Macrophages bind directly to Semliki Forest virus-infected cells and mediate antibody-dependent cell-mediated cytotoxicity.

Macrophages were found to bind directly to Semliki Forest virus (SFV)-infected, but not uninfected, P815 cells. In the presence of anti-H-2d or anti-BALB/c antibody, macrophages lysed SFV-infected, but not uninfected, P815 cells. It is proposed that macrophage-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) proceeds via two functionally distinguishable initial steps: (1) adhesion of effector to target cell, which may be mediated through antibody or through viral protein, as in the case of SFV-infected target cells suboptimally sensitized with antibody; (2) antibody-dependent initiation of cytolysis.