Antigen localization in immunoperoxidase-stained plastic-embedded soft tissues

Immunoperoxidase stains were performed on normal and neoplastic tissue from prostate, colon, thyroid, lung, nerve, uterus, and placenta embedded in both plastic (glycolmethacrylate [GMA]) and paraffin. Positive results in plastic section were obtained for carcinoembryonic antigen (CEA), keratin, epithelial membrane antigen (EMA), thyroglobulins, S-100, prostate-specific antigen, human chorionic gonadotrophin (HCG), and beta-HCG. More delicate staining with more precise localization of antigens is noted. Superior (paraformaldehyde) fixation and cold processing followed by GMA polymerization (4 degrees C) allow for optimum antigen survival. After fixation, tissue processing involves a series of 0.1 mol/L phosphate buffer rinses with sucrose and ammonium chloride in a conventional dip-and-dunk processor placed in a 4 degrees C cold room. Acetone dehydrations are used before GMA infiltration, cold polymerization, and sectioning. Before immunoperoxidase staining, the plastic section is digested in .25% bovine trypsin for ten minutes. The immunoperoxidase methods described can be useful when small biopsies are routinely embedded in plastic to obtain improved histologic (hematoxylin-eosin) sections. There may also be research applications in quantifying antigen expression in benign, dysplastic, and neoplastic tissues by examining the stains under high power.