Summary
The infectivity of poliovirus type 2, neutralized by rabbit γ-globulin, was reactivated by papain digestion. However, virus which had been neutralized by papain-produced univalent 3.5 S Fab fragments was not reactivated by equivalent digestions. Proteolysis with pepsin in the absence of reducing agents, leading to the conversion of 7 S γ-globulin to bivalent 5 S F(ab′)2 fragments, was not capable of reactivating neutralized virus. Infectivity of such complexes was reestablished following the reductive cleavage of F(ab′)2 units into univalent 3.5 S Fab′ fragments. Virus neutralized by enzymatically derived peptic fragments F(ab′)2 could also be reactivated by reduction alone. The infectivity of enzymatically reactivated virus was sharply reduced following reaction with goat anti-rabbit γ-globulin antibody, demonstrating that the enzymatic reestablishment of virus infectivity was not the result of the dissociation of antibody fragments from virus. Inhibition of the reactivation developed in zones of high excess of anti-rabbit γ-globulin as well as with univalent anti-rabbit Fab fragments, indicating that reneutralization did not occur as a result of the formation of secondary immune aggregates. These findings suggest that the reestablishment of neutralization was due to the coupling of the heterologous globulins with Fab fragments attached to virus and that this accessory component provides the structural configuration necessary for virus neutralization.
On the basis of this investigation, it is proposed that the efficiency of virus neutralization is not only affected by the specificity of recognition of the antigen-binding sites, but is significantly dependent on the size and possibly the configuration of the globulin structure.
