Nitroblue tetrazolium-dye reduction by rat peritoneal macrophages during the uptake of Diplococcus pneumoniae, type VI.

The relationship between the rate of particle ingestion and the rate of Nitroblue Tetrazolium (NBT)-dye reduction by macrophages was studied after incubation of peritoneal exudate macrophages with heat-killed type VI pneumococci. The adherence to a polyethylene surface of the macrophages during the uptake of the pneumococci was determined as well. In some experiments pneumococci opsonized with heat-stable opsonins were used as material to be ingested. The NBT-dye reduction and the surface adherence of the macrophages was enhanced when ingesting normal heat-killed pneumococci. During the uptake of opsonized, heat-killed pneumococci the macrophages showed an unaltered NBT-dye reduction and less adherence to a polyethylene surface as compared with macrophages incubated with normal heat-killed pneumococci. This implies that using opsonized pneumococci the quantitative NBT-dye reduction assay is not reliable as a parameter for macrophage phagocytosis, because the uptake was in fact enhanced. The surface adherence of the macrophages did not reflect the enhanced ingestion of opsonized bacteria either.