BINDING OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TO THE C3B C4B RECEPTOR CR-1 (CD35) AND RED-BLOOD-CELLS IN THE PRESENCE OF ENVELOPE-SPECIFICANTIBODIES AND COMPLEMENT/

Immune complexes formed in vitro by incubating cell-free human immunod eficiency virus type 1 (HIV-1) with sera from infected or gp160-vaccin ated persons, together with normal human serum as a source of compleme nt, readily bound to K562 cells expressing recombinant human complemen t receptor type 1 (CR1). However, antibodies from seronegative persons had little or no effect. This effect was absent in the presence of he at-inactivated or C3-depleted normal human sera or when wild type K562 cells were used, confirming a requirement for complement and CR1. In additional experiments, complement alone targeted HIV-1 to CR1 on red blood cells, and envelope-specific antibodies increased this effect. T hese results demonstrate that envelope-specific antibodies promote HIV -1 immune complex formation with complement and that these complexes r eadily bind CR1 on cell surfaces.