CHARACTERIZATION OF THE IMMUNE-RESPONSE OF VOLUNTEERS VACCINATED WITH A KILLED VACCINE AGAINST HEPATITIS-A

To characterize the immune response elicited by the hepatitis A virus (HAV) vaccine, the sera of 79 subjects who received two vaccine doses at an interval of 1 month and a booster dose 6 months after the first dose, were analysed by ELISA, radioimmunofocus inhibition test (RIFIT) and by a competition monoclonal antibody assay using two neutralizing mAbs (K3-4C8 and B5-B3), which recognize different epitopes. The data show that 93.6% of the volunteers responded after one dose, as detected by ELISA. After the second dose, 100% seroconversion (total Ig) was achieved and most of the vaccinees had neutralizing antibodies. Furthermore, these antibodies are able to inhibit the binding of mAbs K3-4C8 and B5-B3 to the HAV virus, indicating that they recognize two major neutralizing epitopes identified on infectious virions. Using a standard commercial radioimmunoassay test, 100% of the subjects were found positive after the third dose. These different methods of titration were also performed on sera of convalescents and immune serum globulin (ISG) recipients. Although the level of antibodies in convalescents is significantly higher than in vaccinees or in ISG recipients, the relative amount of neutralizing antibodies quantified by the competition monoclonal antibody assay is equivalent for the groups tested.