Standardized microtiter assay for determination of syncytium-inducing phenotypes of clinical human immunodeficiency virus type 1 isolates

A standardized assay in 96-well microtiter plates for syncytium-inducing (SI) human immunodeficiency virus type 1 phenotype detection using MT-2 cells has been developed. SI variants were found in 67 % of the patients with advanced human immunodeficiency virus disease. The occurrence of the SI phenotype increased with lower CD4+ counts. There was no association between p24 antigenemia and the SI phenotype. Syncytium-inducing (SI) human immunodeficiency virus type 1 (HIV-1) variants have been shown to be clinically significant in the pathogenesis of HIV-1 infection (1-3, 10, 12, 18). The ability of HIV-1 isolates to produce cytopathic effects in a human T-cell leukemia virus type I-transformed lympho-blastoid cell line (MT-2 cells) has been shown to be sensitive to and specific for SI capacity (5, 11). Within a single HIV-positive individual, a heterogenous population of SI and non-SI (NSI) HIV-1 can be detected, and these virus popula-tions shift over time (4, 13). A shift from a predominately monocytotropic NSI HIV-1 variant population to a T-cel