FIG. 2.

Sensitivity to soluble CD4, SDF-1α and HIVIG. The U87-CD4-CXCR4 cell microculture virus inhibition assay is described in the text (26). Inhibition is indicated as the percent reduction in the number of infected-cell foci relative to the control virus input. (A) The sCD4 ectodomain was obtained from Progenics Pharmaceuticals, and (B) the CXCR4 chemokine SDF-1α was kindly provided by Ian Clark-Lewis (University of British Columbia). (C) HIVIG, an immunoglobulin preparation from HIV-infected persons, was provided by Fred Prince (New York City Blood Center). In each case, the results of a representative study performed in duplicate are shown; replicate experiments yielded concordant results. Wild type (circle) and fusion-intact mutants Q551A (square) and Q563A (diamond) are shown as open symbols. Fusion-deficient mutants L556A (square), L565A (circle), and V570A (diamond) are shown as closed symbols.