Immunochemical studies of polioviruses: identification of immunoreactive virus capsid polypeptides

Investigation of the immunological reactions with individual poliovirus capsid polypeptides of antisera and monoclonal antibodies raised against poliovirus type 3 antigens are described. Virus polypeptides were separated by electrophoresis, transferred electrophoretically to nitrocellulose sheets and treated with antibody preparations. Antibody binding specifically to the virus polypeptides was then detected by application of 125I-labelled anti-immunoglobulin followed by autoradiography. The technique readily enabled the identification of the polypeptides recognized by the antibody. Antibodies present in polyclonal, type-specific neutralizing sera to poliovirus type 3 bound to the two largest capsid polypeptides (VP1 and VP2) of the homotypic poliovirus, and also to the VP1 of poliovirus type 1 and type 2. There was no obvious difference between the antibody binding patterns obtained with neutralizing and non-neutralizing antisera or between C-specific and D-specific antisera. VP1 appeared to be the immunodominant virus polypeptide. Among monoclonal antibodies specific for the C antigen of poliovirus type 3, a proportion reacted homotypically with the VP1 of poliovirus type 3. Other monoclonal antibodies of C antigen or D antigen specificity, or which reacted both with D and C antigens, some of which had potent virus-neutralizing activity, failed to give demonstrable binding reactions. The non-correlation of neutralization and immunoblot reactivity suggests that sequence determinants alone do not mediate virus neutralization which may depend on antigenic determinants specified by complex conformational arrangements of the virus capsid proteins.