Maturation of human immunodeficiency virus, strain LAV, in vitro.

The budding process of human immunodeficiency virus (HIV), strain LAV, starts with the formation of a crescent electron-dense layer directly underneath the cell membrane of infected CCRF-CEM cells. After completion of the formation of the circle of inner dense layer, immature virions with an electron-lucent center are released from the cells. Serial thin sections and stereo observation of thick sections showed that most of the immature virions adjacent to the cell surface had already come off the cell and some still had very thin connections to the cell. However, on rare occasions, virions at an intermediate stage between immature stage and mature virions with bar-shaped electron-dense cores were observed. Virions with dense cores were never observed to be connected to the cell surface. These observations support the idea that the last step of the maturation of HIV occurs outside the cell and that the electron-dense core seems to develop by rearrangement and dispersion of the substance of the inner dense layer of immature virions.