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Biomedical subjects

W I Morrison

Publications and source records attributed to W I Morrison.

At least 37 records · Page 2Linked to original sources
PubMed1999

Differential cytokine responses of CD4+ and CD8+ T cells in response to bovine viral diarrhoea virus in cattle.

Virus-specific T cell responses were measured in cattle seropositive for bovine viral diarrhoea virus (BVDV) and compared with those from BVDV-seronegative animals. CD4+ and CD8+ T cells were purified and co-cultured in vitro with autologous, BVDV-infected monocytes over a time-course to assess the kinetics of the proliferative response. Supernatants from parallel T cell cultures were harvested and the presence of the cytokines interleukin (IL)-2, IL-4 and interferon-gamma (IFN-gamma) were measured by ELISA (IFN-gamma) or by a bioassay (IL-2 and IL-4). CD4+ and CD8+ T cells from all seropositive, but not seronegative, cattle proliferated specifically in response to BVDV-infected monocytes. Measurement of cytokines in the supernatants from proliferating T cell cultures showed that the CD4+ T cell response was type 2-like, with extremely high levels of B cell growth factor and IL-4 activity together with comparatively low levels of IL-2 activity and IFN-gamma protein. The CD8+ T cell response, although more variable, appeared to be type 1-like, with increased IL-2 and IFN-gamma but no IL-4 or B cell stimulatory activity.

Animals↗
PubMed1998

Novel vaccines against Theileria parva: prospects for sustainability.

A first-generation subunit vaccine for East Coast fever based on the Theileria parva p67 sporozoite surface antigen is entering preliminary field trials. Intensive efforts are also focused on the identification of a schizont-specific component for incorporation in a second-generation multi-component product. It is clear that many questions remain unanswered regarding the likely performance of these vaccines under field conditions. In particular, their effect on the endemic status of the parasite in targeted areas will be crucial to their sustainability. Ideally, challenge should be maintained so that immunity is boosted in the absence of repeat vaccination. In the event that efficacy of the p67 vaccine in the field reflects that observed in extensive laboratory trials, it is possible that some reduction in the heterogeneity of the indigenous parasite population will occur, and this may be accompanied by selection for more highly infective strains. In contrast, available information suggests that schizont-specific components of a second-generation subunit vaccine are unlikely to affect the endemic status of parasite populations. However, endemic stability will inevitably decline as management systems become more intensive and necessitate frequent vaccination to maintain protective cover.

Animals↗
PubMed1998

DNA typing for BoLA class I using sequence-specific primers (PCR-SSP).

The analysis of cattle MHC (BoLA) class I gene expression is an essential component of studies on immune responses and susceptibility to disease. International BoLA workshops have generated data and reagents that allow discrimination of class I molecules at the haplotype level, but progress has been limited by difficulties encountered in defining single alleles. Our aim in this study was to develop a DNA-based system for improved identification of expressed class I alleles, utilizing available cDNA sequences derived from cattle carrying a series of serologically defined class I specificities. This method has allowed more accurate typing of animals for expression of the class I genes present within a small number of haplotypes. The method has also reliably differentiated between allelic variants (identified by prior sequence analysis) and has split existing serological specificities. The data show that MHC class I genes in cattle are more polymorphic than demonstrated by serology and biochemical analysis.

Alleles↗
PubMed1998

Resistance to bovine respiratory syncytial virus (BRSV) induced in calves by a recombinant bovine herpesvirus-1 expressing the attachment glycoprotein of BRSV.

The ability of a bovine herpesvirus-1 (BHV-1) recombinant expressing the G protein of bovine respiratory syncytial virus (BRSV) to protect against BRSV infection was examined in calves. A synthetic G gene was inserted behind the gE promoter of BHV-1 to give a gE-negative, BHV-1/G recombinant. Gnotobiotic calves, vaccinated intranasally and intratracheally with BHV-1/G were challenged 6 weeks later with the Snook strain of BRSV. As controls, calves were vaccinated with a gE-negative mutant of BHV-1 which contains a frame-shift (BHV-1/gEfs). Whereas infection with BHV-1/gEfs induced only mild clinical signs, infection with BHV-1/G resulted in more severe clinical disease and higher titres of BHV-1/G were isolated from the lungs when compared with BHV-1/gEfs. Thus, expression of the G protein of BRSV increased the virulence of BHV-1 for calves. Vaccination with BHV-1/G induced BRSV-specific antibody in serum and respiratory secretions. However, only one calf developed low levels of BRSV complement-dependent neutralizing antibody. Although BHV-1/G primed calves for BRSV-specific lymphocyte proliferative responses, there was no evidence for priming of BRSV-specific cytotoxic T cells. After challenge with BRSV, there was a significant reduction in nasopharyngeal excretion of BRSV in BHV-1/G-vaccinated calves compared with controls and BRSV was isolated from the lung of only one of five vaccinated calves compared with all four control animals. In addition, the extent of gross pneumonic lesions 7 days after BRSV challenge was significantly reduced in calves vaccinated with BHV-1/G compared with controls given BHV-1/gEfs.

