Detection of human immunodeficiency virus type 1 nucleocapsid protein p7 in vitro and in vivo

We developed and evaluated an immunoassay for the detection and quantificat ion of human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein p7 using electrochemiluminescence technology. The assay had a dynamic range of 50 to 20,000 pg/ml and a lower detection limit equivalent to approximately 106.5 HIV-1 RNA copies/ml in culture supernatant, In vitro kinetic replica tion studies showed that the amount of p7 correlated strongly with the amou nt of p24 (R-2 = 0.869; P < 0.0001) and viral RNA (R-2 = 0.858; P = 0.0009) . On the basis of the p7 and RNA concentrations, we calculated the median p 7:RNA ratio to be approximately 1,400 p7 molecules per RNA molecule. HIV-1 p7 could be detected and quantified in culture supernatants of both group M subtype A to E viruses and group O viruses. The presence of p7 in vivo was evaluated in 81 serum samples collected from 62 HN-l-infected individuals, Five samples were p7 positive, whereas 35 samples were HIV-1 p24 positive. sour of the five p7-positive samples were p24 positive as well, p7 could b e detected only when serum HIV-1 RNA levels were greater than 10(6) copies/ ml. Anti-p7 antibodies were found in six samples, and all six were p7 negat ive. In contrast to the in vitro results, it appeared that HIV-1 p7 could n ot be used as a marker for viral quantification in vivo, since more than 90 % of the serum samples were p7 negative, In combination with the low preval ence of anti-p7 antibodies, this may, in turn, be advantageous: the p7 assa y may be a good alternative to the p24 assay as the readout system for dete rmination of neutralizing activity against HIV-1 in serum or other fluids c ontaining anti-p24 antibodies.