conduct large-scale analysis using immunoassays and population studies.

Immune CD4+ T cells specific for Theileria parva-infected lymphocytes recognize a 24-kilodalton protein

Theileria parva is a protozoan parasite that infects and transforms bovine lymphocytes. Here we report the partial purification of a T. parva-specific protein from infected lymphocytes that is recognized by CD4+ parasite-specific T-cell clones derived from immune cattle. T. parva-infected lymphocytes were homogenized in Dulbecco's phosphate-buffered saline in the presence of protease inhibitors. The antigen was purified from a postmicrosomal supernatant by using a combination of DEAE-cellulose chromatography and hydroxylapatite column chromatography. After labelling with 125I, the antigen preparation was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found to contain 8 to 10 proteins. This preparation was subjected to chromatography in phosphate-buffered saline on HPLC TSK-250/125 columns coupled in tandem. A radiolabelled protein of M(r) 24,000 correlated with antigenic activity.

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.

Babesia bovis: Bovine helper T cell lines reactive with soluble and membrane antigens of merozoites

Babesia bovis-specific T cell lines were established from cattle infected with either tick-derived or cultured parasites by stimulation of peripheral blood mononuclear cells with a crude parasite membrane fraction. Induction and enrichment of CD4+ T cells occurred over time. All cell lines responded vigorously and in a dose-dependent, MHC-restricted manner to intact merozoites, and to soluble and membrane fractions derived from merozoites by homogenization and high-speed centrifugation. Solubilization of the membrane fraction with nondenaturing zwitterionic or nonionic detergents yielded antigenic extracts which also stimulated the T cells. However, a differential response was observed, in that cell lines from one animal proliferated vigorously to the detergent extracts of the membrane fraction, whereas cell lines from a second animal proliferated only weakly to these extracts. SDS-PAGE analysis revealed common protein bands of 90 and 22 kDa in the various immunogenic fractions. Cell lines from the animal infected with cultured parasites also responded to parasite culture supernatant "exoantigens" and to the related parasite, Babesia bigemina. We conclude that antigens present in merozoite membranes and soluble parasite extracts preferentially stimulate CD4+ T cells from cattle immune to Babesia bovis. The differential pattern of response of T cell lines from different cattle suggests that more than one protein or epitope is immunodominant for T cells.

Analysis of pokeweed mitogen-induced in vitro proliferative and antibody responses of bovine lymphocytes

The functional role of subpopulations of bovine cells in the regulation of pokeweed mitogen (PWM)-induced proliferative and antibody responses of peripheral blood mononuclear cells (PBM) was analysed. Subpopulations of bovine PBM identified by specific monoclonal antibodies (mAbs) were isolated by sorting them through the fluorescence activated cells sorter (FACS). The depletion from PBM of T cells bearing the CD4 marker, recognised by mAb IL-A12, resulted in a reduction of PWM-induced responses, which could be partly reversed by the addition of CD4 positive T cells. The depletion of cells belonging to the macrophage/monocyte lineage also resulted in a reduction of PWM-induced proliferative responses. PBM depleted of CD8 positive T cells, recognised by mAb IL-A51, showed increased PWM-induced responses, which in turn were reduced by the addition of mAb IL-A51 positive cells. Proliferative and antibody responses were also obtained by PWM stimulation of FACS-purified B cells, in the presence of bovine T cell growth factor.

Induction of proliferative responses of T cells from Babesia bovis-immune cattle with a recombinant 77-kilodalton merozoite protein (Bb-1)

A major portion of a Babesia bovis-specific gene encoding a 77-kDa merozoite protein (Bb-1) produced during natural infection in cattle and in microaerophilous culture was subcloned into the pGEX1N expression vector. Recombinant Bb-1 protein fused to glutathione S-transferase (Bb-1-GST) was used to examine cellular immune responses in B. bovis-immune cattle. Sera from rabbits immunized with Bb-1-GST reacted with fusion protein and with the native antigen present in crude B. bovis but not with B. bigemina merozoites. Bb-1-GST but not GST induced strong proliferation of T lymphocytes from these immune cattle, and Bb-1-reactive T-cell lines which consisted of a mixed population of either CD4+ and CD8+ cells or CD4+, CD8+, and "null" (gamma delta T) cells were established by in vitro stimulation of peripheral blood mononuclear cells with the recombinant fusion protein. Three CD4+ CD8- and three CD4- CD8+ Bb-1-specific T-cell clones were identified after limiting-dilution cloning of the cell lines. The studies described here demonstrate that the 77-kDa protein of B. bovis contains T-cell epitopes capable of eliciting proliferation of two types of T cells in immune cattle, an important consideration for the design of a recombinant subunit vaccine.

