Microwave-stimulated antigen retrieval - An update

Since the development of antigen labelling in the early 1940s there have been tremendous technological developments that now allow the detection of a wide range of diagnostic antigens in routinely fixed, paraffin-embedded tissue sections. Much of these developments have come about as a result of antigen retrieval. Proteolytic digestion was the most widely used method of antigen retrieval until the introduction of microwave irradiation in 1991. This marked a major milestone in immunolabelling, and has been mostly responsible for the rapid acceptance of immunohistology and its irreplaceable role in diagnosis. While other methods of generating heat were employed for retrieval, microwave irradiation has been widely employed not only for paraffin sections but also for cytological preparations, cryostat sections, plastic-ern bedded sections, for immunoelectron microscopy, in situ hybridization and for the demonstration of DNA fragmentation in apoptosis. The precise mechanism of action of microwaves remains speculative but it is evident that several factors influence its effectiveness. These include temperature and time of exposure to irradiation, pH and osmolarity of retrieval solution and the nature and duration of fixative. To achieve optimal immunolabelling, particularly of the more capricious antigens, further work is required to fully understand the influence that these factors have on immunolabelling.