Antibody avidity measurement and immune complex dissociation for serological diagnosis of vertically acquired HIV-1 infection.

Differences in avidity between HIV-1 antibodies transmitted passively and antibodies synthesized by children born to HIV-1-positive mothers can be measured using a commercially available competitive enzyme immunoassay kit. The avidity determination method is based on the competition between an anti-HIV-1-peroxidase-labeled antibody at a stable and known concentration and the anti-HIV-1 antibodies (IgA, IgG, IgM) present in the child's serum at various and increasing dilutions. The shift in the competition/dilution curves between serum samples taken at the third and the sixth month of the child's life showed either the loss or the synthesis of anti-HIV-1 antibodies. The antibody avidity determination combined with a test detecting free or complexed p24 antigen is a workable and inexpensive serological method for the follow-up of children born to seropositive mothers. Combining these two complementary methods, HIV-1 infection has been established at 6 months of age in 13 of 13 infants, and positive results were confirmed by coculture and by PCR. An HIV-1 infection was excluded at 6 months of age in 17 of 17 infants, results otherwise confirmed by virological and clinical follow-up. These new and convenient approaches to the diagnosis of vertically acquired HIV-1 could be used worldwide, including in developing countries.