Effects of gamma interferon, tumor necrosis factor alpha, and interleukin-2 on infection and proliferation of Theileria parva-infected bovine lymphoblasts and production of interferon by parasitized cells

Theileria parva is a protozoan parasite that infects bovine B cells and alpha beta and gamma delta T cells and transforms them into continually proliferating cells. CD4+ T. parva-antigen-specific immune T cells have been shown to produce cytokines in response to stimulation with parasitized cells, and T. parva-infected lymphocytes produce and consume T-cell growth factors and interleukin-2 (IL-2). To ascertain the role of T-cell cytokines on T. parva infections, we evaluated recombinant gamma interferon (rIFN-gamma), rIL-2, and tumor necrosis factor alpha (rTNF-alpha) for their effects on establishment, proliferation, and survival of parasitized cells. The results indicate that neither rIFN-gamma nor rTNF-alpha had an enhancing or inhibitory effect on the growth of established T. parva-infected T-cell clones, whereas bovine rIL-2 increased the proliferation of infected B-cell and alpha beta T-cell clones but not that of gamma delta T-cell clones. To evaluate the effects of the cytokines on establishment of parasitized cell lines, peripheral blood mononuclear cells were cultured in their presence immediately following infection with T. parva sporozoites. Neither rIFN-gamma nor rIL-2 altered the proportion of cells initially developing schizonts, but both enhanced establishment of infected cell lines by about twofold. In contrast, rTNF-alpha resulted in about a 33% decrease in the proportion of schizont-infected cells. Inhibitory effects on establishment of parasitized cell lines by rTNF-alpha were no longer apparent by 12 days following infection. Tests conducted during this study indicated that T. parva-infected lymphocytes also spontaneously produce IFN that is neutralized by acidic pH treatment. In conclusion, we speculate that none of these T-cell cytokines are likely to have a profound inhibitory effect in vivo on T. parva infections. Instead, IFN-gamma and IL-2 may facilitate the establishment of infection by T. parva.

Cellular interactions regulating the in vitro response of bovine lymphocytes to ovalbumin

We examined the contribution of MHC class II-restricted T cells (CD4+), MHC class I-restricted T cells (CD8+), gamma/delta T cell receptor (TCR)+ T cells, B cells and macrophages to the development and control of in vitro proliferative responses of bovine lymphocytes to ovalbumin (OA). Cell populations for in vitro assay were obtained from peripheral blood (peripheral blood leukocytes, PBL) of OA-primed cattle. Specific cell populations were depleted or purified from PBL by staining with monoclonal antibodies (MAbs) against the appropriate differentiation antigens and sorting on a Fluorescence Activated Cell Sorter (FACS). OA-specific in vitro responses of in vivo primed PBL were dependent on the presence of CD4+ T cells. Their presence could not be replaced by the inclusion of T cell growth factor (TCGF) in the culture system, indicating that CD4+ T cells probably actively proliferate in response to antigenic stimulation. Bovine CD8+ T cells and gamma/delta TCR+ T cells appeared to exert a suppressive effect on proliferative responses. No proliferation was observed in PBL after the depletion of MHC class II+ cells. In this case, the response could be restored by the addition of macrophages or LPS-activated B cells to the MHC class II- population.

Feline immunodeficiency virus infects both CD4+ and CD8+ T lymphocytes

Monoclonal populations of feline T cells, derived from a specific-pathogen-free cat and expressing either the CD4 or CD8 surface antigen, were infected in vitro with two geographically distinct isolates of feline immunodeficiency virus (FIV). Both infected T-cell subsets exhibited decreased cell viability, expressed FIV-encoded proteins, and generated reverse transcriptase activity. All clones examined retained their original surface phenotype after infection. It appears, therefore, that both CD4+ and CD8+ T cells may be productively infected by FIV in vivo.

