Virus release from transfected cells and their infectivity. HeLa-tat III, 293T, and COS7 cells were transfected with mutant and wild type proviral DNAs as indicated. (A) Three days post-transfection, culture supernatants were collected and analyzed by CAp24-ELISA. (B) Normalized amounts of cleared and filtered culture supernatants from the above transfected cells were then used to infect MT4 cells (1 × 105 cells per well in 48-well plate) using 100 ng of CAp24 antigen. The bars indicate infectivity of the virus particles produced from the three different cell lines monitored by CAp24-ELISA.