CD4 CONFERS SUSCEPTIBILITY TO HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INFECTION IN A RAT FIBROBLAST CELL-LINE

A new model system is delineated that mill enable study of CD4 cofacto rs and gp120 binding proteins other than CD4, We have previously descr ibed a nontransformed rat fibroblast cell line that can efficiently pr oduce HIV-1 upon transfection with an HIV-1 infectious clone, in contr ast to other nonhuman mammalian cell lines tested, In the present stud y we analyzed the susceptibility to HIV-1 infection of Rat2 cells expr essing the human CD4 protein, We have used the mammalian expression ve ctor pKS286, in which HIV-1 LTR drives the expression of the CD4 gene, We show that the Rat2 cell line, expressing the human CD4 (Rat2/CD4), is susceptible to fusion with and infection by HIV-1. The virus produ ced by the Rat2/CD4 cells was infectious, CD4 expression in the Rat2/C D4 was down-regulated over time, similarly to HIV-1 expression in HIV- 1-transfected Rat2 cells, Transfection of the Rat2/CD4 cells with a ta t expression vector reestablished the CD4 expression on the surface of those cells, as expected, We conclude that the expression of a gp120 binding protein on the Rat2 cells' surface suffices to render the Rat2 cells susceptible to HIV-1 infection.