Gold-labelled antibody decoration (GLAD) in the diagnosis of plant viruses by immuno-electron microscopy

Purification and immuno-gold labeling of lily mottle virus from lily leaves

Lily mottle virus (LMoV) is prevalent in Lilium species worldwide causing dwarfing, flower breaking, and reduced bulb yield. In this paper, an easy to use and efficient procedure is described for purification of LMoV from lily leaves. The resulting sample is characterized by a 260/280 nm absorbance ratio of 1.20 at a concentration of 1.27 mg/ml. The procedure results in high protein purity and particle integrity as shown by UV-spectrophotometry, polyacrylamide gel electrophoresis (PAGE), Western blotting, reverse transcriptase (RT)-PCR and transmission electron microscopy (TEM) in combination with immuno-gold labeling. This is the first time that an immuno-gold labeling (IGL) assay was performed to identify a virus of lily. Purified products can be used as a source of antigen in the preparation of antibodies against LMoV and may assist in the development of a diagnostic test for LMoV and in epidemiological surveys.

Origins of electron microscopy and viral diagnosis

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Immuno-electron microscopical detection of tomato spotted wilt virus and its nucleocapsids in crude plant extracts

Tomato spotted wilt virus (TSWV) particles were identified in thin sections and in crude extracts of leaves from plants infected with different TSWV isolates, using gold labelled protein A and antibodies prepared against purified virus particles or against nucleocapsid preparations. In addition, both in thin sections and in dip preparations aggregates were detected using either gold-labelled antiserum. These aggregates were not detected using antisera against envelope proteins or against the non-structural protein NSs. They were the only detectably labelled material in preparations made from plants infected by morphologically defective isolates of TSWV, i.e. isolates that did not produce enveloped particles. The aggregates were discerned in dip preparations as cloudy amorphous structures having a cottonwool boll-like appearance. These 'cotton bolls' were interpreted as being the in vitro structures of the nucleocapsid aggregates occurring in plant cells infected by isolates maintained by mechanical inoculation and are the only structures in cells infected by morphologically defective isolates (Ie, 1982; Kitajima et al., 1992). The detection of the 'cotton boll-like' structures in crude extracts provides an adequate and rapid method to establish the presence of nucleocapsid aggregates in cells of infected plants, irrespective of whether they are infected by morphologically defective isolates or not.

Negative staining in the detection of viruses in clinical specimens

Viruses have unique morphology and are therefore good candidates for negative staining. Negative staining with phosphotungstic acid (PTA) or uranyl acetate has facilitated the detection of many viruses in clinical specimens. Enhancement procedures have included the use of centrifugation and agar diffusion for concentrating virus particles, the use of solid phase capture reagents to trap virus particles and the use of secondary antibodies and electron dense markers to help visualize them. Techniques currently in use and employing negative staining include direct EM, immune electron microscopy (IEM), solid phase immune electron microscopy (SPIEM), colloidal gold-labeled protein A (PAG), solid phase IEM employing a second decorator antibody (SPIEMDAT), and solid phase IEM using colloided gold-labeled secondary antibodies (SPEIMDAGT). IEM methods assist with the detection of small viruses or viruses present in low numbers while PAG offers increased sensitivity over direct EM and IEM. In our experience the serum-in-agar (SIA) method is the most sensitive of the PAG IEM techniques for detection of rotavirus particles in clinical specimens. SPIEMDAT enhances the detection of small viruses which are often missed by other techniques due to background staining in specimens. SPEIMDAGT employing colloidal gold-labeled secondary antibody has increased sensitivity and offers the advantage of detecting viral antigen when whole virus particles are not visible. IEM techniques have recently been used for typing viruses using either monospecific antisera or monoclonal antibodies and colloidal gold-labeled secondary antibody.

Comparison of three protein A-gold immune electron microscopy methods for detecting rotaviruses

Three immune electron microscopic (IEM) methods employing protein A-colloidal gold (PAG) were compared with direct electron microscopy (DEM) and direct IEM (DIEM) techniques for their abilities to detect simian rotavirus (SA11) and human rotavirus. Using PAG IEM the number of rotavirus particles per grid square was 10 to 50 times and 2 to 5 times higher than observed with DEM and DIEM, respectively. A comparison of sensitivities among the three PAG IEM methods showed that the trapping efficiency for SA11 and human rotavirus was significantly enhanced by a serum-in-agar (SIA) method. The SIA method appeared to be a more reliable and sensitive alternative for detection and quantitation of viral particles.

