Tissues that have been preserved with formaldehyde, a highly reactive compound, contain a variety of chemical modifications that can reduce the detectability of proteins in biomedical procedures such as immunohistochemistry. Antigen retrieval is an approach to reducing or eliminating these chemical modifications. The two primary methods of antigen retrieval are heat-mediated epitope retrieval (HIER) and proteolytic induced epitope retrieval (PIER).
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Antigen retrieval Wikipedia(Text) CC BY-SA