Ultrastructural localization of antigenic sites on osmium-fixed tissues applying the protein A-gold technique.

The protein A-gold immunocytochemical technique has been modified to allow labeling of cellular antigenic sites on osmium-fixed or postfixed tissues. Several strong oxidizing agents have been found able to restore protein antigenicity on osmicated tissue thin sections. According to the fine structural preservation and intensities of labeling, pretreatment with sodium metaperiodate gave optimal results. Pancreatic secretory proteins (and/or proproteins) as well as insulin (and/or proinsulin) were localized over perfectly preserved rough endoplasmic reticulum (rER), Golgi apparatus, and secretory granules of the corresponding pancreatic cells; carbamyl phosphate synthetase and catalase were revealed over liver mitochondria and peroxisomes, respectively. In addition to the higher resolution in the labeling obtained using osmium-fixed tissues, the present modification confers an additional advantage to the protein A-gold technique by allowing labeling on tissues processed for routine electron microscopy.