Red blood cells bearing CD4 bind to gp120 covered plates and aggregate with cells expressing gp120.

Full-length recombinant CD4 (rCD4) was bound to human red blood cell membranes using a low-pH incubation procedure. The red blood cells bearing recombinant CD4 (RBC-rCD4+) specifically bound to gp 120-covered plates. The binding showed a threshold effect at low rCD4 concentrations per RBC. The binding of RBC-rCD4+ to gp120 plates was not inhibited by plasma proteins (incubation in human blood plasma). Preincubation of the RBC-rCD4+ with monoclonal anti-CD4 antibodies blocked the binding to the gp120-covered plates. Incubation of chinese hamster ovary (CHO) fibroblasts, which constitutively express the HIV envelope protein gp120 with RBC-rCD4+, resulted in the formation of large cell aggregates. These in vitro data suggest that RBC-rCD4+ retain affinity for gp120 and thus could have potential therapeutical value in AIDS treatment.