Animals↗
PubMed1996

Bovine gamma/delta TcR+ T lymphocytes are stimulated to proliferate by autologous Theileria annulata-infected cells in the presence of interleukin-2.

An in vitro model system has been developed in which freshly isolated resting WC1+ gamma/delta TcR+ T cells proliferate in response to cells transformed by the protozoan parasite Theileria annulata, providing a strategy in which the basis of activation of naive gamma/delta T cells can be investigated. Irradiated parasite-transformed cells stimulate the proliferation, but not cytolytic activity, of autologous peripheral blood mononuclear cells (PBMC) from non-immune animals. The proliferating cells are mainly WC1+ gamma/delta T cells. The majority of WC1+ gamma/delta T cells in freshly isolated PBMC express CD25 at a low level that increases when stimulated with T. annulata-infected cells. Purified WC1+ gamma/delta T cells fail to proliferate when cultured with irradiated T. annulata-infected cells and produce a small proliferative response to IL-2, but proliferate strongly to irradiated or lightly fixed Theileria-infected cells in combination with IL-2. The Theileria-infected cells express cytokine transcripts encoding IL-1 alpha, IL-1 beta, IL-6 and IL-10, but not IFN gamma, IL-2, IL-4 and IL-7. Purified WC1+ gamma/delta T cells stimulated with T. annulata-infected cells with or without IL-2 fail to produce IL-2 transcripts, but do produce those for TNF alpha. These experiments show that WC1+ gamma/delta T cells recognize a surface determinant on T. annulata-infected cells, that together with a second signal, which can be provided by exogenous IL-2, stimulates their proliferation.

Animals↗
PubMed1996

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.

Animals↗
PubMed1996

Influence of host and parasite genotypes on immunological control of Theileria parasites.

Infections with Theileria parva in the African buffalo are invariably asymptomatic, whereas infections in cattle usually result in clinical disease, the severity of which varies in different populations of cattle. The parasite exhibits antigenic heterogeneity, which in cattle manifests as differences between parasite strains in their cross-protective properties. A series of studies on T cell responses to T. parva in cattle have demonstrated that class I MHC-restricted cytotoxic T lymphocytes (CTL), specific for parasitized lymphoblasts, are important mediators of immunity. Cytotoxic T cell responses frequently display parasite strain-restricted specificities which appear to correlate with the capacity of strains to cross-protect. The strain specificity of CTL responses varies in animals immunized with the same parasite strain and is influenced by both host and parasite genotype. Recent studies have provided evidence that there is competition between epitopes for induction of CTL responses, which can result in a bias to strain-specific epitopes. These properties of the CTL response have important implications for vaccination. Thus, in designing a vaccine, it may be possible, by selecting parasite proteins containing appropriate CTL epitopes, to generate CTL responses that protect against a wide range of parasite strains. Although there are no comparable data on CTL responses in the buffalo, it is considered that the features of the immune response described for cattle would be advantageous for survival of parasite populations in the buffalo. Specifically, a bias in the immune responses to strain-specific determinants should favor establishment of infection in buffalo already carrying the parasite and allow fluctuation in the levels of different parasite strains during the course of persistent infection.

Animals↗
PubMed1995

Parasite strain specificity of bovine cytotoxic T cell responses to Theileria parva is determined primarily by immunodominance.

The parasite strain specificity of CTL responses to Theileria parva varies among cattle immunized with the same parasite stock. We have investigated the influence of class I MHC on the strain specificity of CTL responses to T. parva in 19 cattle of defined class I phenotype immunized with either of two T. parva populations, in which protection to subsequent reciprocal challenge correlated with CTL strain specificity. In the majority of animals the response was restricted by the products of one MHC haplotype and there was a consistent bias to some haplotypes in preference to others. In 10 of 13 cattle expressing the molecularly defined MHC specificities A10 and KN104 on one haplotype, the CTL response was restricted entirely by this haplotype, thus allowing a precise analysis of the MHC restriction specificities. The MHC restriction specificity and the parasite population used for immunization both influenced the strain specificity of the response. By examining responses in identical twins immunized with different parasites or in animals before and after challenge with heterologous parasites, animals that mounted a strain-specific response to primary infection were shown to be capable of responding to Ags shared by the two parasite populations. These findings indicate that the strain specificity of CTL responses to T. parva is not determined primarily by immune response genes that define the inherent capacity to respond, but rather is a consequence of the response in individual animals being biased toward a limited number of immunodominant peptide-MHC determinants.

Animals↗
PubMed1995

Theileriosis: progress towards vaccine development through understanding immune responses to the parasite.

