Lymphoid physiology of the sheep

Abstract

The aim of this thesis is to bring together and summarize the results of twenty-five years of active research into the immunology and physiology of the mammalian lymphoid system using the sheep as the model species. For this work I have exploited the cannulation of peripheral lymphatics, which enables the monitoring of lymph, lymphocytes and dendritic cells that are constantly trafficking from the skin or from lymph nodes. The use of this technique in the sheep permits access to large numbers of lymph-borne cells over extensive periods and in a form far closer to their in vivo non-activated state than from any other species. I have organized the publications into four distinct, but interrelated chapters. Chapter 1 is concerned with the physiology of sheep lymphoid cells and describes the use of the cannulated lymphatic model to answer fundamental questions of lymphoid biology. My earliest work was focused on the non-random migration of lymphocytes and the identification of two lymphocyte populations; one associated with the gastrointestinal tract and other mucosal organs and the other with peripheral lymph nodes and the spleen. Later work identified two separate populations of B cells with distinct recirculation properties and also concentrated on the lymph node response to antigen and the role played by antigen in modulating lymphocyte recirculation. Much of my work in the last few years has been concerned with the biology of dendritic cells (DCs), the cell population uniquely able to induce the primary immune response. The "pseudo-afferent" cannulation system in sheep is, arguably the best system for this study, as the isolation procedure does not lead to aberrant changes in cell phenotype and function.Chapter 2 relates the work to characterize the sheep immune system, in order to exploit further the sheep as a species for immunological study. Much of my efforts involved the production and characterization of antisheep MHC and CD1 monoclonal antibodies (mAbs). This resulted in the generation of monoclonal reagents that are now the standards used to define the ovine/bovine homologues of MHC class I, class II and CD1. The production and use of anti-ruminant mAbs from about 1985 required their worldwide standardization in order to maintain confidence in the quality of research. This standardization was accomplished by a series of international workshops; I was involved in all, and chaired the last two. This resulted in the production of standard panels of characterized mAbs that define the ruminant homologues of human differentiation antigens. Although unglamorous work, this effort was essential for the future exploitation of the sheep as an experimental animal.The third chapter is concerned with exploiting the experimental system that I have developed, to study the immunopathology of such diseases as maedi-visna virus, Trypanosoma congolense and cvansi and Theilcria annulata. The work on maedi-visna was stimulated by the fact that it is a lentivirus (like HIV) and causes much of the same pathology as HIV. However, it is not immunosuppressive, and the host-virus interactions can be investigated without the complications of opportunistic infections. The studies on the trypanosomes have produced much novel information on the ways that these two pathogens interact with the host and cause disease. The work on the role of the chancre in the infectious process also identifies possible immunological targets for anti-trypanosome prophylaxis.Finally, the fourth chapter summarizes my work on the veterinary genetics. My main interest has been ovine/bovine MHC class I and class II as well as CD1. However, a piece of serendipity led to the development of use of human mini-satellites for genetic studies in horses. This has subsequently resulted in DNA fingerprinting being used as the standard method for unambiguous identification of individual horses and for equine paternity analysis.