Melano-macrophage centres and their role in fish pathology

We have studied the melano-macrophage centres (MMCs) of Carassius auratus as well as the changes they undergo in different experimental conditions. The MMCs of the spleen contain brown and yellow pigments, but dark pigments abound in those of the kidney. They occur in association with splenic ellipsoids and scattered throughout the renal parenchyma. Histochemical tests demonstrated small amounts of lipids and basic proteins, abundant neutral mucopolisaccharides and differences between the spleen MMCs and those of the kidney, specially regarding the presence or absence of haemosiderins and melanins. Electron microscopy shows them to consist of phagocytes containing degenerated debris, sometimes surrounded by a discontinuous layer of flat reticular cells. The MMCs of the spleen and kidney trap carbon material 48 hours after injection of Indian ink. Primary and -more so- secondary immunization with SRBC produces a net increase in number and size of MMCs. Treatment with phenylhydrazine produces a notable and fast increase of the MMCs in both organs. After 5 days the MMCs degenerated and erythroblasts restored the erythroid population. Apparently, MMCs represent non-specific means of phagocytosis related to different physiological processes.