Applications of immunohistochemistry

Introduction

The histological diagnosis is often clear from light microscopic examination of tinctorial-stained slides. However, in cases with varying differential diagnoses, or where molecular subtleties will add to case interpretation, immunohistochemistry may be employed to reach a conclusion. In certain circumstances, immunohistology also has a role in predicting prognosis and potential response to therapy.

It is beyond the scope of this text to provide a comprehensive list of all possible applications and the hundreds of antibodies currently available. Other excellent texts devoted entirely to that task are available (Further reading: ; ) and there are several internet-based resources (e.g. Immunohistochemistry vade mecum, Paul Bishop, see below). This appendix attempts to provide an overview of the ways in which immunohistochemistry is commonly employed in the diagnostic pathology laboratory, alongside the basic immunohistochemical panels in common usage.

The most frequent application of immunohistology is to consider the nature of neoplasms whose morphology overlaps a range of diagnostic categories. However, other applications include identification of infective agents e.g. CMV, HSV, Helicobacter. pylori , deposition of immune complexes in renal and skin disease, and typing of active cell populations, e.g. Bcl-2, Ki67.

Classification of neoplasia

A common application of immunohistochemical staining is the classification of neoplasms according to the type of cellular differentiation. Previously, histochemistry and electron microscopy were used to identify cytoplasmic features which may indicate differentiation toward a particular cell type. However, immunohistochemistry has largely superseded electron microscopy.