DISTRIBUTION OF MACROPHAGES DURING FISH DEVELOPMENT - AN IMMUNOHISTOCHEMICAL STUDY IN CARP (CYPRINUS-CARPIO, L)

A monoclonal antibody against carp macrophages (WCL15) has been utilis ed in flow cytometry, immuno-histochemistry and immune-electron micros copy to assess the distribution of monocytes/macrophages in developing carp lymphoid tissues. In suspensions of living cells WCL15 reacted s trongly with cytoplasm and plasmic membrane of macrophages. It also cr oss-reacted with a subpopulation of thrombocytes, but this reaction co uld be neglected by double immunostaining in combination with a thromb ocyte-specific marker. In Bouin-fixed tissues the antibody distinctly recognised macrophages. Macrophages were found from day 2 post-fertili sation in head kidney and in the dorsal portion of the yolk sac epithe lium. From 1 week onwards macrophages were found scattered in thymus a nd gut and during the second week in spleen. Macrophages increased in number in all lymphoid tissues until the 6-8th week post-fertilisation , but they decreased except in thymus, where they became localised mai nly in the cortical-medullary boundary, and in white pulp areas of hea d kidney. The role of macrophages in allowing an early non-specific de fence in young fish and in co-operating during the differentiation pro cesses of T-cells and B-cells is discussed.