Does rapid microwave fixation improve immunohistochemistry?

Microwave fixation in dilute aldehyde solution has been reported to be superior to fixation in formaldehyde for the preservation of antigens. We studied antigen preservation among tissues which were soaked in formaldehyde, dilute aldehyde, alcohol, and saline solution with or without microwave irradiation. Microwave fixation was found to be superior to conventional formaldehyde fixation with regard to antigen preservation. However, there was no detectable difference in immunostaining between any of the irradiated and nonirradiated alcohol-, aldehyde-, or even saline-treated tissues. Microwave-irradiated tissues, regardless of the fixative employed, displayed a tendency for tissue disintegration upon protease treatment, as is commonly seen in alcohol-fixed tissues. Our results suggest that the apparent improvement in antigen preservation when microwave fixation in dilute aldehyde solution is used is largely attributable to the fixation in alcohol during the graded alcohol dehydration steps in the tissue processor, rather than to any demonstrable effect of the microwave radiation per se.