The ratio of defective HIV-1 particles to replication-competent infectious virions

The ratio of infectious to defective particles has been investigated for human immunodeficiency virus type 1 (HIV-1). Although the concentration of HIV core p24 protein defined by ELISA permits the estimation of a total number of average-sized HIV particles, it does not provide information on the numerical value of infectious particles. This problem was addressed by limiting dilution of viral supernatant derived from various infected cell lines and then comparing the total number of HIV particles to the end-point titers of viral inoculum determined by reverse transcriptase assay and virus-induced cytotoxicity. The results indicate that the ratio of infectious to defective virus particles varies for different virus strains and host cells within a range from 1:1 to 1:100, but for given virus-cell system it remains constant.