Articles
IMMUNOELECTRONMICROSCOPY FOR VIRUS DETECTION AND VIRUS STRAIN IDENTIFICATION
In particular, when used under optimal conditions, IEM appears as sensitive as ELISA.
The best technique consists of the so-called immunosorbent electronmicroscopy (ISEM) followed by a coating of the trapped particles by specific antibodies (decoration) which allows a clearcut identification of these particles.
A modification of the technique was introduced and was called double decoration : it consists of a further coating of the virus specific antibodies (in general from rabbit) by antirabbit immunoglobulins : this technique which results in a considerable increase of the apparent diameter of virus particles allows detection in a larger microscope field at a lower magnification : this is especially interesting when the number of particles present in the infected extracts is very low.
Furthermore, this technique was used for investigating virus strain serological relationships : results were compared to those obtained by single decoration and also to those from agar double diffusion.
Compared to gel diffusion, advantage of double decoration was clear : 4–7 more two-fold dilutions in the homologous and heterologous titres.
Compared to single decoration amplification can be estimated to 2–3 more two-fold dilutions.
The lowest values of RT-SDI result from the double decoration which appears a very suitable technique for detecting relationships between very distant virus strains and has the additional interest of using very low amounts of virus.
It can use crude extracts from infected plants : then, best results are obtained when virus particles are trapped on the grid by antibodies (ISEM) prior to the decoration steps.