The use of ferritin-conjugated antibodies in electron microscopy

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.

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.

Evaluation of IgG molecules, Fab' fragments and IgG-horseradish peroxidase conjugates as surface labels for freeze-etched membranes

Sheep red blood cell (SRBC) ghosts were incubated with preparations of anti-SRBC IgG, antigen-binding fragments of IgG (Fab') or IgG coupled to horseradish peroxidase (HRPO). Frozen samples of the labelled ghosts were deep-etched and replicated with platinum-carbon to visualize their surface features in the transmission electron microscope. The surfaces of control ghosts contain a very low number of 'background' particles (42 +/- 8 particles/micron 2) that vary in size from 4.5 to 25 nm. After labelling with whole IgG the density of surface particles (average diameter 12.3 nm) increases dramatically to 480 +/- 54 per micron 2. Fab'-labelled ghosts exhibited both significantly fewer (87 +/- 14 particles/micron 2) and smaller (average diameter 9.8 nm) surface particles. Ghosts labelled with IgG-HRPO conjugates possessed 590 +/- 45 particles/micron 2 with an average diameter of 15.3 nm. When these ghosts were incubated with diaminobenzidine and hydrogen peroxide the average size but not the density of the particles increased. Based on these and other observations we conclude that an organic surface marker for freeze-etched membranes has to have a diameter of greater than 15 nm if it is to be consistently seen over extended areas and against the background granularity of the surface of a red blood cell ghost. Somewhat better resolution may be expected if markers consisting of inorganic crystals with a distinct shape and coupled to Fab' fragments can be made.

On the interfibrillar matrix of the pseudo-exfoliation material

Lenses with pseudo-exfoliation (PE) were suspended in a 10% solution of ferritin. In order to retain ferritin at the surface of the PE material during the preparation for the subsequent transmission electron microscopy, some of the lenses were coated with a thin layer of gelatin before the application of the ferritin solution. It was found that ferritin particles to a certain extent penetrated into the PE material. But the concentration of ferritin was much higher in the gelatin coating than in the PE material. The concentration changed stepwise at the interface between the gelatin and the PE material. The ferritin particles in the PE material were mainly found adjacent to the PE fibrils, and there was a certain tendency towards a linear arrangement of the particles. In some specimens, in which thin filaments were found in the interfibrillar space, the ferritin was found mainly along these filaments. The results are interpreted in light of earlier works in which other tracers have been applied. The marked lower concentration of ferritin in the PE material than in the gelatin coating, and the stepwise fall in concentration at the interface between the two materials, seem to confirm the presence of an interfibrillar matrix of the PE material.

The electron microscopic localization of nephrotoxic antibodies in isolated glomeruli

Scanning electron microscopy showed that most glomeruli isolated by sieving from normal and nephrotoxic rats were cleanly decapsulated and undisrupted. An anti-IgG antibody-horesradish peroxidase conjugate was applied to such isolated glomeruli and also to slices of renal cortex which were sebsequently embedded in epoxy resin. Linear staining along the glomerular basement membranes of nephrotoxic rats was evident and subendothelial electron-dense deposits were shown to contain anti-glomerular basement membrane antibody. Whereas the linear reaction was faint and limited to superficial parts of glomeruli in tissue slices, it was intense and present in most regions of all of the isolated glomeruli. Thus, the fine details of the distribution of intraglomerular antibody are more clearly and consistently demonstrated in isolated glomeruli than in kidney slices.