Ultrastructural studies on the cellular response of roach, Rutilus rutilus L., to the plerocercoid larva of the pseudophyllidean cestode, Ligula intestinalis

Abstract

Abstract. Infections of roach, Rutilus rutilusL., with the plerocercoid larva of Ligula intestinalis result in a pronounced host cellular response which consists of a leucocyte and connective tissue component. Using ultrastructural, histochemical and tracer techniques, three leucocyte cell types (L1, L2 and L3) have been observed. L1 cells, the most numerous cell type, pass through a number of characteristic developmental stages. Phagocytosis occurs in stages 1, 2 and 3. Stages 1 and 2 contain predominantly primary lysosomes and secondary lysosomes respectively, and in cells of stage 3 residual bodies are found which may be released following disruption of the cell at stage 4. The lysosomes and residual bodies do not contain acid phosphatase although arylsulphatase activity is present in all secondary lysosomes and residual bodies and in a few primary lysosomes. L1 cells are thought to be macrophages. L2 and L3 cells are relatively rare. The former contain granules resembling those found in mammalian eosinophils but which themselves are not eosinophilic or acid phosphatase and arylsulphatase positive. L2 cells are phagocytic and are thought to be neutrophils. L3 cells are also phagocytic and may represent macrophage precursors. Despite the presence of a host cellular response parasites survive apparently unharmed as long as the host lives. The significance of this is discussed.