Intracellular and extracellular virus maturation shown by infection of hPBMC with lysates and supernatants of NP-2/CCR5 cultures. Seven days after infection, NP-2 cells were trypsinized, washed with PBS and lysed by 0.001% Triton X-100 followed by one cycle of freeze-thawing step. Lysates were titrated at five-fold dilution steps on hPBMC. Supernatant culture fluids from hPBMC infections were collected at day 7 and production of RT was analyzed with undiluted supernatants. The RT cut-off detection level was 50 pg/ml and values above 1000 pg/ml could not be separated. Dark grey bars represent mean virus production in NP-2/CD4/CCR5 cells and. light grey bars represent virus production in NP-2/CCR5 cells. White bars represent virus production measured by RT in PBMC infected with cell lysates diluted 1:5 from infected NP-2/CCR5 cells. Positive syncytia induction (SI) are indicated with +. Means of RT production in duplicates of infection are indicated.