STRUCTURE AND IMMUNOGENICITY OF EXPERIMENTAL FOOT-AND-MOUTH-DISEASE AND POLIOMYELITIS VACCINES

The physico-chemical properties and immunogenicity of experimental vac cines against foot-and-mouth disease (FMD) and poliomyelitis, prepared by treatment of the viruses with N-acetylethyleneimine (AEI), formald ehyde or neutral red, have been studied None of these reagents affects the rate of sedimentation of the particles or their reaction with ant ibody against the major immunogenic sites. FMD vaccines prepared by in activation with AEI or neutral red behaved like the untreated virus, i n 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 extracte d with phenol-SDS, the recovery from the neutral red inactivated virus was variable and was sometimes as low as 40%; this RNA gave a heterog enous profile in sucrose gradients. The capsid proteins in the AEI pre paration migrated in SDS-PAGE to the sane positions as those of untrea ted virus, but in the neutral red preparation there was evidence of cr oss-linking. In contrast, the formaldehyde-inactivated vaccine was sta ble below pH 7 and the RNA could not be released by extraction with ph enol-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 (FMD V) , poliovirus which had been inactivated with formaldehyde did not rele ase its RNA on extraction with phenol-SDS and the capsid proteins were also cross-linked. Surprisingly, although AEI cleaved the viral RNA s lowly in situ, the virus was no longer infectious after 6 h. Neutral r ed did not reduce the infectivity of the virus. All of the preparation s gave similar levels of neutralizing antibody after a single inoculat ion. The high levels obtained with the formaldehyde-inactivated vaccin es have implications for the processing of fixed particles by the anti gen-presenting cells.