PERIODIC ACID AS A NONENZYMATIC ENHANCEMENT TECHNIQUE FOR THE DETECTION OF CYTOKERATIN IMMUNOREACTIVITY IN ROUTINELY PROCESSED CARCINOMAS

Aldehyde fixation results in cross-linking of proteins, thereby maskin g or destroying a number of tissue antigens. This is a well described phenomenon for cytokeratins. Although protease treatment can enhance i mmunoreactivity, many cytokeratins remain undetectable in paraffin sec tions. Recently, several authors have reported improved results with n onenzymatic microwave oven-based antigen retrieval methods for the det ection of a wide range of tissue antigens. Based on the results of the se investigations, we performed an in-depth study of cytokeratin antib ody reactivity in several carcinomas frequently observed in routine pa thology. Routinely processed tissue sections of 10 different carcinoma s pretreated with three different nonenzymatic antigen retrieval metho ds, in combination with a microwave oven step, were tested for their i mmunoreactivity with 12 different specific cytokeratin antibodies. In addition, antibodies to vimentin and S100 were tested. When compared w ith the well known and presently available nonenzymatic retrieval meth ods, the best results were observed with a periodic acid treatment. Th e periodic acid pretreatment step in combination with cytokeratin anti bodies RCK102 and RCK106 resulted in strong positive immunoreactions. These two antibodies were previously thought to be reactive with fresh frozen tissue sections only. The application of this antigen retrieva l method did not, however, yield satisfactory results with antibodies such as Lu5, AE1, and OV-TL-12/30. For these antibodies an enzyme pret reatment step is recommended. Excellent results were also observed for vimentin and S100 antibodies after pretreatment of slides with period ic acid. The periodic acid pretreatment step has great potential for e nhancing immunoreactivity of a number of antibodies when applied to ro utinely processed tissue specimens.