Some observations on the binding properties of alfalfa mosaic virus to polystyrene and its significance to indirect ELISA.

The adsorption and retention properties of native (unfixed) and glutaraldehyde-fixed alfalfa mosaic virus (AMV) antigens to the polystyrene of ELISA plates were studied using [35S]-labelled virus preparations. It was shown that adsorption was a temperature-dependent, relatively slow process which varied between different AMV isolates. The amount of virus antigen adsorbed was dependent on the type and pH of the suspending buffer. Although native virus antigen adsorbed very efficiently at high pH when the particles had dissociated, significant amounts also adsorbed at pH 7.0, or lower. However, glutaraldehyde-fixed virus particles which retained their integrity even at pH as high as 9.6, adsorbed much more efficiently than native virus antigen above pH 9.0, but hardly at all around pH 7.0. The wide variation in adsorption of AMV antigen to microtitre plates under even slightly different conditions had significant influence on ELISA readings, which calls for extreme caution in interpreting serological results from indirect ELISA when antigen is used to coat the microtitre plates.