| Summary: | The initial aim of this project was to raise monoclonal antibodies to the haemocytes of the marine mussel, <I>Mytilus edulis, </I>which were capable of distinguishing subpopulations of haemocytes. Thirteen monoclonal antibodies were raised, including 3 antibodies for all haemocyte types, 2 specific for eosinophilic haemocytes and 8 specific for different subpopulations of basophilic haemocytes. All the antibodies were found to bind to the granules and/or cytoplasm of the respective haemocyte types. These monoclonal antibodies have illustrated some common links between phylogenetically related molluscs. A total of 11 other species were tested from 3 taxonomic orders. Cross-reactivity was most likely in those species closest taxonomically to <I>M. edulis, </I>and was also most probable with the non-selective antibodies. Functional studies have examined the effects of the monoclonal antibodies, and six others kindly provided by Dr. D. Noël (DRIM, University of Montpellier), on cell adhesion and phagocytosis. No significant differences were observed in phagocytosis, however, some indication exists of the involvement of monoclonal antibody 19E10 in cellular adhesion. The reactivity of the monoclonal antibodies with larval cells and adult tissue sections appears to be a promising technique for targeting potential haemopoietic sites. Reactivity with the antibodies was observed in undifferentiated larval cells and in adult connective tissue, the latter has previously been suggested as a haemopoietic site in bivalves. As part of the research into immune ontogeny, the immune response of the larvae of <I>M. edulis </I>has also begun to be characterized, using a disaggregation technique. To date, the enzymes arylsulphatase and phenoloxidase have been identified, and phagocytosis has been quantified in larval cells. The generation of superoxide anion has also been detected, although the levels observed were found to vary considerably with the techniques employed to manipulate the cells.
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