Phagocytic uptake of latex beads by rat peritoneal macrophages: Comparison of morphological and radiochemical assay methods

Contrary to previous reports, commercially available 1000-nm latex beads were found to be labelable with¹²⁵I, yielding a product that retained its radiolabel on storage at 4°C and when incubated in tissue-culture media. This finding permitted a radiochemical method to measure phagocytic uptake of latex particles by rat peritoneal macrophages cultured in vitro, and a direct comparison with the established method of particle counting by light microscopy. The two methods yielded closely similar data, demonstrating that the (much more convenient) radiochemical method for quantitating phagocytic uptake is both feasible and reliable. The kinetics of phagocytic uptake of the latex particles and the effect of low temperature and metabolic inhibitors (sodium fluoride and 2,4-dinitrophenol) are described. Ongoing phagocytosis did not alter the rate of fluid-phase pinocytosis by macrophages.