Enhancement of NK cell-mediated antibody-dependent lysis of recombinant gp120-coated CD4 cells by complement

The contribution of complement to NK cell lysis of CD4 cells expressing recombinant gp120 (rgp120) was investigated. Peripheral blood mononuclear cells were used as effector cells in a Cr release assay against purified CD4 target cells that had been coated with rgp120. Assays included human immunodeficiency virus (HIV) antibodies and a complement source alone and in combination to determine their importance in mediating cytotoxicity. NK cells were confirmed to be the effector cells in the lysis of rgp120-coated CD4 targets. Anti-HIV was crucial for lysis and cytotoxicity was enhanced by C3 deposition on targets. However, a prozone effect was observed, with reduced IgG binding, C3 deposition, and NK cell lysis at serum concentrations > 10 micrograms IgG/mL. The susceptibility of these CD4-gp120-antibody-C3 complexes to NK cell lysis may contribute to progressive depletion of CD4 cells in HIV infection.