Figure 6

R5 to X4 switch. Time evolution of the concentrations of uninfected T-cells (◇) and viruses (+), during R5 to X4 switch, occurring at time t ≈ 900. After the appearance of the X4 phenotype a continuous slow decline in CD4+ T-cells level leads to AIDS phase (CD4 counts below 200 cells/ml). We set μ ≈ 0.001.