Dynamics of Maternal IgG Antibody Decay and HIV-Specific Antibody Synthesis in Infants Born to Seropositive Mothers

We have used a human immunodeficiency virus type 1 (HlV-1)-specific IgG-Fc capture enzyme immunoassay (IgG-CEIA) to elucidate the dynamics of HIV-1 maternal antibody decay and de novo synthesis of HIV-1 antibodies in infants. Two hundred and thirty-nine serum specimens from 77 infants were analyzed by the IgG-CEIA and by two different conventional EIAs. With the IgG-CEIA, IgG was captured by an anti-human IgG monoclonal antibody (3C8) that reacts with all subclasses and was detected by recombinant HIV-1 envelope protein (CBre3)-peroxidase conjugate. Unlike the conventional EIAs, the IgG-CEIA showed a rapid decay of HIV-1-specific antibody in uninfected infants, with decline to background levels by 6 months (T_1/2 [half-life] = 28-30 days). All 69 specimens collected from 39 uninfected infants between 6 and 15 months of age were negative by IgG-CEIA. However, HIV-1 antibodies remained high in infected infants; 20/22 infants (90.9%) with specimens between the ages of 6 to 23 months were positive by IgG-CEIA. Subtracting mean IgG-CEIA optical density values of seroreverting infants from those of HIV-1-infected infants in corresponding age groups provided a model for seroconversion in infected infants, with detectable IgG antibody synthesis starting about 3 months after birth. The IgG-CEIA may be a simple and important tool for early diagnosis of HIV-1 infection in infants at 6 months of age.