The ruminant immune system

The ruminant mammals include animals that have been domesticated and allied to human civilization for at least five thousand years. Exclusively herbivorous, except for the errant billy goat, the ruminants have served mankind as a source of dairy products, meat, leather, wool and motive power. Like other mammals, ruminants possess a well-developed immune system involving antibodies, effectors and regulatory cells and a variety of non-specific accessory factors upon which much of the health of these animals depends. While sharing many immunological features and disease syndromes with other mammals, ruminants have their own highly specialized immunological features and characteristic disease problems; this justifies their consideration as a group. An example of such specialization involves the mammary gland, which has evolved an elaborate mechanism to provide neonatal animals with both nutrients and immune factors. Unlike humans, neonatal ruminants obtain no maternal antibodies in utero and therefore must depend on their provision through the mammary gland. It is this same organ which provides mankind with dairy products and which all too often becomes infected by microorganisms. Furthermore, domesticated ruminants, especially cattle and sheep, have been subjected to extensive selective breeding to ensure greater milk production, meat production or wool quality. Consequently this group includes species and races whose family lineage and performance is a matter of record. Hence, this group provides a rich source of material for geneticists and one in which an understanding of immunogenetics may have considerable economic importance. This International Symposium on the Ruminant System was organized and convened in an attempt to strengthen the basic science of immunology as it applies to this economically important group of mammals. An attempt was made to secure the participation of investigators throughout the world and from various institutional backgrounds and affiliations; there is much to be learned by juxtaposing the scientific attitudes of scientists from different lands and from research institutes with different emphasis. To achieve this objective a fourteen-member organizing committee was formed to establish the format of the meeting, topics to be covered and speakers to be invited by mutual agreement. To encourage the active participation of those investigators not invited as speakers, and especially with the goal of insuring the presentation of fresh new data by younger, less-established investigators, poster sessions open to all were also included. The format chosen for the symposium was similar to that used successfully by the Gordon Research Conferences, and in this regard the organizing committee is indebted to Dr. Alexander Cruickshank and his staff for his guidance and help in organizing the meeting. Equally as important as the presentation of scientific information, a meeting of this type often advances scientific progress merely by providing the opportunity for investigators to meet one another in an informal, congenial atmosphere. Often these contacts act catalytically to hasten the advancement of science. The site chosen and the meeting format also attempted to achieve this goal. In the interest of organization, the program of the symposium was divided into three areas: special topics, basic immunology and the immune system of the various organ systems. Included under special topics were several overviews designed to illustrate various concepts pertinent to the immune system of ruminants. Also under this heading was a session which included presentations on current methodology in ruminant immunology and the need to standardize these. A feature address by Dr. A.C. Allison completed the special topics session of the symposium. Sessions on basic immunology included ones on cellular, humoral and genetic aspects. The remaining sessions emphasized the effects of immune phenomena on selected ruminant organ-systems. Because it is somewhat artificial to divide the study of the immune system into compartments (or sessions), it is important to reflect on the interdependence of these sessions. For example, it has been long recognized that the well-being of the mother and her fetus are dependent on the digestive system for uptake of nutrients. The physiological dependence of the mammary gland on the gut has therefore long been recognized; only recently have we begun to recognize a similar immunological dependence. Although maternal antibodies are not transported to the ruminant fetus in utero, the health of the fetus nevertheless depends on the health of the mother, and not only on the health of the maternal reproductive and digestive systems but on the disease resistance of other organ-systems as well. This resistance is in no small way dependent on a protective immune system. Ruminants also suffer from many of the same diseases involving the immune system which are common to their non-ruminant counterparts, respiratory diseases, allergies, parasitic infections and enteric infections to name just a few. By far the largest number of disease causing organisms gain entrance to the host through either the respiratory or digestive tract. While non-specific physiological factors are important, experience with immunologically deficient laboratory animals and leukemic cattle unquestionably demonstrate that specific immunity is required for survival. In short, all organ-systems are interrelated in a physiological as well as an immunological sense. While such interrelationships as the gut and mammary gland are very obvious, those involving other systems may be more subtle, but they are no less important and certainly not to be ignored. While scientists in ruminant immunology should have little trouble justifying their activities from an economic standpoint, such purely practical considerations alone should not dictate our desire to understand the basic mechanisms of the ruminant immune system. On the contrary, such an approach can be extremely dangerous. In every society and discipline, pursuit of knowledge for the sake of knowledge has its rightful place. When we look at the complexities of the immune system which have emerged from studies of laboratory animals in the last 15 years, it is obvious that manipulation of this system to yield practical solutions to man's fight against disease-causing agents is not as simple as the 'Silver Bullets' envisioned by Paul Ehrlich. Hence, if we attempt to advance too quickly toward goals with economic rewards without fully understanding the basic science involved we may waste valuable time and resources and may disappoint ourselves as well as our financial supporters who thought they paid for practical solutions. If basic science can be made to flourish through governmental aid, its practical application will need little urging and can be almost trusted to the natural ways of society; the history of technology in the western world is a testimonial to that.