Application of microwave irradiation for the retrieval of masked antigenic sites to react with vimentin

ABSTRACT

To improve immunoreactivity of the tumor marker vimentin in tissues over-fixed by formalin, using microwave radiation. A total of 10 patients were studied; five cases with thyroid papillary carcinoma, 3 cases with rhabdomyosarcoma and two cases with salivary adenoma. Two serial sections of 5 micro m thickness were cut off from paraffin blocks from the previously menttioned cases. Section were placed on 10 different pairs of slides coated with an adhesive [Vecta-bond, made by Vector Laboratories] to avoid tissue removal due to microwaving steps. One of each pair of slides was incubated in 0.01 M citrate buffer [pH 6] then heated by microwave radiation, while the other slide was left untreated. Both slides were immunostained manually for vimentin using an Avidin Biotin Complex detection kit. Result: The results showed that heating improved the detection of a specific positive reaction, while weak positive and negative results were seen in the untreated slides. Heating of over-fixed slides helped in breaking cross-reacting bonds of proteins and unmasked the antigenic sites that are needed for antigen-antibody reaction. Untreated slides still had masked antigenic sites thus giving faintly stained to negative results. It is recommented to apply heat by microwave for 8-10 minutes on formalin-fixed tissues before immunostaining for vimentin to obtain optimal results: