Focus formation by the human immunodeficiency virus (HIV) in the immobilized MT-4 cell culture and its application to the evaluation of anti-HIV agents

Abstract

Immunofluorescence studies were performed on the infection of monolayer cultures of immobilized MT-4 cells with human immunodeficiency virus type 1 (HIV-1). By using the anti-viral p24 monoclonal antibody, we could observe formation of foci of p24 antigen-positive cells within 3 to 4 days when the infection was initiated with a relatively small amount of the virus. Frequency of the focus formation was in proportion to the dose of input virus (ranging from 0.001 to 0.1 PFU/cell), which allowed us to apply this phenomenon to the assay of anti-HIV agents as well as to the estimation of relative infectivity of the virus stocks. When antiviral agents were added to the infected cultures, number of foci as well as the size of each focus was reduced in a concentration-dependent manner. The dose required for reducing the number of foci by 50% was calculated to be 6 ng/ml and 8 ng/ml for tunicamycin (TM) and azidothymidine (AZT), respectively. These values are comparable to those obtained by other current assay methods. In addition, focus reduction assay is also useful in searching for such antiviral agents that would inhibit or block the early step of viral replication cycle.