IgG molecules, Fab' fragments and IgG-peroxidase conjugates as markers in replicas of deep-etched, labeled cell...

Sheep red blood cell (SRBC) ghosts were incubated with preparations of anti-SRBC IgG, antigen-binding fragments (Fab') or IgG coupled to horseradish peroxidase (HRPO). Frozen samples of the labeled ghosts were deep-etched and replicated with platinum-carbon to visualize their surface features in the transmission electron microscope. An analysis of both size and density of surface "particles" observed on labeled ghosts was performed to evaluate which markers could be practically used to label these membranes. It was concluded that in this system a marker must exhibit a diameter of greater than 150 A (the apparent size of IgG-HRPO conjugates) to be consistently seen over extensive surface areas and to be distinguished from the background granularity of the SRBC ghost surface. This rules out the use of Fab' or IgG as markers in this system.