visualization, chromogens are processed by the enzymes horseradish peroxidase or alkaline phosphatase. In our experience, red products are easier to differentiate from melanin or other brownish pigments often found in skin biopsies. To increase sensitivity and for double staining, additional use of fluorescent probes is of value. When performing IHC, antigen retrieval methods are often needed to get satisfying results. Those methods include preheating (e.g., pressure cooker or microwave heating) in various buffers, or enzymatic predigestion with proteolytic enzymes such as trypsin or protease. If possible, recently cut slides should be used for IHC, since storage of mounted but unstained slides leads to deterioration of tissue and thus of antigens; this may lead to false-negative results.
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