A simple colorimetric method for the measurement of phagocytosis of crystals of low molecular weight compound by macrophages.

Sodium salt of 9-oxo-10-acridineacetohydroxamic acid (HCA), a new synthetic compound, forms small crystals in aqueous solutions. These crystals were easily phagocytable by the mouse bone marrow-derived macrophages. The ingested HCA crystals were visible under light microscope as dark granules. The counting of cells with the granules allowed the calculation of number of the phagocytic cells in the preparation. It was also possible to measure the amount of ingested HCA by the cells using colorimetric method. The kinetics of phagocytosis of HCA showed that the process was rapid. Quantitative measurements of ingestion of HCA reflected the phagocytic activity of the cultured cells.