A study of giant cells in inflammatory lesions of the plaice (Pleuronectes Platessa.L.)

Abstract

The inflammatory process has occupied the attention of physicians since the time of the early Greeks and since then there has been a number of experimental studies on various aspects of its development. There are however still some areas of disagreement despite the importance of understanding the inflammatory process in relation to the rational interpretation of disease. Giant cells are found in certain chronic infections. They are particularly conspicuous in tuberculous lesions. They also occur in syphilitic lesions, tuberculoid leprosy and fungus infections, while inhalation of a variety of particulate materials e.g. silica (quartz), fibrous silicate (asbestos) and dust or fumes of beryllium compounds produces chronic granulomatous lesions within the lungs which also contain giant cells. Similarly, giant cells may occur in the granulomatous lesions which result when these and other particulate irritants e.g. talcum powder, gain entrance to the tissues, especially following surgical interference. Fish farming is developing rapidly, and fishes are being raised extensively for both food and sport. One of the major limiting factors on the successful expansion of intensive aquaculture systems is disease, so that the study of fish diseases is becoming a subject of considerable importance. In spite of their importance in the inflammatory process, the literature contains little information concerning giant cells in fish, probably because in the past the study of fish diseases has been largely undertaken by aetiologists and as a result is dominated by descriptions of the life cycles or biochemical properties of parasites or bacteria. The present work was carried out in an attempt to redress this balance slightly, with regard to one aspect of fish histopathology, namely the giant cells of granulomata. The intention was to determine whether production of giant cells in the inflammatory lesion of teleost fish could be provoked by irritants, such as Freund's complete and incomplete adjuvant, mycobacteria, beryllium oxide, and talcum powder. These irritants induce the classical types of giant cells (Langhans type and foreign body type) in granulomatous inflammatory lesions of homeothermic vertebrates. Throughout the study, the plaice (Pleuronectes platessa. L.) was utilized as the experimental animal because it was readily maintained in the facilities available, was readily obtainable from the White Fish Authority, Marine Fish Farm, Hunterston, Ayrshire, and there was already a considerable amount of baseline information available on its physiology and anatomy. The main histological study was carried out at 10°C but the effect of temperature variation was studied by comparing findings in fish held at 5°C. The results were supplemented by ultrastructural studies at various stages of development of the granulomatous lesion induced by Freund's complete adjuvant at 10°C. In addition to these studies, an in vitro migration inhibition test was carried out in order to demonstrate the release of migration inhibition factor (MIF), a component of the cell mediated immunity response, by lymphocytes of sensitized fish using piscine Mycobacterium as an antigen. This test confirmed that the delayed type hypersensitivity reaction is a feature of such lesions in teleost fish just as in mammals.