Peroxidase-labeled Protein A, stable immunoenzyme tracer of high reactivity and comparatively low molecular weight, has been applied in immuno-electron microscopy for detection of bound IgG-type pemphigus and bullous pemphigoid antibodies. Comparing Protein A-peroxidase with peroxidase-labeled immunoglobulins, we obtained similar morphological results in corresponding incubation techniques, but lower nonspecific adsorption of Protein A-peroxidase complexes in tissues. The Protein A-peroxidase molecules showed good tissue penetration abilities. Our rapid one-step incubation procedure led to enhanced preservation of tissue fine structures, without the need of prior tissue fixation. It seems that Protein A-peroxidase is able to replace peroxidase-labeled anti-IgG for immuno-electron microscopical purposes.

Pemphigus autoantibodies, bound in the epidermis during different stages of acantholysis, were demonstrated with a new technique for immuno-electron microscopy. Peroxidase-labeled Protein A was used as a new and specific tracer for tissue-bound antibodies of the IgG-type. Advantages were: (1) A small molecular weight of the tracer, (2) a rapid tissue penetration, and (3) shortened incubation times, thus better preserved tissue fine structures. Unspecific adsorption in tissues and on cells was found to be comparatively low.