Proteolytic-induced epitope retrieval (PIER), also known as enzyme retrieval, was the first method developed to reduce the antigen-masking effects of formalin fixation. With PIER, proteolytic enzymes break apart the protein cross-linkages formed by formalin fixation. Proteolytic enzymes used in PIER include Proteinase K, Pepsin, and Trypsin.
When using proteolytic-induced epitope retrieval methods, caution must be given to temperature and time. Each enzyme activates at a specific temperature, and variances in time and/or temperature can cause extensive damage to the tissue section quickly. This could result in loss of staining signal or complete section loss.
PIER can be detrimental to the visualization of some antibodies, sometimes producing false-positive or false-negative results. Additionally, PIER is favored when demonstrating immunoglobulins and complement in formalin-fixed, paraffin-embedded (FFPE) samples.
