Influence of tissue preparation techniques on p53 expression in bronchial and bladder carcinomas, assessed by immunofluorescence staining and flow cytometry

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Abstract
In a series of bronchial and bladder carcinomas, p53 protein expression was examined. Samples from formalin‐fixed, paraffin‐embedded tissue (routine‐treated) were compared with parallel samples of fresh tissue and tissue fixed in paraformaldehyde and ethanol. The expression of p53 was measured by immunofluorescence staining and dual parameter flow cytometry, with simultaneous monitoring of DNA content. For each tumor, p53 fluorescence with different fixatives was expressed relative to fresh tissue. The p53 fluorescence signals were on average brighter from routine‐treated tissue than from fresh tissue. The tissue fixed in paraformaldehyde showed no difference from fresh tissue. In the ethanol‐fixed tissue, however, fluorescence signals were reduced by nearly 70%, and the fraction of detectable p53 positive cells in tumor tissue was reduced by more than 50%. This loss of fluorescence was probably due to a leakage of the antigen from nucleus to cytoplasm. Pepsin treatment did not influence p53 fluorescence. Within the same tumor, the Sphase fraction in p53 positive cells was significantly higher than in p53 negative cells (13.1 ± 2.0% vs. 6.5 ± 0.8%). This pattern was not influenced by formalin fixation or pepsin treatment. Our study demonstrates that in measuring a nuclear antigen, tissue handling may influence the results, and care should be taken to optimize the preparation procedure. Using the antibody PAb 1801, p53 expression measured in archival material is not reduced as compared to fresh tissue.