Salmonid macrophages: separation, in vitro culture and characterization

Abstract. A method is described for the separation of fish leucocytes and the establishment of pure monolayers of fish macrophages in vitro. The method makes it possible to study the important role of cellular immunity in fish. Fish leucocytes were obtained from the pronephros of rainbow trout, Salmo gairdneri Richardson, and compared to those obtained from the pronephros of Atlantic salmon, Salmo salar L. Single cell suspensions were separated by density gradient centrifugation and seeded on glass cover slips for maintenance in culture. After 20 h in culture a subpopulation of the cells had adhered and spread out on the cover slips and were macrophage-like by morphological criteria. About 90–99% of these cells had the ability to phagocytose a variety of particles, including fixed sheep erythrocytes, latex, carbon particles, yeast and Vibrio anguillarum. Opsonization of particles with mammalian immunoglobulins and mammalian complement did not enhance the phagocytic activity.