Further Studies on the Mechanism of Rabies Virus Neutralization by a Viral Glycoprotein‐Specific Monoclonal Antibody, #1‐46‐12

We previously reported that a conformational epitope‐specific monoclonal antibody (mAb; #1‐46‐12) neutralized the rabies virus by binding only a small number (less than 20) of the antibody molecules per virion, while a linear epitope‐specific mAb (#7‐1‐9) required more than 250 IgG molecules for the neutralization. We also isolated both the epitope‐negative (R‐31) and ‐positive (R‐61) escape mutants that resisted mAb #1‐46‐12. Co‐infection studies with wild type (wt) and R‐61 mutant have shown that although the infectivity of R‐61 mutant was not affected by the binding of about 300 IgG molecules per virion, incorporation of a small number of wt G protein into the R‐61 virion resulted in dramatic loss of the resistance. In this study, we further investigated properties of the mutant G proteins. The R‐61 G protein lost reactivity to the mAb when solubilized, even keeping a trimer form, suggesting that membrane‐anchorage is essential for the maintenance of its epitope‐positive conformation. On the other hand, incorporation of wt G proteins into the R‐31 virions did not affect their resistance to the mAb very much. Although we have not so far found the presumed conformational changes induced by the mAb‐binding, we think that these results are not inconsistent with our previously proposed novel model (referred to as a domino effect model) for the virus neutralization by mAb #1‐46‐12 other than a classical spike‐blocking model, which implicates successive spreading of the postulated antibody‐induced conformational changes of G protein to the neighboring spikes until abolishing the host cell‐binding ability of the virion.