LONGITUDINAL-STUDY OF AN EPITOPE-BIASED SERUM HEMAGGLUTINATION-INHIBITION ANTIBODY-RESPONSE IN RABBITS IMMUNIZED WITH TYPE-A INFLUENZA VIRIONS

This paper describes a longitudinal study of the antibody specificitie s generated to the haemagglutinin (HA), the major envelope glycoprotei n of type A influenza virus particles, during primary and secondary an tibody responses in rabbits. Two New Zealand White rabbits (no. 191, n o. 192) and an English Half-Lop rabbit (no. 193) were immunized intrav enously with beta-propiolactone-inactivated virus at 0, 28 and 56 days . Haemagglutination-inhibition (HI) antibody specificities were measur ed using neutralizing antibody double escape mutants selected with mon oclonal antibodies (mabs) specific for an epitope in antigenic site A, site B and site D. In this regard the epitope reactivity to these mab s was represented as A(+)B(-)D(-), A(-)B(+)D(-) and A(-)B(-)D(+), wher e ''+'' and ''-'' represent the non-mutated and mutated epitopes respe ctively. The HI response was well developed at 7 days after primary im munization and at this time the response was well developed at 7 days after primary immunization and at this time the response was equally d ivided between all three epitopes. Two rabbits (no. 191 and no. 193), showed a bias to the site B epitope from 14 days onwards, such that ab out half of the total HI activity was to this epitope and the other ha lf was made up of HI antibody to the other two epitopes in approximate ly equal proportions. In the other New Zealand White rabbit (no. 192) a non-biased response extended throughout the primary response and for one week after the second immunization. Apart from this, a bias to a single epitope was clearly evident in all rabbits after the second imm unization, and this constituted up to 70% of the total HI antibody res ponse. The antibody response did not broaden and remained essentially unchanged even after a third immunizing injection. The observed bias t o the site B epitope during the secondary response of HA-specific anti body is in accord with a previous cross-sectional study of nine other rabbits.