Recent findings have generated renewed interest in so-called "non-neutralizing" antibodies that are unable to directly inhibit free virus entry into target cells, but nonetheless exhibit antiviral activity mediated by the Fc region of the antibody molecule. These antibody effector mechanisms include complement binding and viral lysis, phagocytosis of antibody-coated virions, and antibody-dependent cellular cytotoxicity [35] [36] [37] [38] . Recent studies have suggested examples of Fc-dependent antiviral effects of HIV-1-positive serum in cases where there was little or no detectable activity in conventional neutralization assays [39, 40] .