Figure 5.

Antibodies to tetraspanins CD9 and -81 inhibit fusion by MPMV ^E . (A) Aliquots of MPMV^E were incubated with indicated antibodies, washed, and analyzed by immunoblotting (see Materials and methods). (B) Exosomes were treated with indicated antibodies and tested in the fusion assay with I0 or HepG2 cells, which express no CD81 (C). The experiments were done three times with I0 cells, except that total mouse IgG was used as a control only in two of these experiments, and the experiments with HepG2 cells were done twice. ND, not done. The error bars indicate SD. (C) CD81 is transferred to HepG2 cells by MPMV^E. HepG2 cells cultured for 22 h without (left) or with (right) MPMV^E from IE^H cells were probed with an antibody to CD81 (red). The nuclei were visualized with Hoechst 33342 (blue).