Introduction: Analysis of samples from Uganda using serologic HIV incidence assays reveal that individuals with subtype D infection often have weak humoral immune responses to HIV infection. It is unclear whether this reflects a poor initial response to infection or a waning antibody response later in infection.
Materials and methods: Samples (N = 2614) were obtained from 114 women aged 18-45 years in the Ugandan Genital Shedding and Disease Progression Study cohort (2001-2009; 82 subtype A, 32 subtype D; median 23 samples/women, range 3-41 samples, median follow-up of 6.6 years). Samples were analyzed using the BED capture immunoassay (cutoff, 0.8 OD-n) and the avidity assay (cutoff, 90% Avidity Index). Antibody maturation was assessed by having the BED capture enzyme immunoassay (BED-CEIA) or avidity value exceed the assay cutoff 1 or 2 years after infection. The waning antibody response was measured by having the BED-CEIA or avidity value fall >20% below the maximum value.
Results: For the BED-CEIA, 8 women with subtype A infection and 3 women with subtype D infection never progressed previously the cutoff value (median, 5.9 years follow-up after infection). Six women with subtype D infection never achieved an avidity index >90%. Subtype did not impact the proportion of women whose assay values regressed by >20% of the maximal value (for BED-CEIA: 33% for A, 41% for D, P = 0.51; for avidity: 1% for A, 6% for D, P = 0.19).
Discussion: The higher frequency of misclassification of individuals with long-term subtype D infection as recently infected using serologic incidence assays reflects a weak initial antibody response to HIV infection that is sustained over time.