Effect of cyclosporine A on the infectivity of recombinant viruses. Target cells, [U373-X4 (filled green circles), P4 cells (open black circles), MTR-R5 cells (filled red circles), CEM cells (filled purple circles), and H9 cells (filled blue circles)] were cultured in the presence of the indicated serial dilutions of CsA and infected with 100 ng p24/ml (all recombinant viruses except NL4-3) or 20 ng p24/ml (NL4-3) of the indicated recombinant viruses. Luciferase activity (RLU) expressed by target cells was determined 40 h after infection. The results are expressed as a percentage of luciferase activity in cells cultured in the absence of CsA. The results shown are the mean ± SEM for 6 independent experiments (U373-X4, P4, MT4-R5) or 3 independent experiments (CEM, H9).