Viral release from HIV-I-induced syncytia of CD4+ C8166 cells.

Infection of the permissive C8166 CD4+ lymphoid cell line with human immunodeficiency virus (HIV)-I rapidly leads to syncytium formation. Ultrastructural features of medium-sized (40 to 60 microns) syncytia and larger syncytia are presented, with emphasis upon HIV-I release from the syncytial surface and into intrasyncytial vacuoles. Although surface release of HIV-I is shown to diminish with increasing syncytial size, it does not totally stop. Massive HIV-I release and entrapment within intrasyncytial vacuoles is clearly apparent within the "foamy" multivacuolated zones within medium and large syncytia. Numerous multicored aberrant viruses are routinely detected within the intrasyncytial vacuoles, and double-budding events likewise are readily detectable at the vacuolar membranes, but less so at the syncytial surface. It is suggested that this observation may be a reflection of the more restricted availability of vacuolar membrane area for excessive viral budding as compared with that at the syncytial surface.