Visualisation of phenotypically mixed HIV-1 and HTLV-I virus particles by electron microscopy.

Area of Science:

• Virology
• Immunology
• Cell Biology

Background:

• Human Immunodeficiency Virus type 1 (HIV-1) infection of cells transformed by Human T-lymphotropic virus type I (HTLV-I) results in virions with altered tropism.
• This tropism alteration has been hypothesized to be due to the incorporation of HTLV-I glycoproteins into the HIV-1 virion envelope.

Purpose of the Study:

• To directly identify and quantify phenotypically mixed virions resulting from HIV-1 infection of HTLV-I transformed cells.
• To investigate the mechanism of foreign envelope protein incorporation into HIV-1 particles.

Main Methods:

• Immunogold labeling electron microscopy was employed to visualize and identify virions containing both HIV-1 and HTLV-I components.
• Quantification of phenotypically mixed virions in cell-free supernatant was performed.

Main Results:

• Phenotypically mixed virions, characterized by the presence of HTLV-I glycoproteins in the HIV-1 envelope, were directly identified.
• Approximately 2% of cell-free virions were phenotypically mixed, reaching concentrations up to 1 x 10(7) particles/ml in vitro.
• HTLV-1 envelope protein labeling was localized to a specific region on the virion, suggesting a defined packaging event.

Conclusions:

• The study provides direct evidence for the existence of phenotypically mixed virions in HIV-1 infections of HTLV-I transformed cells.
• These mixed virions, containing HTLV-I envelope glycoproteins, contribute to the expanded tropism observed.
• The findings suggest a specific mechanism for the packaging of foreign envelope proteins into HIV-1 particles.