Studies on the reticuloendothelial system of the dogfish Scyliorhinus canicula. Endocytic activity of fixed cells in the spleen and liver

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Abstract
The role of the spleen and liver of the lesser spotted dogfish, Scyliorhinus canicula, in the clearance of a range of materials, including colloidal carbon, latex beads, sheep red blood cells, bacteria, and dextran, was examined. The spleen was particularly important in the clearance process. Smaller particulates, such as carbon, were sequestered by the highly endocytic macrophages of the ellipsoids, while larger particles, for example, bacteria and sheep red blood cells, were mainly taken up by the fixed macrophages of the red pulp. An increase in the numbers of the eosinophilic G1 granulocytes in the red pulp of the spleen was observed following injection of the particulates. In the liver, fixed cells, probably homologous to mammalian Kupffer cells, were involved in clearance and participated in endocytosis of carbon and latex. Additionally, all of the injected particulates were internalized by cells (frequently seen to also contain melanin granules) lying within nonsinusoidal blood vessels in the hepatic parenchyma. Often, but especially in fish injected with bacteria, these phagocytic cells appeared trapped along with free bacteria, within large clumps of circulatory blood cells in the vessels. The presence of the injected materials in the spleen and liver was evident at 30 min and increased up to 1 week. The ultimate localization and differential uptake of the injected materials, and the relative importance of the spleen and liver in the clearance of these materials are discussed.