UPTAKE OF HUMAN-IMMUNODEFICIENCY-VIRUS ENVELOPE PROTEIN GP120 BY HUMAN TROPHOBLAST IN CULTURE

OBJECTIVE: Our purpose was to determine whether human trophoblast has a cell surface CD4 antigen that will bind to gp120, the envelope prote in of human immunodeficiency virus. STUDY DESIGN: Uptake of iodine 125 -labeled gp120 by trophoblast in culture was measured. Particular atte ntion was paid to technical details that may have caused the contradic tory results reported by previous investigators: the source of the rec ombinant gp120, the method of radioiodination, and the isolation proce dure of trophoblast to ensure elimination of contaminating cells, part icularly macrophages. RESULTS: Uptake of transferrin-free iodine 125-l abeled gp120 to trophoblast was unaffected by adding a 200 molar exces s of gp120, by preincubating gp120 with soluble CD4 to block the CD4 b inding sites on gp120 and by preincubation of trophoblast with a block ing antibody to CD4 (OKT4a). In contrast, uptake of gp120 by CD4-posit ive H9 human lymphocytes was reduced 79% by a 200 molar excess of gp12 0 and >50% by a CD4-blocking antibody. CONCLUSIONS: Uptake of gp120 to trophoblast is by a high capacity, CD4-independent mechanism that is probably nonspecific and may be related to the mechanism for binding o ther circulating glycoproteins in maternal blood.