DEVELOPMENT OF A FLOW CYTOMETRIC ASSAY FOR THE DETECTION AND MEASUREMENT OF NEUTRALIZING ANTIBODIES AGAINST HUMAN-IMMUNODEFICIENCY-VIRUS

Cells infected with human immunodeficiency virus type 1 (HIV-1) develop viral antigens which can be detected by immunofluorescence. We developed a flow cytometric immunofluorescence assay (FIFA) which provides a quantitative analysis of HIV-1 p24 using a monoclonal antibody (mAb) as aspecific reagent. The reduction of HIV p24 antigen expression in viral infected cells was then used to determine HIV neutralizing antibody titers in human sera. Results obtained by FIFA for detecting neutralizing antibodies against HIV-I, when compared with results obtained by indirect immunofluorescence assay (IFA), showed an overall index of agreement of 94.1%. The correlation between the neutralizing antibody titers obtained with each method was found to be highly significant (ro=0.8; p<0.01). The simple methodology and the adaptability of this FIFA to various assay conditions make it suitable for routine purposes and for assessing the efficacy of vaccination strategies.