Application of heat-induced antigen retrieval to aldehyde-fixed fresh frozen sections

We applied the heat-induced antigen retrieval (HIAR) to alclehyde-fixed fresh frozen sections based on a new approach (i.e., a rapid and complete immobilization of antigen followed by heating). Frozen sections were fixed with 10% formalin in 0.1 M cacodylate buffer (pH 7.4) containing 25 mM CaCl2 for 30 min, or with 0.5% glutaralclehyde in 0.1 M phosphate buffer (pH 7.4) for 1 min at room temperature, and then autoclaved in 20 mM Tris-HCl buffer (pH 9.0) for 10 min at 120C. Both fixatives yielded good tissue structure after autoclaving. In the sections fixed with formalin containing CaCl2, 20 of 22 antigens located in the nucleus, cytoplasm, membranes, and extracellular matrix greatly recovered their antigenicity after autoclaving; only two antigens exhibited stronger immunoreaction in acetone-fixed fresh frozen sections than these sections. Heating also retrieved the immuncireactivity of at least 14 antigens in the sections fixed with glutaralclehyde. We used the similar procedures to localize ligand-free estrogen receptor alpha (ER alpha) and glucocorticoid receptors (GR). Mouse uterine cells exhibited almost the same nuclear ER alpha immunostaining regardless of the hormonal status in glutaraldehyde-fixed fresh frozen sections and unliganded GR was localized mainly in the nucleus of mouse hepatocytes in fresh frozen sections fixed with 20% formalin containing 50 or 75 mM CaCl2 at 40C, after autoclaving. These results demonstrate that HIAR is useful for the immunohistochemistry of many antigens in alclehyde-fixed fresh frozen sections.