Attachment of neutralizing antibodies stabilizes the capsid of poliovirus against uncoating

Poliovirus capsid is rapidly and irreversibly degraded upon treatment in hypotonic buffer at 37 degrees C. However, the attachment of neutralizing antibodies stabilized the virus capsid against degradation by similar treatment. This was demonstrated by the use of antisera to poliovirus from rabbits and other mammalian species. As shown with neutralizing antibodies, the degree of capsid stabilization paralleled the number of bound IgG molecules per virion and the rate of neutralization. Upon acid treatment virus-antibody complexes disaggregated and infectious virus was recovered. Divalent binding of antibodies to the virus surface has been suggested to be a prerequisite for neutralization by cross-linking subunits, thereby preventing virus uncoating. This reaction was mimicked by using chemical cross-linking with a bifunctional reagent. The introduction of intramolecular bridges between adjacent VP1 and VP3 polypeptides was accompanied by a marked drop in infectivity. The treated virus was still able to adsorb to and penetrate into HeLa cells. Physically, intact virus could be reisolated from infected cells, suggesting that the loss of infectivity was probably due to the inhibition of uncoating. Additionally, cross-linked virus was stabilized against treatment in hypotonic buffer. Cleavage of the cross-links by treatment with a reducing agent under mild conditions resulted in restoration of the infectivity.