FIG. 4.

Inhibition of sgp120 and sCD4-induced sgp120 binding to the target cell coreceptor CXCR4 by CV-N. Binding of CV-N-treated sgp120 to A2.01 cells (CD4 negative, CXCR4 positive) upon activation by sCD4 was determined by a flow cytometry-based sgp120-binding assay (see Materials and Methods). Incubation of the cells with sgp120 results in acquisition of anti-gp120 MAb–FITC staining. (A) Background (A2.01 cells without sgp120, CV-N, and sCD4). MFI value, 8.0. (B) Effects when sgp120 was used as positive control. MFI value, 16.9. (C and D) Effects when sgp120 was preincubated with sCD4(C) and CV-N (D). MFI values, 29.4 (C) and 7.7 (D). (E) Effects when sgp120 was first preincubated with CV-N and then activated by incubation with sCD4. MFI values, 8.6. (F) sgp120 was first activated by sCD4 and then incubated with CV-N. MFI value, 7.8. The molar ratios of sgp120 to CV-N and sCD4 are 1 to 4 and 4, respectively, in the final mixtures. At least 10,000 events were acquired for each sample.