Renal portal phagocytosis of bacteria in rainbow trout (Salmo gairdneri Richardson): ultrastructural observations

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Abstract
Catheterized rainbow trout (Salmo gairdneri) were inoculated with killed bacteria and the perfused – fixed kidney was examined in the electron microscope. The endothelium of the portal circulation was continuous but had evidence of marked pinocytotic activity with large numbers of intracytoplasmic vesicles, many of which were spiny coated. Intracytoplasmic transfer tubules were also a prominent feature. Bacteria were phagocytosed by macrophages closely associated with the endothelium, but not by the endothelial cells. Macrophage pseudopodia were occasionally seen traversing endothelium to touch the underlying haemopoietic tissue. The renal portal vasculature provides a large area for efficient antigen trapping.