Studies of the immune responses of cattle to Theileria parva have provided evidence that immunity to the parasite can operate at two levels, namely the sporozoite and the schizont-infected lymphoblast. Antibodies that neutralize the infectivity of sporozoites have been detected in the serum of hyperimmunized cattle, and a recombinant sporozoite surface antigen has been shown to induce neutralizing antibodies and protection against experimental challenge. However, the immunity that develops following primary infection with T. parva is accompanied by only low levels of antibodies to sporozoites; there is overwhelming evidence that under these circumstances protection is mediated by T cell responses against infected lymphoblasts. Potent class I MHC-restricted cytotoxic T lymphocyte (CTL) responses are detected in animals recovering from infection and treatment or challenge infections. Two recent findings have provided direct evidence for the importance of these responses in immunity. First, the strain specificity of CTL in cattle immunized with one stock of the parasite was found to correlate with the subsequent susceptibility of individual animals to challenge with a heterologous cloned parasite population (in these circumstances some animals are protected whereas others are susceptible to the heterologous challenge). Second, the adoptive transfer of lymphocytes highly enriched for CD8+ T cells, from immune to naive identical twin calves, was found to protect against experimental challenge. The CTL response in individual animals appears to be directed towards a limited number of antigenic epitopes. The antigenic specificity is determined in part by class I MHC phenotype although there is evidence that other phenomena such as antigenic competition are also involved. Current efforts are directed towards identification of the parasite antigens recognized by CTL with the eventual aim of exploring their potential for vaccination.

Animals↗
PubMed1995

At least four MHC class I genes are transcribed in the horse: phylogenetic analysis suggests an unusual evolutionary history for the MHC in this species.

Nineteen horse MHC class I specificities have been serologically identified previously at a single locus (ELA-A), and two other specificities appear to be coded at other loci. Biochemical studies indicate that there are at least two expressed loci. In order to establish the number of transcribed horse MHC class I genes, we made a cDNA library from a heterozygous animal (ELA-A3/A7), and screened for positive clones using a bovine class I probe. More than 200 class I clones were isolated in this way, and so far seven unique full length sequences have been identified. All of the sequences are predicted to code for surface expressed, functional molecules. The number of different sequences identified demonstrate that at least four genes are transcribed, although variations in transmembrane length (which is generally conserved in class I loci) suggest that five genes could be represented. Evolutionary analysis of these sequences (and two additional sequences known to represent different horse class I loci) reveals no firm relationships, such that the division between the different loci cannot be discerned. These results suggest an unusual evolutionary history for the horse MHC, the precise nature of which may be revealed only following further cross-species comparisons.

Amino Acid Sequence↗
PubMed1995

Parasite strain specificity of precursor cytotoxic T cells in individual animals correlates with cross-protection in cattle challenged with Theileria parva.

Class I major histocompatibility complex-restricted parasite-specific cytotoxic T lymphocytes (CTL) are known to be a major component of the bovine immune response to the protozoan parasite Theileria parva, but formal proof for their role in protection of cattle against infection with T. parva has been lacking. Animals immunized with one stock of T. parva show variations in the degree of protection against heterologous challenge and also in the parasite strain specificity of their CTL responses. The present study investigated the relationship of strain specificity of CTL responses and cross-protection in an effort to verify the role of CTL in protection. The parasite strain specificity of the CTL responses generated in 23 cattle immunized with either of two immunologically distinct parasite populations was examined, and the susceptibility of individual cattle to challenge with the heterologous parasite population was determined. The frequency of stock-specific or cross-reactive CTL precursor cells (CTLp) in individual animals was measured by a limiting-dilution microassay. A proportion of animals immunized with either parasite exhibited cross-reactive CTLp, whereas CTLp detected in the remaining animals were specific for the homologous parasite. On challenge with the heterologous stock, those animals with cross-reactive CTLp were solidly protected while those with strain-specific CTLp showed moderate to severe reactions, although many of them recovered. The finding of a close association between strain specificity of the CTL response and protection against challenge provides strong evidence that CTL are important in mediating immunity.

Animals↗
PubMed1994

Adoptive transfer of immunity to Theileria parva in the CD8+ fraction of responding efferent lymph.

Evidence that class I major histocompatibility complex-restricted cytotoxic T lymphocytes (CTL) are involved in immunity to malaria has highlighted the potential importance of these cells in protection against intracellular parasites. Parasite-specific CTL are a prominent feature of the immune response of cattle to Theileria parva, a related apicomplexan parasite. The relationship between the appearance of these cells in the blood of immune cattle under challenge and the clearance of infection suggests that they are involved in the control of infection, but direct evidence is lacking that CTL can mediate protection. We have made a quantitative kinetic study of CTL responses in lymph originating from infected lymph nodes in a number of immune cattle under challenge with T. parva. Direct killing activity and the frequency of CTL precursors (CTLp) within responding cell populations were evaluated. A substantial increase in the proportion of CD8+ CTL was observed between days 8 and 11 after challenge. Frequencies of CTLp as high as 1:32 were observed and activity was essentially confined to the large blasting cell fraction. The analogous response in peripheral blood was of lower magnitude and delayed by 1-2 days. The high frequency of CTLp in efferent lymph permitted the adoptive transfer of this activity between immune and naive monozygotic twin calves. In separate experiments, naive calves lethally infected with T. parva were protected by inoculation of up to 10(10) responding CD8+ T cells derived from their immune twins. Elimination of CD8+ T cells within the inoculum abrogated this effect. These findings provide direct evidence that CD8+ T cells can control T. parva infections in immune cattle.

Animals↗