Maturation of immunoglobulin G avidity after rubella vaccination studied by an enzyme linked immunosorbent assay (avidity-ELISA) and by haemolysis typing.

Two tests were introduced recently for assessment of the avidity of rubella immunoglobulin antibodies. In the quantitative test--avidity-enzyme linked immunosorbent assay (ELISA)--IgG antibodies obtained from individuals shortly after primary infection with rubella virus are distinguished from those with past immunity by their antigen-elution characteristics. This method uses agents that disrupt hydrophobic bonds in proteins [Kamoun PP (1988): Denaturation of globular proteins by urea: Breakdown of hydrophobic bonds? Trends in Biological Sciences 13:424-425.]. In the semiquantitative, presumptive test--haemolysis typing--the low-avidity rubella-IgG antibodies are distinguished from the high-avidity antibodies by the quality of their haemolytic zones in a radial haemolysis test. In the present study, both tests were applied to sera taken before and after vaccination with two different strains (Cendehill or RA 27/3) of live attenuated rubella virus. It was found that after vaccination of previously nonimmune subjects, IgG synthesized during the first 2 months had a very low avidity; IgG avidity increased dramatically during the subsequent 4 months and less markedly between 6 and 12 months after vaccination. On the contrary, the initially high IgG avidity of previous immune vaccinees remained at an elevated level postvaccination. These results provide a basis for identification of recent primary rubella virus infections, or vaccination reactions, by the avidity of specific IgG and also for their separation from rubella reinfections.