Resistance of plasma virus isolates generated from subjects acutely infected with HIV-1 to in vitro control by IFN-α and IFN-β. (A) IFNα (filled circles) and IFNβ (open triangles) IC50 values of virus isolates generated from different subjects during acute HIV infection; and (B) IFNα (filled circles) and IFNβ (open triangles) Vres values of these virus isolates. Each datapoint represents the mean (of results obtained in a minimum of 2 independent IFN inhibition assays) IC50 or Vres value calculated for a given virus isolate. The horizontal lines show the group mean IC50 or Vres values, plus and minus one standard error. (C) Inhibition of the replication of individual HIV-1 isolates at different IFN concentrations. The level of replication of each virus isolate in the presence of different concentrations of IFNα or IFNβ (mean supernatant p24 concentration, expressed as a percentage of the mean p24 concentration in the absence of IFN) was evaluated in a minimum of two independent assays, the mean of results from which is plotted against the IFN concentration, expressed on a linear scale to illustrate viral replication in the presence of high IFN concentrations. Clusters of virus isolates that exhibit shared patterns of relative resistance to control by IFNα and IFNβ are indicated by the bold solid, long-dashed and short-dashed lines.