Human T-lymphotropic virus-1 visualized at the virological synapse by electron tomography

Area of Science:

• Virology
• Cell Biology
• Immunology

Background:

• Human T-lymphotropic virus 1 (HTLV-1) transmission occurs via cell-cell contact (virological synapse, VS).
• The ultrastructure of the HTLV-1 VS and the nature of transmitted viral particles were previously unknown.
• Cell-free HTLV-1 virions are undetectable, yet viral envelope protein is crucial for infectivity, suggesting direct particle transfer.

Purpose of the Study:

• To elucidate the ultrastructure of the HTLV-1 virological synapse.
• To determine the nature of HTLV-1 particles transmitted during cell-cell contact.
• To visualize the direct cell-to-cell transmission mechanism of HTLV-1.

Main Methods:

• Utilized electron tomography combined with immunostaining for viral proteins.
• Analyzed virological synapses formed between naturally HTLV-1 infected lymphocytes.
• Reconstructed 3D images to visualize viral particle location and interaction within the VS.

Main Results:

• Demonstrated the presence of enveloped HTLV-1 particles within the virological synapse.
• Showed HTLV-1 particles within multiple synaptic clefts simultaneously in 3D.
• Observed HTLV-1 virions contacting the recipient cell membrane before detachment.

Conclusions:

• The HTLV-1 virological synapse facilitates direct cell-to-cell transmission of enveloped viral particles.
• Transmission involves triggered, directional release of HTLV-1 into confined intercellular spaces.
• This mechanism explains the infectivity of HTLV-1 despite the absence of cell-free virions.