Ultrastructural studies on Maedi-Visna virus

The life-cycle of human immunodeficiency virus type 1

The life-cycle of human immunodeficiency virus type 1 (HIV-1) has been studied using several techniques including immunoelectron microscopy and cryomicroscopy. The HIV-1 particle consists of an envelope, a core and the region between the core and the envelope (matrix). Virus particles in the extracellular space are observed as having various profiles: a central or an eccentric round electron-dense core, a bar-shaped electron-dense core, and immature doughnut-shaped particle. HIV-1 particles in the hydrated state were observed by high-resolution electron cryomicroscopy to be spherical and the lipid membrane was clearly resolved as a bilayer. Projections around the circumference were seen to be knob-like. The shapes and sizes of the projections, especially the head parts, were found to vary with each projection. HIV-1 cores were isolated with a mixture of Nonidet P40 and glutaraldehyde, and were confirmed to consist of HIV-1 Gag p24 protein by immunogold labelling. On infection, the HIV-1 virus was found to enter the cell in two ways: membrane fusion and endocytosis. After viral entry, no structures resembling virus particles could be seen in the cytoplasm. In the infected cells, positive reactions by immunolabelling suggest that HIV-1 Gag is produced in membrane-bound structures and transported to the cell surface by the cytoskeletons. A crescent electron-dense layer is then formed underneath the cell membrane. Finally, the virus particle is released from the cell surface and found extracellularly to be a complete virus particle with an electron-dense core. However, several cell clones producing defective mature, doughnut-shaped (immature) or teardrop-shaped particles were found to be produced in the extracellular space. In the doughnut-shaped particles, Gag p17 and p24 proteins exist facing each other against an inner electron-dense ring, suggesting that the inner ring consists of a precursor Gag protein showing a defect at the viral proteinase.

The morphology of human immunodeficiency virus (HIV) by negative staining

We have examined preparations of human immunodeficiency virus 1 (HIV-1) and HIV-2 by negative staining electron microscopy. HIV-2 cultures contained large numbers of 130-200 nm particles containing a 130-nm-long by 30-70 nm-wide core. This core is probably of conical or pear-shaped morphology. Some particles exhibited a short fringe that could be seen to comprise a regular arrangement of repeating subunits when visualised end on. Identical particles were found in HIV-1 cultures but in much lower numbers. Attempts to carry out negative staining immune EM were unsuccessful. Also detected in both HIV-1 and HIV-2 cultures were small (70-80 nm) fringed viruslike particles. The possible significance of these particles is discussed.

Budding process and fine structure of lymphadenopathy-associated virus (LAV)

The budding process and fine structure of lymphadenopathy-associated virus (LAV), were studied by indirect immunofluorescence (IF) and electron microscopy (EM). By IF, LAV antigen was seen to be distributed focally within infected CCRF-CEM cells. Consistent with this finding, electron micrographs showed that LAV particles occurred in a focally aggregated state in a restricted area of the surface of the infected cells. LAV particles possessed bar-shaped, dense and central or eccentric cores. In addition, two or more cores were occasionally observed in one virus particle, or the cores were sometimes absent when thin sections were examined. The envelope of the virus particles had an irregular structure, although LAV particles were approximately spherical.

Morphology and immunoelectron microscopy of AIDS virus

Lymphocytes infected with human T-lymphotropic virus type III/lymphadenopathy-associated virus were examined by thin-section and immunoelectron microscopy, with horseradish peroxidase as an electron-dense marker. There was no evidence of an intracytoplasmic virion precursor, but viral antigen accumulated at the plasma membrane. Particles formed at the plasma membrane, and most virus was found in extracellular spaces. Mature virus had an envelope with fuzzy surface projections surrounding a centric core and an electron-dense eccentric nucleoid.