The physico-chemical properties and immunogenicity of experimental
vaccines against
foot-and-mouth disease (FMD) and
poliomyelitis, prepared by treatment of the viruses with
N-acetylethyleneimine (AEI),
formaldehyde or
neutral red, have been studied. None of these
reagents affects the rate of sedimentation of the particles or their reaction with antibody against the major immunogenic sites. FMD
vaccines prepared by inactivation with AEI or
neutral red, behaved like the untreated virus, in that they were disrupted on lowering the pH below 7. The
RNA of the AEI-inactivated virus was degraded into slowly sedimenting molecules. Unlike AEI-inactivated virus, from which all the
RNA could be extracted with
phenol-SDS, the recovery from the
neutral red inactivated virus was variable and was sometimes as low as 40%; this
RNA gave a heterogenous profile in
sucrose gradients. The
capsid proteins in the AEI preparation migrated in SDS-PAGE to the same positions as those of untreated virus, but in the
neutral red preparation there was evidence of cross-linking. In contrast, the
formaldehyde-
inactivated vaccine was stable below pH 7 and the
RNA could not be released by extraction with
phenol-SDS at pH 5, because the
capsid proteins had become cross-linked and/or linked to the
RNA. As with foot-and-mouth disease virus (FMDV), poliovirus which had been inactivated with
formaldehyde did not release its
RNA on extraction with
phenol-SDS and the
capsid proteins were also cross-linked. Surprisingly, although AEI cleaved the
viral RNA slowly in situ, the virus was no longer infectious after 6 h.
Neutral red did not reduce the infectivity of the virus. All of the preparations gave similar levels of
neutralizing antibody after a single inoculation. The high levels obtained with the
formaldehyde-
inactivated vaccines have implications for the processing of fixed particles by the antigen-presenting cells.