Inhibition of HIV infection by CC-chemokines. Inhibition of viral entry by chemokines was assayed by infecting PM-1 cells with viruses pseudotyped with the env protein of the M-tropic HIV-1 strains ADA (▩) and BaL (□). Chemokines were used at a 1 μg/mL concentration, and the luciferase activity resulting from viral infection was measured. The data were normalized for basal luciferase activity (0%) and maximal activity in the absence of chemokines (100%). Each condition was run in triplicates, and the displayed results represent the mean of two independent experiments (error bars: S.E.M.).