Aspects of cellular and humoral defence mechanisms in bivalve mollusca

• Main Author: Hardy, Stephen W.
• Published: University of Aberdeen 1978
• Subjects: 594
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.458202

The main conclusions drawn in this thesis are summarised below: (1) Haemolysins. Haemolytic activity for a variety of erythrocyte types is found in M. edulis and X. edulis. These activities were heat labile, being inactivated by heating at 40°C for 30 minutes. Gel-filtration suggests that there may be more than one lytic agent in M. edulis haemolymph. This is supported by kinetic evidence and by the response to temperature of lytic activity to different erythrocyte types. This activity does not appear to be related to vertebrate complement with which it is compared. Evidence drawn from kinetic studies indicates that haemolytic activity may be due to an enzyme, possibly a phospholipase. Lysozyme-like activity and lipase activity are found in the haemolymph of M. edulis. These are not related to the haemolytic activity. (2) Haemagglutinins. Erythrocyte agglutination was found in all the bivalve species studied. The haemagglutinins of G. gigas were particularly investigated as this species lacks haemolysins. Agglutinating activity was also found for a range of particles including micro-organisms. The haemagglutinins are proteins, they are inactivated by heating at 60°C for 30 minutes, they require Ca+l"ions for activity and have a pH optimum for activity at pH7. C. gigas and M. edulis haemolymph contain separable agglutinating activities for horse and human erythrocytes. The carbohydrate binding specificity of the human agglutinin of 0. gigas is for sialic acids. This agglutinin shows high affinity for substances containing many, United, sialic acid residues. This high affinity is considered to be a result of multi-point binding. The agglutinin also agglutinates bacteria lacking sialic acids, it is suggested that the agglutinin binds to residues sterically related to sialic acids on micro-organisms. Purified human agglutinin material from C. gigas could be demonstrated to consist of homogenous subunits with a subunit molecular weight of 15,000. The total MW of the intact molecule appears to lie 5 6 between 3 x 10 and 1 x 10 from gel filtration evidence. (3) Phagocytosis. A small proportion of the haemocyte population of C. gigas will phagocytose fluorescently labelled bacteria. The numbers of bacteria phagocytosed could be enhanced by pretreating bacteria with oyster haemolymph or purified oyster agglutinin. This was a species-specific reaction as a non-oyster agglutinin of related specifity failed to enhance uptake. Agglutinin was not necessary for phagocytosis to proceed as there was considerable uptake of bacteria in the absence of opsonisation. The possible evolutionary significance of this observation is discussed.