Cytopathic effect determined by the amount of CD4 molecules in human cell lines expressing envelope glycoprotein of...

A plasmid which has an envelope gene from the human T lymphotropic virus IIIB isolate of HIV under the transcriptional control of the human metallothionein IIA promoter was constructed and transfected into human CD4+ and CD4- cell lines. When the expression of the env gene was induced with metal ions in cloned cell lines from such transfected cells, the viral envelope protein precursor, gp160, was produced in both the CD4+ and CD4- cell clones in the same amounts. An extensive cytopathic effect developed resulting in cell killing; however, this occurred only in CD4+ and not in CD4- cell clones. The formation of syncytium was not found in those cells showing cytopathic effect. Immunofluorescence microscopy showed the envelope proteins localized in the periphery, forming a mass in the CD4+ cells but not in the CD4- cells after induction. Moreover, immunoprecipitation and immunoblot analyses demonstrated the formation of a complex between gp160 and CD4 molecules in the cytoplasm of those cells from whose surface CD4 Ag had already disappeared. Therefore, it is proposed that the formation of such a complex is directly related to the cell killing of CD4+ cells by envelope proteins in our cell clones as well as in infections with HIV.