Advances in ultrastructural postembedment localization of antigens in Epon sections with peroxidase labelled antibodies.

Procedures for ultrastructural postembedment immunolocalization of antigens were investigated by use of the indirect peroxidase labelled antibody method. Results were compared with those obtained with the ultrastructural preembedment technique. IgG globulins in IgG synthesizing cells of rat lymph nodes served as model. Formaldehyde fixation, ethanol dehydration and embedment in Epon 812 did not abolish immunoreactivity. Sufficient numbers of antigens remained for subsequent postembedment immunohistology. Antigen binding sites were readily localized in ultrathin sections. For this purpose, polymerized resin had to be partially removed. Sodium methoxide in methanol/benzene mixture rapidly dissolved ultrathin sections. Diluted alcoholic sodium hydroxide enabled reliable resin etching and subsequent immunostaining. Treatment of ultrathin sections with hydrogen peroxide alone, did not permit immunolocalization of IgG. Optimal antigen detection was attained with antibodies isolated by affinity chromatography and purified peroxidase conjugates. IgG was stained in the rough-surfaced endoplasmic reticulum, the perinuclear space and the Golgi apparatus; the subcellular distribution corresponded to that obtained with preembedment immunohistology. In the latter technique, substrate accumulation was more homogenous than in postembedment staining.