The activity of macrophage aggregates in the liver of flounder ( Platichthys flesus) and wrasse ( Symphodus melops) is associated with tissue damage

Abstract

The phagocytic activity of macrophage aggregates (MAs) in the liver of fish is characterized by high acid phosphatase activity and generation of reactive oxygen species (ROS). Question of the present study was whether these activities were associated with damage of adjacent and surrounding liver cells and the macrophages itself. Thus, the lysosomal membrane stabilities (LMS) of two different populations of lysosomes (LMS1, short destabilization periods, and LMS2, longer destabilization periods) of liver cells close to MAs of different phagocytic activity were measured as indicator for cellular integrity by computer assisted image analysis. They were then compared to the LMS of hepatocytes remote from any MA. In addition, LMS was also assessed inside the MAs. Studies were performed on adult European flounder ( Platichthys flesus) and corkwing wrasse ( Symphodus melops) caught at clean and polyaromatic hydrocarbon (PAH)-contaminated field locations of the German Bight and the Karmoy peninsula at the West coast of Norway. In the hepatocytes adjacent to MAs which showed medium to high phagocytic activity, LMS was significantly decreased with a reduction of both, first (LMS1), and second (LMS2) destabilization periods in both species. LMS1 inside of these MAs was extremely low, whereas LMS2 was sometimes even higher compared to the liver cells. We suggest that LMS1 represents phagosomes which had contact to ROS and LMS2 represents less affected primary lysosomes. In single flounder and wrasse with liver tumors, MAs in the vicinity of these tumors showed low phagocytic activity and were not associated with adverse effects on adjacent tumor cells. Inside these MAs, LMS1 was higher compared to MAs with high phagocytic activity in wrasse from the reference site, indicating that cytotoxicity was not involved in their phagocytic deficiency.