The entry of Theileria parva sporozoites into bovine lymphocytes: evidence for MHC class I involvement

We have examined the process of Theileria parva sporozoite entry into susceptible bovine lymphocytes and have begun to identify one of the possible molecular interactions involved in the process. The entry process involves a defined series of events and we have used a number of experimental procedures in combination with a method of quantitation to examine various aspects of this process. T. parva sporozoites are nonmotile organisms and the initial sporozoite-lymphocyte interaction is a chance event which can occur at 0-2 degrees C. All subsequent stages in the process are temperature dependent, require the participation of live intact sporozoites and host cells, and involve some cytochalasin-inhibitable rearrangement of the host cell surface membrane or cytoskeleton. Sporozoite entry can be inhibited by antibodies (mAbs) reactive with major histocompatibility complex (MHC) class I molecules (IL-A 19, IL-A 88) and with beta 2 microglobulin (B1G6), whereas mAbs reactive with MHC class II molecules (IL-A 21, J 11), and a common panleucocyte surface antigen, (IL-A 87; a bovine equivalent of CD 11a) have no effect. These results indicate that MHC class I molecules play a role in the process of T. parva sporozoite entry into bovine lymphocytes although as yet the precise role has not been determined. Once internalized within the lymphocyte, a process that takes less than 3 min at 37 degrees C, the sporozoite rapidly escapes from the encapsulating host cell membrane; a process which occurs concurrently with the discharge of the contents of the sporozoite rhoptries and microspheres. The intracytoplasmic parasite is covered by a layer of sporozoite-derived fuzzy material to which host cell microtubules rapidly become associated.

Analysis of peripheral leucocyte populations in N'Dama and Boran cattle following a rechallenge infection with Trypanosoma congolense

Monoclonal antibodies, flow cytometry and routine haematological techniques were used to analyse circulating leucocyte populations in trypanotolerant (N'Dama) and trypanosusceptible (Boran) cattle following a homologous rechallenge with Trypanosoma congolense clone IL13-E3. The N'Damas developed a low, transient parasitaemia and did not develop anaemia. The Borans became parasitaemic and developed chronic anaemia but three of the five animals eventually self-cured, whilst, a group of primary-challenged Borans experienced a severe infection characterized by high levels of parasitaemia and acute anaemia. During infection the numbers of circulating B-cells increased in all three groups from day 21 onwards. The proportion of B-cells expressing the CD5 antigen increased from pre-infection levels of 5-10% of B-cells to 49-90% by day 19 post infection in all three groups. The neutrophil count declined in both Boran groups but not in the N'Damas. The CD4+ T-cell and gamma delta T-cell populations decreased in both Boran groups but did not alter significantly in the N'Damas. Although it was not possible to infer from the data, that the CD4+, gamma delta T-cell, neutrophil and erythrocyte populations were directly responsible for the differential control of the disease by the two breeds, it was possible to correlate alterations in these cell populations with the severity of the disease.

Characterisation of lymphocyte populations in African buffalo (Syncerus caffer) and waterbuck (Kobus defassa) with workshop monoclonal antibodies

In order to measure different lymphocyte populations in buffalo (Syncerus caffer) and waterbuck (Kobus defassa), we analysed the monoclonal antibodies from the 1st International Workshop on Leukocyte Antigens in Cattle, Sheep and Goats for suitable cross-reactive reagents. Peripheral blood mononuclear cells from three buffalo and three waterbuck were tested with the whole panel of monoclonal antibodies (mAbs) together with some additional antibodies against MHC and Ig. In some clusters almost all antibodies cross-reacted (CD2, CD8), in others almost none cross-reacted (CD4, CD5) and in cluster CD6, mAbs only reacted with buffalo but not waterbuck. Double staining experiments were performed on buffalo PBM with the cross-reacting antibodies, to confirm that they detected similar cell populations as in bovine PBM. This was shown with reagents against CD2, CD4, CD6, CD8, CD11, WC1, WC3 and Ig. The molecular weights of the buffalo antigens correlated well with those of the homologous cattle antigens. In the CD5 cluster, only one mAb reacted with the two wild species, and defined an unusual CD2+ CD5- cell population in buffalo. Also mAbs cross-reacting with buffalo MHC class II detected unusual expression on resting T cells. From the results presented, it is clear that the workshop panel contains mAbs against the most important T and B cell antigens of buffalo and probably waterbuck, which will allow us to compare functional lymphocyte populations in cattle and wild ruminants.

