Enzyme-induced epitope retrieval (EIER)
There are instances where proteolytic enzymes are the preferred method of tissue pretreatment. Application time and temperature conditions vary from 5-15 minutes and room temperature to 37-40° C. The following proteolytic enzymes are the most commonly used for exposing certain antigen epitopes:
- 0.1% and 0.25% trypsin, pH 7.6-7.8
- 0.25% pepsin, pH 2.0
- Proteinase K
- Protease XXIV
- Pronase
Proteolytic enzymes are available in concentrated stock to ready-to-use formats from many commercial sources. Vendors typically provide application instructions. An online Internet search can reveal formulas for the technologist wanting to prepare their own solutions.