Immunofluorescence analysis of HeLa cells transiently transfected with expression vectors for HERV-W Env proteins. HeLa cells were transfected for 24 hours with the indicated expression vectors. Xq22.3 Env rev is a control plasmid which contains the Xq22.3 Env sequence in reverse orientation. Immunocytochemistry was performed on fixed and permeabilized cells with mAbs 13H5A5 and 6A2B2, as well as an anti-Syncytin-1 pAb. Cell nuclei were stained with 4',6'-diamidino-2-phenylindole (DAPI). Magnification × 160.