ALTERATION OF IMMUNOREACTIVITY BY HYDRATED AUTOCLAVING, MICROWAVE TREATMENT, AND SIMPLE HEATING OF PARAFFIN-EMBEDDED TISSUE-SECTIONS

The effects of treatment in a hydrated autoclave (121 degrees C, 2 atm for 20 min), microwave oven (in water), and simple heating (60 degree s C overnight in distilled water or 90 degrees C for 10 min in ZnSO4) on the stainability of 56 antigens by commercially available antibodie s in formalin-fixed paraffin-embedded tissue sections were evaluated. The detectability of nuclear antigens, glycoprotein, lymphocytic surfa ce markers, and chromogranin A was significantly and reproducibly impr oved by these treatments, whereas the detectability of viral antigens and peptide hormones was attenuated or unchanged. This enhancement inc ludes not only the distinctiveness of the positive staining, but also the number of positive cells, as revealed by comparing serial sections . Among these four heating procedures, microwave heating and autoclavi ng were more effective than the others on p53, c-erbB-2, and CA125, wh ereas simple heating was best for smooth-muscle actin (HHF35 and CGA7) . Generally the effects of the heating procedures for these antigens w ere consistent among the cases, but the effects on GFAP varied with th e case. The alterations we observed could significantly influence the interpretation of immunohistochemical staining of currently popular tu mor markers such as p53 in terms of their prevalence (28% vs 64% in ga stric cancer; 36% vs 82% in metastatic liver cancer) and other diagnos tically important markers.