MONOCLONAL-ANTIBODIES WHICH RECOGNIZE THE ACIDIC CONFIGURATION OF THERABIES GLYCOPROTEIN AT THE SURFACE OF THE VIRION CAN BE NEUTRALIZING

Around 15% of our anti-glycoprotein monoclonal antibodies (MAbs) faile d to neutralize the infectivity of the rabies virus during a 1-hr incu bation at room temperature. In previous studies, we have demonstrated that it is possible to induce a massive conformational change of the g lycoprotein population by incubating the virus at acidic pH. The confo rmational change is reversible and consequently viral infectivity is n ot affected by transient exposure at acidic pH. The proportion of glyc oproteins in acidic or neutral configuration depends on the pH which m eans that even at neutral pH some glycoproteins transiently adopt the acidic configuration and vice versa. Here we report that some of our n onneutralizing MAbs recognize the acidic form of the glycoprotein at t he virion surface. After incubation of the virus at pH 6.4, most glyco proteins are in the acidic configuration. Further 1-hr incubation with these MAbs at the same pH resulted in more immunoglobulins being atta ched to the virus and consequently neutralization was induced. It was also possible to induce neutralization with the same MAbs by incubatio n at neutral pH for a longer period or at a higher temperature. Mutant s resistant to neutralization by these MAbs could be selected. Mutatio ns confering resistance to neutralization were not localized in previo usly described antigenic sites and did not modify these sites at dista nce. They had no effect on the pathogenic power of the virus. Either t hey are situated in the epitope or they modify the epitope, so that it is no longer recognized by the antibody on the acidic configuration o f the protein. Alternatively, these mutations may stabilize the protei n in its neutral configuration. In addition, these experiments confirm our previous finding that neutralization requires the fixation of a l arge number of immunoglobulins on the virus, irrespective of the regio n of the protein recognized by the antibody. (C) 1995 Academic Press, Inc.