Use of gold IgG complexes and human antisera for electron microscopic identification of hepatitis A virus and polioviruses

An indirect immunogold staining technique was used for identification of hepatitis A virus and poliovirus types 1,2 and 3 by electron microscopy. Human convalescent antisera against hepatitis A virus and the three poliovirus types were used as primary antibodies and goat anti-human IgG gold complexes, with an approximate gold granule size of 15 nm, as secondary antibody. Hepatitis A virus was specifically labelled with the homologous antiserum. No labelling was observed when antiserum against poliovirus or other negative control sera were used as primary antibody. Poliovirus types 1, 2 and 3 were specifically labelled with a human serum with high titres of antibody against all three virus types. The use of type-specific antisera made it possible to distinguish types 1, 2 and 3 from each other, although slight cross-reactions occurred. The results indicate that gold IgG complexes in conjunction with human antisera may be used for identification of small spherical viruses.

Immunonegative stain techniques for electron microscopic detection of viruses in human faeces

Immune electron microscopy techniques have for some years been applied to detection of viruses in clinical specimens, especially faecal samples, as both sensitivity and specificity are improved by use of specific antibody. The following review describes in detail different preparation methods and illustrates some of the results that may be obtained.

Development of a sensitive protein A-gold immunoelectron microscopy method for detecting viral antigens in fluid specimens

Protein A-colloidal gold immunoelectron microscopy (PAG IEM) has been employed to specifically detect rotavirus and enterovirus antigen in negatively stained fluid specimens. Unlike other IEM methods, PAG IEM can detect not only viral antigen associated with morphologically recognizable particles but also viral antigens of unrecognizable ultrastructure. This rapid and sensitive immunoassay was found to be applicable to virus-infected stool specimens as well as partially purified virus preparations. The sensitivity of viral antigen detection by PAG IEM was 2- to 40-fold greater than direct IEM and 200- to 1,000-fold greater than direct electron microscopy. In addition, PAG IEM appears to offer a more reliable and sensitive alternative to standard IEM for detection and quantitation of viral antibody.

Specific labelling of human rotaviruses and adenoviruses with gold-IgG complexes

Human rotaviruses and adenoviruses were specifically labelled by an indirect immuno gold staining technique for electron microscopy. Rabbit antisera against human rota- and adenoviruses were used as the primary antibody and goat anti-rabbit IgG-gold complexes as secondary antibody. Optimal conditions for the procedure were established by testing serial dilutions of the antisera. Precoating of electron microscopy grids with bovine rotavirus antibody decreased nonspecific background staining and at the same time increased slightly the number of virus particles adsorbed to the grid. Noncultivable enteric adenoviruses showed no antigenic relationship to adenovirus type 2 and 6 from cell culture material when tested by this gold labelled antibody decoration technique. However, a slight cross-reaction was observed between adenovirus type 2 and type 6.

An evaluation of some factors important for maximising sensitivity of plant virus detection by immuno-electron microscopy

We report the results of a comparison of the variations to the basic technique developed by Derrick and called 'serologically specific electron microscopy' by him. We have found that the reaction time of the antibody-coated grid with the virus preparation (virus acquisition time) is one of the key factors in determining the efficiency of the method at trapping virus particles. The lower the virus concentration, the longer the reaction time should be. The use of protein A to pretreat the grids before coating with antiserum did not appear to be of benefit under our conditions.

Gold-IgG complexes improve the detection and identification of viruses in leaf dip preparations

An immunoelectron microscopic method is described for rapid detection and identification of plant viruses in leaf-dip preparations by specific labelling with gold-IgG complexes. The process takes only 10 min and markedly improves the identification of viruses, particularly spherical ones including luteoviruses in leaf dips over simple antibody decoration.

Electron microscopic identification of rotavirus group antigen with gold-labelled monoclonal IgG

Colloidal gold was complexed with monoclonal IgG to the inner capsid of human rotavirus. The complex was then used as an immunoelectron microscopic marker to identify the location of the group-specific antigen of rotavirus.