Quantitative analysis of syncytium-inducing and non-syncytium-inducing virus in patients infected with human immunodeficiency virus type 1.

Among 75 consecutive human immunodeficiency virus type 1 (HIV-1)-infected patients with moderate and advanced immunosuppression, those harboring syncytium-inducing (SI) HIV-1 had a lower CD(4+)-cell count (145 versus 278 cells per microliter, P < 0.001) and 10-fold-higher virus titers than patients with non-SI HIV-1 (398 versus 39 infectious units per 10(6) CD4+ lymphocytes; P < 0.001). In patients with SI virus, the mean titer of SI virus, determined with a quantitative MT-2 cell assay, was 135 SI infectious units per 10(6) CD4+ lymphocytes. Virus titer correlated inversely with CD(4+)-cell count in patients with SI (r = -0.67) but not non-SI (r = -0.29) virus.