Immune electron microscopy


Immune electron microscopy is a variation of electron microscopy. It is applied for diagnosis of many viral infections. A difficult procedure, IEM was developed as a diagnostic aid for detecting and identifying transmissible gastroenteritis virus and rotavirus in fecal and intestinal contents from cases of gastroenteritis in young pigs. IEM is one of the fastest and most sensitive methods for the detection and diagnosis of viruses. This technique is based on formation of immune complexes of the virus with its corresponding antibody.

Procedure

IEM is used to localize molecules at the ultrastructural level by labeling them with specific antibodies, which are visualized by electron-opaque markers attached to them. The effect is to produce an electron-dense label at the site of the antigen-antibody reaction. When the antigen is located inside of the cell, then transmission electron microscopy is required to see it. The labeling can be done pre-embedding or post-embedding.
When the antigen in question is located on the surface of the specimen, scanning electron microscopy can be used to see it. The electron dense label can then be viewed using the back scatter image on an appropriately equipped microscope.

Application

Although IEM is a specific, sensitive, and quantitative assay for hepatitis A antigen and antibody to HA Ag, its practicality for large scale testing is limited. In 1973, Feinstone et al. used IEM to examine stool specimens taken from prison volunteers infected with the Willowbrook MS-1 strain of hepatitis A virus. A well-documented and a highly sensitive virus detection technique, IEM has also been found to be highly effective for potato viruses. IEM also has been used for detecting plant viruses.