Bovine mixed leucocyte reactions and generation of cytotoxic cells

The inductive requirements for proliferation of bovine peripheral blood mononuclear cells (PMB) in vitro, in the allogeneic mixed leucocyte reation (MLR), the autologous MLR and the autologous Theileria MLR were compared. In order to examine the role of monocytes in these reactions, methods were developed to deplete PBM of monocytes as well as to obtain purified monocytes. Depletion of monocytes (to less than 0.2%)could be achieved reproducibly by harvesting PBM from defibrinated blood followed by incubation on plastic for 2 h. Monocytes of greater than 95% purity were obtained by sorting with a cell sorter using a monoclonal antibody specific for monocytes within PBM. It was found that monocytes were required in the stimulator population for induction of both the allogeneic and autologous MLR and that purified monocytes. Stimulator cells fixed with glutaraldehyde did not induce either an autologous or allogeneic MLR. Genetically restricted cytotoxic cells were generated in the allogeneic MLR but not in the autologous MLR. Monocytes were not required for proliferation in the autologous Theileria MLR. Furthermore, the response could be elicited using Theileria-infected cells fixed with glutaraldehyde. However, stimulation with fixed cells was dependent on the presence of monocytes in the responder population. Cytotoxic cells were generated in the autologous Theileria MLR: using PMB from immune animals, at least a proportion of the effector population generated in vitro killed in a MHC-restricted way

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 the 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 to the square root of 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

Measurements of individual alumina particle velocities and the relative slip of different-sized particles in a vertical gas - solid suspension flow using a laser - anemometer system

Particle velocities in a vertically upward gas-solid suspension flow have been measured using a laser-Doppler anemometer system. The electronic signal-processing equipment enables individual particle slip velocities to be measured, which in turn allows mixtures of different-sized particles to be successfully studied. Alumina particles in the size range 15-200 μm were used. In laminar pipe flow of fine particles (15 μm) the particle velocity profile is parabolic, but with increasing pipe Reynolds' number the profile becomes flatter. Near the pipe wall smaller particles were unexpectedly found to have greater slip than larger particles. Reasonable agreement was found between the measured centre-line slip velocities and those computed by extensive theoretical considerations. For alumina particles in excess of 30 μm diameter, Stokes' law is no longer applicable, and great care must be taken in order to obtain an accurate estimation of the slip

Cellular constituents and structural organization of the bovine thymus and lymph node

The thymus is concerned with the production of functionally mature T cells. In cattle, it consists of two lobes, each composed of multiple lobuleswith distinct cortical and medullary regions. The thymus is supported by a network of epithelial cells; in the cortex, these are delicate spindle-shaped cells which express high levels of class II MHC antigens but little or no class I antigen, whereas, in the medulla they are more pleomorphic and are rich in both class I and class II MHC antigens. The medulla also contains a population of interdigitating cells which express high levels of class II MHC antigens. The cortical lymphocytes, which make up about 85% of thymic lymphocytes; are largely negative for class I and class II MHC antigens and exhibit high affinity for the lectin, peanut agglutinin (PNA), whereas the medullary lyphocytes express detectable levels of class I MHC antigens, are negative for class II antigens and show low affinity binding of PNA. In cattle, as in other species, the structure of the lymph node is adapted to trapping and responding to foreign material which gains access to the lymphatic system. The lymph nodes possess a structural framework of reticulum cells and reticulin fibres permeated by sinuses which are also lined by reticulum cells. The solid lymphoid tissue is segregated into follicular areas, populated predominantly with B cells, and paracortical areas containing mainly T cells. Each compartment contains specialized accessory cells, namely, the follicular dendritic cells and the interdigitating cells of the papcortex. The latter, along with B cells express high levels of class II MCH antigens, whereas class I antigens are expressed on all of the cellular constituents, although they appear to be present at much lower concentrations on germinal centre lymphoblasts