Effect of tissue fixatives on the immunohistochemical expression of ABH blood group isoantigens

Immunohistochemical analysis of ABH blood group isoantigens has been shown to be a useful ancillary technique for resolving problems associated with specimen mix-ups in the daily practice of surgical pathology. However, the effects of different fixatives on the expression of these antigens in paraffin-embedded tissues are not known. Therefore, the effects of seven different fixatives on the immunohistochemical expression of ABH blood group isoantigens were studied in tissues from several organs. The following fixatives were used: acetone, 70% ethanol, B5, Bouin, Carnoy, methanol, and 10% formalin. After fixation for 6, 12, and 72 hours, the tissue blocks were embedded in paraffin, and immunohistochemistry was performed on 4-mum-thick tissue sections using monoclonal antibodies to blood group isoantigens (A, B, and H) and the avidin-biotin detection method. Also, immunostaining was performed on step tissue sections with and without antigen retrieval using citrate buffer at pH 6.0. The expression of the blood group isoantigens was concordant with the blood group of the patient in all the cases studied, irrespective of the fixative and time of fixation. However, in the absence of antigen retrieval, the intensity of the staining reaction was diminished. These results showed that irrespective of the fixative used, immunohistochemical staining of paraffin-embedded tissue sections with ABH blood group antibodies is a rapid, reliable, and cost-effective method for sorting out interpretative problems of tissue contaminants (floaters) and specimen mix-ups in surgical pathology.