Structural characterization of the melano-macrophage centres (MMC) of goldfish Carassius auratus

In the present work we have studied the organization of melano-macrophage centres (MMCs) in the peripheral lymphoid organs, including spleen, pro- and mesonephros, of the goldfish, Carassius auratus, in an attempt to clarify their cellular composition, origins and functional relationships. Histological analysis demonstrated a similar organization in the three organs on the basis of closely packed phagocytic cells containing abundant pigment. The MMCs of Carassius auratus are found throughout the parenchyma of spleen and kidney and show a close association with the vascular system, i.e. splenic ellipsoids, sinusoids of red pulp and renal blood sinuses. They exhibit distinct degree of development from small groups of actively phagocytic macrophages to large, totally or partially encapsulated centres, where effete phagocytic cells are filled by cell debris. Ultrastructural and histochemical data suggest that the main inclusion observed in the MMCs of Carassius auratus is lipofuscin. Haemosiderin occurs in lesser amounts and melanin is almost restricted to kidney MMCs,--mainly mesonephros--. Our results suggest various non-specific physiological roles for the teleost MMCs, including tissue breakdown and erythrocyte catabolism.