(A,B) Viruses bound to protein-binding plates were incubated with Ab at axconcentration that neutralizes 90% of free virus (shown in (A)). Cf2Th CD4+CCR5+ target cells were then added to the viruses either in the presence of Ab or after washing the virus extensively. The virus-cell mixture was then incubated at 37°C for 1 hour to allow entry, after which cells were trypsinized to halt entry and further cultured for two days. Infectivity was measured by luciferase activity. For the absolute infection values, see Figure S3. (B) The reversibility of inhibition was calculated by dividing the infectivity of washed virus by the infectivity of unwashed virus. Data are represented as mean +/− SEM.. (C) Correlation between the reversibility of inhibition of the J3Hx(197,HT,N) virus (corrected for the reversibility of Ab-Env binding) and the PF measured on the AD8 Env. Spearman rank-order correlation coefficient, rS; P value, two-tailed T test. Figure 6 is related to Figure S3.