The role of renal macrophages in the aglomerular kidney of the sea-horse (teleost) in the removal of exogenous macromolecules from circulating blood.

Mechanisms involved in the removal of exogenous macromolecules from circulating blood were investigated in the aglomerular nephrons of the kidney of the sea-horse, Hippocumpus kuda Bleeker, using either native anionic or cationized probes. After intraperitoneal injection of native anionic horse-spleen ferritin (HS-AF) or cationized one (HS-CF) into the sea-horse, kidneys and gills were examined morphologically at intervals of 1 h to 14 days. Histochemical and immunohistochemical studies and transmission electron microscopy of the kidneys revealed that most of the injected HS-AF or HS-CF were taken up by macrophages in the sinusoids of hemopoietic tissue through pinocytosis, being gradually accumulated into their phagolysosomes. By the 14th day, the injected ferritin particles were degraded and the ferric agglomerates were concentrated within the phagolysosomes. Then the macrophages heavily laden with densely packed ferric catabolites migrated into the hemopoietic area forming macrophage agglomerates or macrophage centers. Some HS-AF and HS-CF particles infiltrated into the tubular basement membrane, where they were taken up by the tubular epithelial cells through pinocytosis, translocated into the phagolysosomes, fragmented into small ferric catabolites and then excreted into the urinary space. In contrast, examination of the gills revealed neither HS-AF, HS-CF particles nor their histochemically detectable ferric catabolites in either the interstitial space including basal lamina or the alveolar epithelia. It seems that no appreciable egress of exogenous substances occurs from the gill into the environmental water.