Comparison for purposes of cut-off determinations: A Nunc Polysorp Elisa plate coated with Recombinant HIV antigens (p24 antigen with HIV envelope segment derived from HIV Types 1 & 2 as juxtaposed with three HIV env Type O constructs) .
Antigen coated wells were incubated with a serially diluted serum from an HIV infected individual (serum dilution range, 1:200 through to 1 :100,000) for 60 minutes at room temperature. The wells were then washed 3x using washing buffer (PBS-Tween) and incubated for 30 minutes with an anti-human horseradish peroxidase enzyme conjugate (Sigma), washed 3x and the color developed for 30 minutes with substrate (o-phenylenediamine) and readings taken at 450 nm