Chapter 3 - Immunohistology of Infectious Diseases

Abstract

Pathologists play an important role in the diagnosis or exclusion of infectious diseases. Traditionally, the diagnosis of infectious diseases relies on serologic assays and cultures. Serologic results may be difficult to interpret in the setting of immunosuppression, fresh tissue is not always available for culture, and culture of fastidious pathogens can be difficult and may take weeks or months to yield a result. Although some microorganisms or their cytopathic effects may be readily identifiable on routine and/or histochemical stains, often these changes are not specific or are sparse in the sample evaluated. Immunohistochemistry and molecular diagnostic techniques have proven to be useful tools in the diagnosis of infectious diseases in tissue samples. These techniques are especially useful in the identification of microorganisms that are present in low numbers, stain poorly, are fastidious to grow, are noncultivable, or exhibit an atypical morphology. It is important to remember that there may be widespread occurrence of common antigens among bacteria and pathogenic fungi, and both monoclonal and polyclonal antibodies must be tested and evaluated for possible cross-reactivity with other organisms. In summary, immunohistochemistry, in situ hybridization, and polymerase chain reaction should be regarded as complementary diagnostic methods for use in the diagnostic pathology laboratory. Each laboratory needs to consider their advantages and limitations as they apply to individual cases and overall laboratory needs.