The separation and characterisation of haemocytes from the mussel Mytilus edulis

The separation of haemocytes from the mussel Mytilus edulis was carried out on continuous Percoll gradients. The haemocytes separated into three distinct layers, the first comprised 97% basophilic cells, the third comprised 84% eosinophilic cells and the middle layer was a mixture of eosinophilic and basophilic cells. Enzyme cytochemistry demonstrated arylsulphatase, phenol oxidase and peroxidase associated with the haemocytes from the third layer. Lectin-binding studies showed differential binding of lectins to the separated cells. The ultrastructural morphology demonstrated that the first layer of cells was composed predominantly of small agranular cells with a high nucleus to cytoplasm ratio. The second layer comprised a mixture of cells with the majority being granular cells with small granules. The third layer was almost exclusively composed of granular cells with small and large granules. Assays to assess the function of the different cells demonstrated that respiratory burst activity, measured as the reduction of cytochrome-c, was carried out almost entirely by the eosinophilic haemocytes. Similarly, levels of phagocytosis, measured as uptake of Escherichia coli, were much higher in the eosinophilic haemocytes. Of the potential mitogenic factors investigated, concanavalin A and pokeweed mitogen showed some evidence of inducing haemocyte proliferation.