Enzyme-Labeling of Antibodies and Their Fragments for Enzyme Immunoassay and Immunohistochemical Staining

Abstract

The use of an enzyme as a label has a number of advantages over the use of other labels in both immunohistochemistry and immunoassay. Immunofluorescence techniques are not suitable for ultrastructural research on cells, and ferritin-labeled antibodies allow only electronmicroscopic studies. By contrast, enzyme-labeled antibodies permit localization of cellular antigens in relation to tissue structures under light microscope and also demonstration of cellular antigens at an ultrastructural level by electronmicroscopy. Antibody or antibody fragments labeled with enzymes of small molecular weight can more readily permeate cells of tissue sections than ferritin-labeled antibodies. The color of tissue sections prepared by immunoenzymatic techniques is stable for years, while immunofluorescence of tissue sections decreases rapidly when exposed to light. Radioisotope-labeled reagents decay with time; there are health hazards due to radio isotopes; and disposal of radioactive waste is becoming increasingly difficult. By contrast, enzyme-labeled antigens and antibodies are stable for months or even years and there are no problems either of health hazards or of waste disposal with appropriate choice of enzymes and substrates. Under favourable conditions, enzyme immunoassays may be even more sensitive than radioimmunoassays (1). Enzyme-labeled antigens and antibodies have found increasing use during the past decade, reinforced by improvements in enzyme-labeling methods.