Polymorphism of the CD4 and CD5 differentiation antigens in cattle

Monoclonal antibodies (mAbs) specific for bovine CD4 and CD5 antigens have been found to identify polymorphic determinants on these molecules. In the case of CD5, mAb IL-A67 recognises one allotypic form of the antigen while four other CD5-specific mAbs in the workshop (CC17, CC29, BLT-1 and 8C11) recognise a second allotype. The CD4-specific mAbs submitted to the workshop reacted with the cells of all animals tested. However, a further two mAbs (CC26 and IL-A18) specific for CD4 were found to react with cells only from about 85% of animals tested. Sequential immuno-precipitation experiments together with family studies showed that the allotypes of CD4 and CD5 are both inherited in a simple Mendelian manner and are co-dominantly expressed. One of the CD5 allotypes was not detected in Bos taurus animals while the gene frequency of the second allotype was only about 10% in the B. indicus animals tested. The gene frequency of the CD4 allotype detected by CC26 and IL-A18 was similar in the two sub-species.

Oxytetracycline inhibition of mitochondrial protein synthesis in bovine lymphocytes infected with Theileria parva or stimulated by mitogen

Oxytetracycline (OTC) significantly inhibited cytochrome c oxidase activity in bovine lymphocytes infected with Theileria parva and in uninfected mitogen-stimulated lymphocytes. The inhibitory effect was detected in vitro within 24 h of treatment with drug concentrations as low as 1 micrograms/ml. Following mitogen stimulation of lymphocytes, concentrations of 3 and 10 micrograms/ml OTC completely inhibited an increase in cytochrome c oxidase activity for 48-72 h. This inhibitory activity was considered to be due to a direct effect on lymphoblast mitochondrial protein synthesis. As a consequence, adenosine triphosphate activity was significantly reduced in lymphocytes stimulated either by infection with T. parva sporozoites or by mitogen and then treated with OTC. The results also indicated that parasite mitochondrial protein synthesis was inhibited by OTC. The activity of OTC reported in this study could explain the suppression of disease following 'infection and treatment' immunization against East Coast fever and the in vitro drug-inhibition of schizont development.

Expression of Tac antigen component of bovine interleukin-2 receptor in different leukocyte populations infected with Theileria parva or Theileria annulata

The Tac antigen component of the bovine interleukin-2 receptor was expressed as a Cro-beta-galactosidase fusion protein in Escherichia coli and used to raise antibodies in rabbits. These antibodies were used for flow cytofluorimetric analysis to investigate the expression of Tac antigen in a variety of Theileria parva-infected cell lines and also in three Theileria annulata-infected cell lines. Cells expressing Tac antigen on their surface were found in all T. parva-infected cell lines tested whether these were of T- or B-cell origin. T cells expressing Tac antigen could be CD4- CD8-, CD4+ CD8-, CD4- CD8+, or CD4+ CD8+. Tac antigen expression was observed both in cultures which had been maintained in the laboratory for several years and in transformed cell lines which had recently been established by infection of lymphocytes in vitro with T. parva. Northern (RNA) blot analysis demonstrated Tac antigen transcripts in RNA isolated from all T. parva-infected cell lines. Three T. annulata-infected cell lines which were not of T-cell origin were also tested. Two of them expressed Tac antigen on their surface. Abundant Tac antigen mRNA was detected in these T. annulata-infected cell lines, but only trace amounts were demonstrated in the third cell line, which contained very few Tac antigen-expressing cells. In all cell lines tested, whether cloned or uncloned, a proportion of the cells did not express detectable levels of Tac antigen on their surface. This was also the case for a number of other leukocyte surface markers. In addition, we showed that the interleukin-2 receptors were biologically functional, because addition of recombinant interleukin-2 to cultures stimulated cell proliferation. Recombinant interleukin-2 treatment also resulted in increased amounts of steady-state Tac antigen mRNA. The relevance of interleukin-2 receptor expression on Theileria-infected cells is discussed.

