The BeWo-CD4+ cell line expresses CD4 capable of binding HIV-1 gp120 recombinant protein. A) Expression of the CD4 surface molecule on the cell membrane of a selected BeWo cell line. The CD4 antibody used recognises the gp120 binding domain of CD4. The left panel shows wild type BeWo cells stained with anti-CD4 antibody; the right panel shows staining of the CD4+ BeWo cell line. B) gp120-CD4 binding assays on the CD4+ BeWo cell line. The CD4+ cell line was incubated with increasing concentrations of recombinant gp120 protein and subsequently stained with an anti-gp120 antibody, followed by a FITC-conjugated secondary antibody; cells were analysed by flow cytometry. The gp120 recombinant protein is derived from a BaL HIV-1 strain.