Plaque staining assay for non- or weakly cytotoxic human immunodeficiency virus

Cells infected with human immunodeficiency virus (HIV) were selectively stained with peroxidase-coupled antibodies in a recently developed plaque assay for HIV. The numbers of plaques formed with the human T-cell lymphotropic virus type III strain of HIV were exactly the same in stained (immunologically detectable) and unstained (visible) dishes. However, four times more plaques were visualized in stained dishes than in unstained dishes when the YU-6 and acquired immune deficiency syndrome-associated retrovirus strains of HIV were used. Linear relationship was observed between the number of stained plaques and the virus concentrations in the titration of human T-cell lymphotropic virus type III and YU-6. The assay should be useful for the titration of HIV, especially for non- or weakly cytopathic strains of HIV.