A Dermatopathologist's Guide to Troubleshooting Immunohistochemistry Part 1

Immunohistochemistry (IHC) is a method by which specific target antigens can be detected in formalin-fixed paraffin-embedded tissue and involves the use of monoclonal or polyclonal antibodies; visualization of specific tissue antigens is achieved through an enzymatic reaction that transforms a colorless chromogen to a colored one. These enzymes may be attached to the antibody through a protein–ligand method (eg, biotin–avidin or biotin–streptavidin) or through a secondary antibody. Epitopes that are masked by protein linkage during formalin fixation are unmasked using a retrieval system that either uses heat (heat-induced epitope retrieval) or proteolytic enzymes (proteolytic-induced epitope retrieval). Part 1 of this review will focus and elaborate on the available methodologies for IHC testing, common problems inherent to each technique, and how they can be resolved. Part 2 will focus on common problems and artifacts encountered during IHC staining, likely causes, and methods for addressing each problem.