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 be en published evaluating the capacity of standard tests to quantify rep lication of divergent HIV-1 in cell culture, Reverse transcriptase (RT ) activity and p24 antigen assays are the two methods most commonly us ed for this purpose, A homogeneous panel of HIV-1 subtype B viruses fr om northern Italy and a heterogeneous panel of diverse genetic subtype s (A to F and 0) from different regions of the world were cultured und er identical conditions, A new nonradioactive RT assay was used as a b asis for comparison to evaluate the capacity of two p24 assays to quan tify viral growth in both panels. Comparison of the p24 amount/RT acti vity (p24/RT) ratios showed that ratios in the subtype B panel tended to be markedly higher than in the diverse subtype panel, Greatest vari ation was seen with one of the subtype O isolates, where up to a 400 t imes lower ratio was obtained compared with the average ratio for the subtype B panel, In addition, one Thai subtype B virus also gave a mar kedly reduced ratio, Furthermore, comparison between the two p24 assay s showed different abilities to detect p24 from different HIV-1 isolat es, We discuss limitations for the use of anti-HIV-1 p24 antibodies pr oduced by immunization with subtype B p24 in p24 assays.