A Dermatopathologist's Guide to Troubleshooting Immunohistochemistry--Part 2: Troubleshooting Immunohistochemical Tests in the Laboratory.

Unexpected staining patterns can arise from problems occurring in any of the steps required for IHC, some of which are discussed in part I of this CME series. Whether used to differentiate benign from malignant tumors, identify tumor subtypes, subtypes of hematopoietic malignancies, or identifying targets for therapy, the pathologist must be intimately familiar with the potential pitfalls that are inherent in the IHC methodology to troubleshoot problems in the laboratory, and more importantly, when interpreting immunohistochemical staining, to avoid pitfalls of false-positive or false-negative stains.

A Dermatopathologist's Guide to Troubleshooting Immunohistochemistry Part 1: Methods and Pitfalls.

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).