Early syncytium formation by bovine leukemia virus

Area of Science:

• Virology
• Cell Biology
• Immunology

Background:

• Bovine leukemia virus (BLV) is a significant pathogen in cattle, causing persistent lymphocytosis and leukemia.
• BLV is known to induce syncytium formation, a process involving cell fusion, in various cell types.
• Understanding the mechanisms of BLV-induced cell fusion is crucial for developing control strategies.

Purpose of the Study:

• To investigate the kinetics and requirements of BLV-induced syncytium formation in F81 indicator cells.
• To determine if BLV replication is necessary for early syncytium formation.
• To assess the role of specific BLV proteins and cellular synthesis pathways in the fusion process.

Main Methods:

• Inoculation of F81 cells with cell-free BLV preparations from infected bat or lamb kidney cells.
• Observation of syncytium formation over time at varying BLV concentrations and cell densities.
• Inhibition assays using BLV-specific antisera (anti-gp51, anti-p24), control sera, beta-propiolactone, and UV irradiation.
• Assessment of BLV replication via p24 expression and evaluation of cellular synthesis inhibitors (cycloheximide, cytosine arabinoside, tunicamycin, 2-deoxy-D-glucose).

Main Results:

• Rapid syncytium formation occurred within 2-8 hours post-inoculation, with optimal indicator cell densities identified.
• BLV-specific antisera, particularly anti-gp51, significantly inhibited syncytium formation (up to 96%), while control sera had minimal effect.
• Beta-propiolactone and UV irradiation reduced fusion activity but drastically impaired BLV replication; inhibitors of cellular macromolecular synthesis did not inhibit early syncytium formation.

Conclusions:

• Early syncytium formation induced by BLV is a rapid process that does not depend on de novo viral replication or cellular macromolecular synthesis.
• The BLV envelope glycoprotein gp51 plays a critical role in mediating BLV-induced cell fusion.
• These findings suggest that BLV cell fusion is an early event mediated by viral components, independent of productive viral replication within the indicator cells.