A specific assay measuring binding of 125I-Gp 120 from HIV to T4+/CD4+ cells.

The HIV (HTLV-III) envelope glycoprotein, Gp120, was isolated from virus-infected tissue culture cells using affinity chromatography. A radioimmunoassay was developed to determine the degree of iodinated Gp120 to target CD4+ (T4+) cells. 125I-Gp120 could be shown to selectively bind to CD4+ cells only. The Gp120 remained bound to these cells after repeated washes. Monoclonal anti-CD4 antibodies block the binding of Gp120 to CD4+ cells. Monoclonal antibodies to other cell surface components do not interfere with 125I-Gp120 binding. All IgG antibodies from HIV seropositive donors tested block 125I-Gp120 binding, though with variable titers. We believe that this assay provides further proof for the use of CD4 (T4) as a component of the receptor for HIV. It represents a safe, objective and sensitive method for the analysis of Gp120-CD4 interactions, as well as the potential of antibodies to interfere with this binding.