Differential uptake of neutral red by macrophages from three species of estuarine fish.

Macrophage endocytosis is part of the immune response to foreign material and includes the processes of phagocytosis, ingestion of particulate material, and pinocytosis, the uptake of liquid droplets. This work reports the development of a quantitative method to measure in vitro uptake of neutral red by fish macrophages, based on the spectrophotometric measurement of ingested neutral red dye. We have used this method to monitor the rates of uptake in three species of fish: spot, Leiostomus xanthurus; hogchoker, Trinectes maculatus; and summer flounder, Paralichthys dentatus. For the species tested, there appeared to be an intrinsic pattern of uptake which was highest in flounder, lowest in hogchoker and intermediate in spot. The excellent reproducibility of this assay should make it useful for detecting toxicological effects in the environment.