Enzymatic antigen retrieval is based on the proteolytic breaking of cross-links in antigenic molecules.17 (link) Thus, we tested the commonly available and in molecular laboratories frequently used enzyme Proteinase K. Following deparaffinization and hydration, Proteinase K (Qiagen, Hilden, Germany) working solution (0.6 units/mL, as described by https://www.ihcworld.com/_protocols/ epitope_retrieval/proteinase-k.htm) was pipetted onto the slides. The sections were placed into a humidity chamber (Biozol, Eching, Germany) and incubated for 15 min at 37°C; then, a cooling-off period of 10 min at room temperature followed in tris buffered saline (TBS).