Quantitative analysis of macrophage phagocytosis by uptake of particulate 192iridium

This study describes a method for the quantitation of macrophage phagocytosis by measuring the uptake of small particles of the radioactive inert metal, iridium (192Ir). It is shown that macrophage labeling with 192Ir was uniform, and the label was retained by the macrophages up to 21 days post-plating (when all cultures were terminated). 192Ir labeled macrophages were able to phagocytose other particles such as sheep red blood cells and were able to be activated to become tumorcidal in vitro 21 days following initial 192Ir uptake. Therefore, 192Ir could be a useful tool for the quantitative analysis and correlation of phagocytosis, tumor cytotoxicity and other macrophage functions.