Automatic determination of labeling density in protein A-gold immunocytochemical preparations using an image analyzer. Application to peroxisomal enzymes.

The application of an automatic image analyzer (TAS, Leitz, Wetzlar) for determination of labeling density in protein A-gold labeled sections is described. Electron micrographs of rat liver labeled with 12 nm gold particles for peroxisomal enzymes are placed on the macrounit of TAS and the images of peroxisomes on TAS-monitor are contoured with a light pen. The instrument measures the surface of the contoured areas. Based on their gray level, the gold particles over the peroxisome are detected automatically and counted and the labeling density for each peroxisome is calculated.