[Immunohistochemistry. What place should freeze drying of tissues be accorded?]

Immunohistochemical labeling of frozen tissue sections is a valuable technique that allows the detection of most antigens usually destroyed by fixation in conventional tissue processing. This technique, however, has a number of limitations: difficulty in storage of tissue samples, loss of morphologic details, presence of staining artifacts, diffusion of soluble proteins. The use of freeze-dried paraffin-embedded tissues is helpful in overcoming these problems: tissue morphology is better preserved than in frozen sections; a wide range of antigens can be labeled with the same staining intensity as in frozen sections; background or diffusion artifacts are uncommon; tissue blocks may be handled as conventional paraffin blocks. The technique is based on the rapid freezing of tissue samples and their subsequent freeze-drying, followed by embedding in paraffin. Because of the expense of the necessary equipment (tissue dryer) and the limited number of samples that can be processed at one time, this technique has not been widely used by routine pathological services.