Inhibition of the gp120-CD4 interaction. (A) A cell-based fusion assay was used to mimic the gp120-CD4 mediated fusion of the viral and host cell membranes. HL2/3 and HeLa-CD4-LTR-β-gal cells were incubated with a two-fold serial dilution of silver nanoparticles and known antiretrovirals. The assay was performed in triplicate; the data points represent the mean ± s.e.m. (B) The degree of inhibition of the gp120-CD4 protein binding was assessed with a gp120/CD4 ELISA capture in the presence or absence of silver nanoparticles. Gp120 protein was pretreated for 10 min with a two-fold serial dilution of silver nanoparticles, then added to a CD4-coated plate. The assay was done twice; the error bars indicate the s.e.m.