A modified reduced-temperature antigen retrieval protocol effective for use with a polyclonal antibody to cyclooxygenase-2 (PG 27)

Antigen retrieval is now a standard procedure in immunohistochemical studies of tissues for diagnosis and research. While the most commonly used protocol (20 minutes at 100°C in citrate buffer pH 6.0) is effective for many antibody/antigen combinations, experience has shown that in some instances, this standard approach fails. Under these circumstances, a successful antigen retrieval protocol may still be established by varying key conditions in the antigen retrieval process. The authors previously have advocated a test battery approach to determine the optimal conditions for antigen retrieval, illustrated here with respect to a polyclonal antibody to cyclooxygenase-2 (PG-27) that failed to give a positive staining result after orthodox antigen retrieval. The key feature of this modified antigen retrieval protocol is heating the deparaffinized tissue sections at a reduced temperature (90°C as opposed to 100°C). For this particular antibody, a boiling condition yields a negative result, a principal reason why previous investigators have used a tyramide signal amplification system to achieve satisfactory immunohistochemical results with this antibody. The optimal antigen retrieval protocol established in the authors' laboratory for this polyclonal antibody to cyclooxygenase-2 (PG-27) was evaluated in a study of formalin-fixed, paraffin-embedded cell lines and 31 bladder cancer tissue blocks using the tissue microarray technique, with side-by-side comparison between the results obtained by a tyramide signal amplification method (without antigen retrieval) and a standard immunohistochemical method with the optimized antigen retrieval protocol. The reduced temperature antigen retrieval protocol yielded a comparable or superior immunostaining for cyclooxygenase-2 both in cell lines and tissue blocks. In conclusion, use of the test battery approach allowed development of a modified antigen retrieval technique that provides a more reliable, much simpler approach for the demonstration of cyclooxygenase-2 in archival tissues.