Abstract
Japanese conger Conger myriaster has well-developed splenic ellipsoids (sheath structure) that are thought to participate in the elimination of foreign substances and effete hemocytes from circulating blood. After injection of fluorescent latex beads (LB, 0.5 or 2.0 μm in diameter) through the aortic bulb of the Japanese conger, the spleens and kidneys were examined by light and electron microscopy. The splenic ellipsoids trapped many LB of 0.5 μm in diameter but none of 2.0 μm. This suggests that the LB were filtered by ellipsoids depending on size. Latex beads of 0.5 μm were ingested by macrophages beneath the endothelium of the arteriole in ellipsoids but not by endothelial cells. At 24 h, many 0.5 μm LB were found in the ellipsoids and splenic cord, but there were few in the melanomacrophage centers (MMC). However, most of the 0.5 μm LB had accumulated in the MMC within 48 h. Many macrophages laden with the microspheres were found around MMC. The 2.0 μm LB were detected in the splenic cord and MMC 24 h and 48 h after injection. This suggests that the macrophages take up 0.5 μm LB in the ellipsoids and migrate through the splenic cord to MMC. The process of entrapment and accumulation of particles in the kidney was also examined and discussed.
