FIG 4.

CD4 interaction and sCD4 neutralization of CRF01_AE variants. (A) Normalized amounts of radiolabeled wild-type and mutant gp120 glycoproteins were immunoprecipitated with CD4-Ig as described in Materials and Methods for 1 h at 37°C. The precipitates were washed, run on SDS-polyacrylamide gels, and analyzed by densitometry. Fold increase in the binding of gp120 variants to ligands was normalized to wt. Data shown represent the means ± SEM from four independent experiments. Statistical significance was tested using the unpaired t test (ns, not significant; *, P < 0.05; ***, P < 0.001). (B) Normalized amounts of recombinant HIV-1 virions expressing luciferase and bearing different Env mutations were incubated with serial dilutions of sCD4 for 1 h at 37°C before infecting Cf2Th-CD4/CCR5 cells. Luciferase activity in cell lysates was measured to determine the infectivity. Infectivity was normalized to 100% in the absence of the ligand. Data shown are representative of results from at least three independent experiments, performed in quadruplicate. ns, not significant; ****, P < 0.0001.