Human immunodeficiency virus (HIV)-induced cell fusion: quantification and its application for the simple and rapid screening of anti-HIV substances in vitro.

A coculture system using Molt-4 and its HIV-producing cell, Molt-4/HIV(HTLV-IIIB) induced syncytia very efficiently. Among the cocultivations with various ratios of two types of cells, multinucleated giant cells were most clearly visible 20 hr after culture in a cell ratio of 5:5. The degree of cell fusion apparently correlated with the decrease in cell number during fusion reaction. The grade of the syncytia formation can be quantitatively expressed by the fusion index (FI). Using this system we evaluated various substances which are known to inhibit HIV replication and virus-induced cytopathogenicity in a cell-free viral infection. Glycyrrhizin sulfate, dextran sulfate, PSK, which is a protein-bound polysaccharide extracted from Basidiomycetes, and human plasma containing anti-HIV antibody gave about 15-fold reduction in FI when compared to that of control. At the same time no difference was seen between the FI given by two nucleoside analogs (3'-azido-2',3'-dideoxythymidine and 2',3'-didehydro-2',3'-dideoxythymidine) and that of control.