Parasite-accessory cell interactions in theileriosis. Antigen presentation by Theileria annulata-infected macrophages and production of continuously growing antigen-presenting cell lines

Theileria annulata, a protozoan parasite of cattle, infects major histocompatibility complex (MHC) class II+ cells, particularly macrophages, and transforms them into continuously growing cell lines. We examined the effects of parasitism by T. annulata on antigen-presenting cell function. T. annulata-infected cells (TaH) presented ovalbumin (as measured by [3H]thymidine incorporation) to both resting autologous bovine T cells and ovalbumin-specific bovine CD4+ T cell lines. However, the former cells were also stimulated by TaH without exogenous antigen although to a lesser degree than in the presence of antigen. This "nonspecific" proliferation was not seen with the ovalbumin-specific T cell lines. The magnitude of response by resting T cells in the presence of antigen, to TaH or purified peripheral blood monocytes, was essentially similar. However, on a per cell basis fewer TaH were required. Considerably greater proliferation to antigen was seen with the ovalbumin-specific T cell lines in the presence of TaH compared to monocytes and again fewer TaH were required to elicit a response. The kinetics of processing did not appear to be substantially altered in TaH and the increased proliferation may be due to the elevated MHC class II expression of these cells. Genetic restriction studies with the T cell lines indicated that the restricting elements used to present ovalbumin by TaH were the same as those used by monocytes, as identified by an isoelectric focusing technique. The continuously growing cell lines provide us with a unique model for investigating parasite-accessory cell interactions in theileriosis. The augmented antigen presenting cell activity of TaH may play an important role in the pathogenesis of the disease. TaH will also provide us with a valuable resource for our antigen presentation studies. In particular, the enhanced antigen presentation by TaH enabled us to detect responses to lower levels of antigen, often an important consideration for experiments where the quantity of antigen available is the major limiting factor.

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.

Monoclonal antibody specific for bovine CD 5 antigen which enhances mitogen-induced blastogenesis and IL-2 production

This study reports on the functional characteristics of a bovine T-cell differentiation antigen recognized by the monoclonal antibody (mAb) 8C11. This mAb has previously been found to react with a 67-kD molecule shared by thymocytes and peripheral blood T cells and to be undetectable on the B cells of healthy animals. This antigen is also largely expressed on the B cells from bovine leukemia virus-infected animals. Molecules with a similar cell distribution have been described in other species (mouse, human, rat and sheep), and were termed CD5 molecules. In order to confirm the CD5-like nature of the target molecule recognized by 8C11, functional T-cell assays were carried out. We report here that this mAb, like its human and murine homologues, enhances the proliferative responses of T cells to mitogens or alloantigens but does not directly stimulate T-cell division. Moreover, we have shown an enhancing effect of this 8C11 mAb on bovine interleukin-2 production by concanavalin A-stimulated bovine peripheral blood mononuclear cells.

An evaluation of the mononuclear cells derived from bovine mammary gland dry secretions using leukocyte antigen specific monoclonal antibodies, light scattering properties and non-specific esterase staining

