Figure 4

Cell adhesion by vector particles. Panel A: HIV particles without CD4, or carrying CD4 or one of the different chimeric CD4 proteins in their envelope, were generated by cotransfections with pHDPack1 in HeLa cells. Equal numbers (10 ng p24) of particles were adsorbed in suspension for 30 min at 4°C to 10⁵ Env⁺ or Env^- target cells (HeLa or CHO). The amount of adsorbed virus particles associated with the cell pellet was determined by p24 ELISA. Panel B: Time course of cell adhesion by HIV particles. Binding of HIV(CD4) particles to Env⁺ cells (□), Env^- cells (●), or adhesion of HIV(w/o CD4) particles to Env⁺ cells (△). Adsorption was normalized to the maximal amount of CD4⁺ particles adsorbed to HIV Env⁺ cells at 30 min (= 100). Contributions of the CD4-dependent, and the Env-dependent cell adhesion are indicated. Panel C: Inhibition of virus binding by either anti-CD4 antibody (left panel) or soluble CD4 (right panel). Equal p24 amounts of HIV(CD4) particles were adsorbed to either Env⁺ (□) or Env^- (△) HeLa cells. The amounts of bound vectors were compared to the adsorption of HIV(w/o CD4) particles to Env⁺ cells (△). Before cell adsorption, the vector particles were preincubated with increasing amounts of polyclonal antibody to CD4. Alternatively, with sCD4, the target cells were preincubated before addition of the vector particles.