Sample Preparation/Fixation

Abstract

This chapter discusses the immunocytochemical methods in current use for light and electron microscopy. Immunocytochemistry is the identification of a tissue constituent in situ by means of a specific antigen–antibody reaction tagged by a visible label. Two new reagents used in immunocytochemistry are—a large glycoprotein, avidin, from egg white and a small protein, biotin, which is a vitamin found in egg yolk, among other sites. Avidin has a high affinity for biotin; one molecule can bind four biotin molecules. Biotin also binds to the Fc portion of immunoglobulins, each biotin molecule having one binding site but several biotin molecules being bound to one immunoglobulin molecule. Both avidin and biotin can be labeled with fluorescent, enzyme, ferritin, or gold labels. Numerous combinations of avidin, biotin, and antibody can be built up.