[Study of the microwave fixation using the immunohistochemical method].

We evaluated microwave fixation of formalin immersed and microwave irradiated kidney and liver tissues by keratin immunostain using the paraffin embedded section. In the microwave irradiated tissues, the formalin fixed areas and the alcohol fixed areas were clearly detected because; 1) Alcohol fixed tissues are easily digested by pepsinization but formalin fixed tissues are not, and 2) Formalin fixed tissues revealed intense keratin staining after pepsinization, whereas intense keratin staining were noted in alcohol fixed tissues without preliminary pepsinization. The microwave irradiation fixed completely the tissues in about 20 sec. A thin, formalin-fixed layer was observed in the periphery of the tissues. A thin, alcohol-fixed layer was observed beneath the peripheral formalin fixed layer in some specimens. This area was thought to have been fixed during the dehydration of the paraffin blocks. However with microwave fixation, most of the central areas differed from those of the formalin or alcohol fixed areas. They showed sharp contrast on hematoxylin-eosin staining, conspicuous cellular membrane and only slight cellular shrinkage and swelling. Unlike the formalin and alcohol fixed tissues, the intensity of keratin staining was independent of preliminary pepsinization and keratin staining was observed. Therefore, the central areas were thought to be fixed by the microwave irradiation. This fixation method seems to be useful for immunostaining.