Use of protein A-gold complex for specific labelling of antibodies bound to plant viruses. I. Viral antigens in suspensions.
Colloidal gold particles 5 nm in diameter complexed with protein A (pAg) were bound specifically to rabbit antibodies which had reacted with antigens of 12 different plant viruses previously adsorbed to electron microscope (EM) support films. Conditions for highly specific labelling of antigens combined with a low non-specific background were assessed. In antiserum dilution tests, pAg labelling increased by up to four two-fold dilution steps the sensitivity of detecting low amounts of antibodies on virus particles. The pAg complex allowed detection of small antigens having no distinct morphology. The combination of dense antibody coating and pAg labelling substantially increased virus particle dimensions and contrast. This effect was further increased by double-antibody coating of the particles using rabbit anti-virus IgG followed by goat anti-rabbit IgG, prior to pAg incubation. Screening for elongated virus particles at low concentration in crude sap was then facilitated at very low EM magnifications. The pAg technique could be combined with trapping steps by using F(ab')2 fragments instead of complete antibodies for coating the grids.
D000914:Antibodies, Viral / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology; D003102:Colloids; D006046:Gold; D007158:Immunologic Techniques; D008854:Microscopy, Electron; D010942:Plant Viruses / Q000276:immunology* / Q000648:ultrastructure; D013205:Staphylococcal Protein A
D000914:Antibodies, Viral; D000956:Antigens, Viral; D003102:Colloids; D013205:Staphylococcal Protein A; D006046:Gold