Analysis of the vaccinating group specificity a of HBsAg with monoclonal antibodies. Identification of continuous and discontinuous epitopes.

The group specificity a of HBsAg is responsible for the induction of protective antibodies. Several synthetic peptides for vaccination are in preparation. It is not known if the structure of the epitope(s) implied in specificity a is continuous or discontinuous. For this analysis, we have prepared six monoclonal anti-a antibodies (all belonging to the IgG1 subclass) which precipitated native HBsAg and agglutinated sensitized red blood cells. The antibody affinities ranged from 1.2 X 10(9) to 10 X 10(10) 1/M. These monoclonal antibodies were comparatively tested against native radioiodinated HBsAg and polypeptides obtained from HBsAg after reduction and alkylation. Two antibodies with low affinity continued to bind about 40% of polypeptides (compared to 94% retained by polyclonal antibodies). Three antibodies with higher affinity did not bind any polypeptide under the same conditions. When an inhibition technique was used, the two antibodies binding the polypeptides could be inhibited by polypeptides in their reaction with HBsAg. For the other antibodies, polypeptides did not inhibit the reaction with HBsAg. These results show that continuous and discontinuous epitopes are implied in specificity a of HBsAg. Therefore, for effective synthetic vaccines, mere synthesis of peptides corresponding to selected sequences of the primary structure of the protein may not be sufficient and a sophisticated mimicking of a conformational epitope might also be necessary.