The accurate and repeatable detection of a specific protein is central to successful IHC staining. Primary antibodies bind to a small region or multiple regions (epitope/s) of these very complex proteins.
During formalin fixation the protein structure is modified by formalin cross-linkages that can mask the target epitope. Before staining formalin-fixed, paraffin-embedded (FFPE) tissue, the target site may need to be “unmasked” using a process known as epitope retrieval. There are two common methods used: Heat Induced Epitope Retrieval (HIER) and Enzyme Induced Epitope Retrieval (EIER). The choice of method depends on the primary antibody used and the retrieval method suggested by the antibody manufacturer.
Both HIER and EIER follow tissue deparaffinization and rehydration. Some automated stainers include epitope retrieval steps (both HIER and EIER). These stainers reduce the overall laboratory workload as well as providing excellent results due to their consistency and temperature control. The HIER method involves incubating the sample in a buffered solution at an elevated temperature. Successful HIER depends on buffer composition, buffer pH, heating time and temperature. The most common buffers are alkaline EDTA buffer (pH 9.0) and a mildly acidic citrate buffer (pH 6.0). There are a number of different heating methods with temperatures of 100 ºC and above providing the best results. However excessive temperature can adversely affect the epitope and tissue morphology (structure).
EIER is typically conducted at 37 ºC – 40 °C using proteolytic enzymes that digest, or physically breakdown, the cross-linking bonds. The process is faster than HIER, taking around 5 – 10 minutes. The enzyme can begin to digest and destroy the samples if incubated for too long.
A vision for high-quality IHC and ISH.
At Leica Biosystems our vison is to advance cancer diagnostics and improve lives. One way we can achieve this vision is by helping improve staining quality. As we recognize that IHC and ISH quality doesn‘t begin at the stainer, this series looks at many different aspects of staining quality, and considers how future tests will influence improved diagnosis.
This reference document is presented as a service to health care professionals by Leica Biosystems and has been compiled from available literature. Although every effort has been made to report faithfully the information, Leica cannot be held responsible for the correctness. This document is not intended to be, and should not be construed as medical advice. For any use, the product information guides, inserts and operation manuals of the various drugs and devices should be consulted. Leica Biosystems and the editors disclaim any liability arising directly or indirectly from the use of drugs, devices, techniques or procedures described in this reference document.
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