Differences in reverse transcriptase activity versus p24 antigen detection in cell culture, when comparing a homogeneous group of HIV type 1 subtype B viruses with a heterogeneous group of divergent strains

Failure to detect infection with HIV-1 non-B subtypes in some antibody screening assays has been shown, To date, however, no studies have been published evaluating the capacity of standard tests to quantify replication of divergent HIV-1 in cell culture, Reverse transcriptase (RT) activity and p24 antigen assays are the two methods most commonly used for this purpose, A homogeneous panel of HIV-1 subtype B viruses from northern Italy and a heterogeneous panel of diverse genetic subtypes (A to F and 0) from different regions of the world were cultured under identical conditions, A new nonradioactive RT assay was used as a basis for comparison to evaluate the capacity of two p24 assays to quantify viral growth in both panels. Comparison of the p24 amount/RT activity (p24/RT) ratios showed that ratios in the subtype B panel tended to be markedly higher than in the diverse subtype panel, Greatest variation was seen with one of the subtype O isolates, where up to a 400 times lower ratio was obtained compared with the average ratio for the subtype B panel, In addition, one Thai subtype B virus also gave a markedly reduced ratio, Furthermore, comparison between the two p24 assays showed different abilities to detect p24 from different HIV-1 isolates, We discuss limitations for the use of anti-HIV-1 p24 antibodies produced by immunization with subtype B p24 in p24 assays.