[Gelatin particle agglutination (PA) antibody: comparison to neutralizing antibody (NT) and hemagglutination inhibition (HI) antibody and relationship to IgG avidity].

Changes in gelatin particle agglutination (PA), hemagglutination inhibition (HI), and neutralization (NT) antibodies were compared using sera from 124 individuals collected between 3 weeks and 10 years after measles vaccination, and the relationship between these changes and IgG avidity was studied. PA, HI, and NT antibodies peaked 4-5 months after vaccination. The rate of increase in mean antibody titer from 0-1 months after vaccination to peak levels was 1.7-fold for NT, 1.5-fold for HI, and 7.4-fold for PA antibodies. Peak mean antibody titer was 2(11.8) for PA, 2(6.7) for NT and 2(6.7) for HI antibodies. After peaking PA antibodies changed in parallel with NT and HI antibody titers, and correlated strongly with both antibodies (r = 0.801 and 0.840). In contrast, NT and HI antibodies were consistent throughout the period. IgG avidity increased for 4-5 months following vaccination, peaking at 45%, and remaining constant at 40-50% for the next 10 years. PA antibody is strongly influenced by IgG avidity, unlike NT and HI antibodies. Due to the effects of IgG avidity, PA antibodies increase more significantly than NT and HI antibodies as IgG antibodies mature following vaccination, resulting in a weak correlation between PA and NT or HI antibodies. Following the increase in IgG avidity to maturation, PA antibodies correlated strongly with NT and HI antibodies. PA assay detected IgM antibodies against measles virus more efficiently than the NT test. The PA assay thus differs from conventional, commonly used NT and HI assays. PA assay is simple and rapid, making it very useful for detecting measles antibodies provided that its unique features are taken into accounts.