FIG. 3.

(A) Correlation between coreceptor usage profiles and fusion specificities for natural target cells. For each Env, the ratio of the fusion activity with CCR5 versus CXCR4 was calculated from the data shown in Fig. 2 (open triangles); the ratio of the relative fusion activity obtained with macrophage versus Jurkat cell targets was calculated from the data in Table 1 (closed circles). All ratio values below 0.1 or above 10 were grouped together. (B) Functional CXCR4 coreceptor on macrophages. Macrophages coinfected with vTF7-3 (T7 RNA polymerase) and vCB-3 (CD4) were preincubated for 45 min at 37°C without antibody or with 1 mg of preimmune or immune immunoglobulin per ml purified from a rabbit immunized with a peptide representing the extracellular N terminus of CXCR4 (24). Effector HeLa cells were coinfected with vCB21RLacZ and either vCB-41 (LAV Env), vCB-43 (Ba-L Env), or vCB-16 (Unc Env). The Ba-L Env infection was performed with AraC to reduce the fusion activity so that it was comparable to that of the LAV Env; similar results were obtained when the Ba-L Env was expressed without AraC (i.e., no inhibition; data not shown). For the LAV and Ba-L Envs, the minimal values obtained with Unc Env were subtracted and the results are expressed as the percentage of activity obtained in the absence of antibody (set at 100%). Error bars indicate the sample standard deviations of the mean values obtained from duplicate samples.