The distribution of mononuclear cells isolated from the bovine mammary gland during the nonlactating (dry) period was examined using monoclonal antibodies against leukocyte cell surface antigens, cellular light scattering properties, and the presence of nonspecific esterase. Most of the mononuclear cells isolated during the dry period were lymphocytes. T cells predominated until about 1 week prior to parturition. During the week prior to calving, the percentage of B cells increased until it approximated T cells. The ratio of CD4:CD8 cells was 2-3:1 for mammary gland T cells. This was similar to the ratio found in peripheral blood. At dry-off, about 12% of mammary mononuclear cells were macrophages. The macrophage percentage increased (to about 30%) at mid-dry and remained at this levels until parturition. PMN's were isolated with the mononuclear cells during the first 2 weeks dry and the week prior to calving. Three methods were used to identify mammary macrophages. Esterase staining (as an enzymatic method), forward angle/90 degrees light scatter (based on size and internal complexity), and MHC class II/forward angle light scatter (based on size and surface markers) were compared. Each method yielded similar specificity for macrophage identification. Non-adherent cell fractions, obtained by passage of the cells over Sephadex G-10 columns, were enriched in CD4 positive T cells, somewhat depleted of B cells, and depleted of macrophages and PMN's. Cells eluted from G-10 columns, with lidocaine, were mostly lymphocytes, but reflected the cells loaded onto the column.

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.

Variation in T cell responses to ovalbumin in cattle: evidence for Ir gene control

Genetic control of immune responsiveness in cattle was investigated using an antigen-dependent T cell proliferation assay in vitro. Bovine T cell proliferative responses to ovalbumin were dependent upon major histocompatibility complex (MHC) class II molecules. Responses of an unrelated panel of animals to a limiting concentration of ovalbumin after a single immunization were compared. Two discrete patterns of response were observed. One group of animals had low or non-responses which were not significantly different from the preimmune levels. Another group of animals showed significant responses. After a second immunization the majority of low responders remained low responders. There was no significant correlation between bovine MHC class I BoLA haplotype and magnitude of response within this group of unrelated animals. However, the magnitude of the T cell responses by two half-sib family groups segregated with BoLA haplotypes inherited from the sire. In contrast no significant correlation with antibody responses in vivo could be demonstrated. We suggest that the observed variation in T cell response is linked to bovine MHC class II immune response (Ir) genes.

The effects of oxytetracycline on Theileria parva in vitro

When bovine peripheral blood leucocytes were infected with Theileria parva sporozoites, immediate treatment with oxytetracycline (OTC) inhibited the development of sporozoites to mature schizonts. The extent of inhibition was dependent on drug concentration and duration of treatment. Concentrations of 5 micrograms/ml OTC, or higher, for 8 days completely inhibited the establishment of schizonts and their ability to transform host cells. A cytostatic effect on schizont-infected cell lines was found with three tetracyclines and was also demonstrated on uninfected lymphoblasts. The parasites were found to be sensitive to OTC during development to schizonts, but when mature and established within host cells, schizonts were not demonstrably affected. The infectivity of sporozoites and the binding of sporozoites to lymphocytes were not directly inhibited by OTC. The results may explain the action of tetracyclines when used prophylactically during immunization against East Coast fever, and also the reasons for the ineffectiveness of these drugs when used therapeutically during patent disease.

T lymphocyte subset alterations following bluetongue virus infection in sheep and cattle

To determine potential mechanisms of differential disease expression in ruminants infected with bluetongue virus (BTV), clinically normal, BTV-seronegative, yearling sheep and cattle were infected subcutaneously with a standardized insect-source inoculum of BTV serotype 17 (BTV-17) (three infected and one contact control each) or animal adapted BTV serotype 10 (BTV-10) (three sheep only). BTV was isolated from peripheral blood cell components of infected sheep and cattle and all infected animals showed evidence of seroconversion by 14 days post infection (PI). Sheep infected with both serotypes of BTV developed pyrexia, oral lesions, and leukopenia which were most severe on days 7-8 PI. Analysis of peripheral blood mononuclear leukocytes with specific monoclonal antibodies and flow cytometry revealed panlymphocytopenia on day 7 PI. This response was further characterized by an increase in the CD4/CD8 ratio (greater than 3) resultant from a greater decrease in absolute numbers of circulating SBU-T8(CD8+) ("cytotoxic/suppressor") lymphocytes compared to SBU-T4 (CD4)+ ("helper") lymphocytes. SBU-T19+ lymphocytes were also decreased below baseline values on days 5-14 post infection. On day 14 PI there were increased CD8+ lymphocytes and decreased CD4/CD8 ratios (approximately 0.6) in these sheep. Clinical and hematologic changes in cattle infected with BTV-17 were minimal and consisted of mild pyrexia (rectal temperature 103 degrees F) on day 9 PI in two of three infected animals and mild leukopenia on several days PI in one animal. This leukopenia was the result of a pan T lymphocytopenia with CD4/CD8 ratios in the expected range (1-2). Similar to infected sheep, infected cattle did have a shift (decrease, approximately 0.8) in the peripheral CD4/CD8 ratio associated with an increase in circulating BoT8 (CD8)+ lymphocytes on day 14 post infection. Lymphocytes in the peripheral blood of all sheep and cattle infected with BTV-17 proliferated in vitro in response to purified BTV-17. These results confirm and extend those of previous studies that indicate species differences in the hematologic response to an equivalent BTV infection in domestic ruminants.

