Interaction between the human T-cell lymphotropic virus type IIIB envelope glycoprotein gp120 and the surface antigen CD4: role of carbohydrate in binding and cell fusion.

Interactions between retroviruses associated with acquired immunodeficiency syndrome and their receptors on lymphocytes represent the initial steps in the process of infection and are also involved in multinucleated giant cell formation, which is one form of virus-mediated cytopathology. The exterior envelope glycoprotein of the retrovirus has been identified as gp120, and we demonstrate here that purified gp120 binds directly to cells expressing the CD4 (T4) surface antigen at a site spatially related to that recognized by the OKT4A monoclonal antibody. The gp120 was also able to temporarily interfere with viral infection and to block the process of multinucleated giant cell formation. However, if the carbohydrate chains were removed from gp120 by enzymatic treatment, CD4 binding and blockade of cell fusion was reduced by about a factor of 50. The significance of these results in relation to preventive and interventive approaches for acquired immunodeficiency syndrome is discussed.