A study of the Carrageenin Granuloma in the plaice (Pleuronectes Platessa.L.)

Abstract

The inflammatory response is the cornerstone of pathology, because of the frequency of its occurrence, the fundamental nature of its component reactions, and the fact that most clinical diseases can be regarded as variants of it. Although animal pathology has been studied over many years, there are still some aspects of the inflammatory process which have not been completely resolved, even for homeotherms, and the number of such aspects still undescribed in cold blooded animals, is very much greater, since there have been relatively few studies on any of the pathological responses in poikilotheFms. A small number.of workers have studied the inflammatory response in fishes, but they have almost exclusively dealt with the acute type of response [Finn and Nielson, 1971a; Roberts £t.£l. 1973a). Aquaculture is developing into an important and rapidly expanding industry in many countries of the world. Fishes are being raised for food, for sport fisheries, and as ornamental aquarium fish. It is not surprising therefore, that there has been an increase of interest in fish pathology, and it was as a contribution towards a fundamental understanding of the mechanisms of the response of teleost fish to infection that this study was undertaken. ft In mammalian pathology a great deal of information on the chronic inflammatory response has been obtained by injecting experimental animals with extracts of the marine seaweed Chondrus crispus (Carregeenln). In chronic inflammation, collagen fibre formation is a vital component of both chronic inflammation and of healing, and carrageenin, as well as being a potent irritant is a powerful stimulant to the production of collagen. In this study, carrageenin was used, by inoculation, as a stimulus to the production of chronic inflammatory lesions in the teleost fish, in order to determine whether the teleost fish was capable of producing similar responses to those occurring in response to this model irritant in the higher animals. Throughout the study, the plaice (Pleuronectes platessa.L.) was used as the experimental fish. This was because the plaice is a relatively easy fish to Keep, is readily obtainable and a considerable amount of baseline information on this marine teleost was already available from other studies (Wardle 1971; Roberts et.al. 1971; Ellis 1974), Carrageenin was injected intramuscularly into plaice, to produce a chronic granulomatous inflammatory reaction. The main study was carried out at-4he fixed temperature of 10°C., but studies were also carried out on the moderation of the carrageenin inflammatory response by reduction of temperature to 5°C., since it is well recognized that vhe rate and to some extent the quality of the inflammatory response in poikilotherms is determined by the temperature at which the response is taking place (Finn and Nielson 1971). \ After the carrageenin was injected into plaice, an active connective tissue response -eveloped as part of the chronic granuloma, experiments were therefore also carried out to investigate the specific role of L-ascorbic acid (vitamin-C) in the enhancement of collagen synthesis. Within the developed granulomata, cells resembling the plasma cell and its precursors were observed. Since this suggested the production of serum antibodies within the granulomata, specific staining for plasma cells by Unna- Pappenheim stain was carried out, and a gel diffusion precipitation test [Ouchterlony 1947) was carried out to determine the antigenicity of carrageenin. Since the granuloma contained large numbers of lymphycytes as well as macrophages, it was considered that there might well also be a delayed type of hypersensitivity (DTH) reaction taking place, in addition to the serum antibody response. Consequently a delayed type of hypersensitivity test (the migration inhibition test, NIT) was devised to measure this response. The histological observations were complemented by an electron microscope study of various stages of the developed granuloma, to determine the ultrastructure of those cells which played a significant role in this response.