Differential response of bovine T-cell lines to membrane and soluble antigens of Theileria parva schizont-infected cells

T-cell lines generated from Theileria parva-immune cattle were used to identify antigens associated with schizont-infected lymphoblastoid cells. Homogenates prepared from T. parva-infected cells were fractionated by differential centrifugation, and antigenically distinct soluble and membrane-bound antigens were detected by the differential stimulation of cell lines derived from two animals. Activity in the soluble fraction was not attributable to either a mitogen or interleukin 2. Activity in the membrane fraction was associated with schizont membranes as indicated by the presence in this fraction of a parasite protein detected by immunoblot analysis using a schizont-specific monoclonal antibody. Elimination of intracellular schizonts over time, using the anti-theilerial drug, parvaquone, resulted in a concomitant loss of antigenicity in infected cells and in subcellular fractions prepared from drug-treated cells, demonstrating that stimulation of Theileria-specific helper and cytotoxic T-cell responses is associated with the presence of the parasite.

Infection of bovine T cell clones with genotypically distinct Theileria parva parasites and analysis of their cell surface phenotype

Different stocks and stabilates within a stock of Theileria parva were analysed for genotypic differences and for their effect on the expression of host cell surface antigens following infection of BoT8+ T lymphocyte clones. The parasites were characterized in vitro by hybridization of T. parva-specific DNA probes to Southern blots of endonuclease-digested DNA from the infected T cell clones. Phenotypic changes in the host lymphoblastoid cells before and after infection were examined using lineage-specific monoclonal antibodies which reacted with the differentiation antigens BoT2, BoT4, Bo6, BoT8 and a null cell marker on bovine T cells. Expression of Class I and Class II major histocompatibility complex (MHC) antigens on the cell populations was also assessed. Results of this study indicate that genotypically different parasites exist among and within T. parva stabilates and that the expression of Bo6, BoT8 and the null cell marker was differentially altered by infection with parasites from different stocks or from different stabilates of the same stock. Expression of Class II antigens was significantly increased after infection. Moreover, clones that were derived from the same cell line but had genotypically distinct T. parva parasites, also showed differences in expression of Bo6 and BoT8 and the null cell marker.

Theileria parva: bovine helper T cell clones specific for both infected lymphocytes and schizont membrane antigens

Two Theileria parva-specific bovine helper T cell clones were used to identify T. parva-derived antigens expressed on the surface of schizont infected lymphoblastoid cells. Although the clones proliferated in response to both the immunizing (Muguga) and heterologous stocks of T. parva, the patterns of the responses differed, showing that the two clones recognized different antigenic epitopes. Both clones were stimulated by autologous infected cells, without an additional source of antigen-presenting cells, as well as by purified schizonts and by a subcellular membrane fraction prepared from infected lymphoblastoid cells, when antigen-presenting cells were present. The membrane fraction was shown to be enriched for schizont membranes as indicated by the presence of a schizont surface antigen detected by immunoblotting using a schizont-specific monoclonal antibody. Elimination of schizonts with the anti-theilerial drug, parvaquone, resulted in reduced antigenicity of the membrane fraction as detected by both the T cell clones and the schizont-specific monoclonal antibody. We conclude that the T. parva-infected cell surface antigens recognized by the T cell clones are of schizont membrane origin. Although the antigens have not yet been characterized biochemically, the monoclonal antibody-specific epitope appears to be distinguishable from the T cell epitopes.