Isolation of a retrovirus from cultured equine sarcoid tumor cells.

This research reports the isolation of a virus with similar properties to the family Retroviridae from the cultured cells of a malignant tumor, which was formed from the injection of equine sarcoid cells into a foal with a depleted immune system. This virus incorporates uridine instead of thymidine and exhibits an optimal endogenous activity in the presence of Mn2+.

Study Overview

• The research focuses on the isolation and identification of a certain virus from the malignant tumor cells of a combined immunodeficient Arabian foal (a young horse).
• The malignant tumor in the foal was induced by the introduction of equine sarcoid cells into the skin.
• The extracted virus shares morphologic and biochemical properties with the family Retroviridae, a family of enveloped viruses that replicate in a host cell through the process of reverse transcription.

Key Findings

• Virus particles were observed within the cytoplasm of the cells, outside the cells, and in the process of budding from the cell surface. These particles ranged in size from 89 to 120 nanometers and contained electron-lucent cores, observable under electron microscopy.
• These virus particles were successfully purified from the medium of cultured cells indicating the successful cultivation of the virus in a lab environment.
• Measured buoyant density of the purified virus in an isopycnic sucrose-gradient centrifugation was 1.15 g/cm³, which is consistent with other retroviruses.

Nucleic Acid Metabolism of the Virus

• This isolated virus incorporated radiolabeled uridine, not thymidine. The ability to incorporate uridine is a feature of certain RNA viruses, suggesting this may be an RNA virus.
• The virus was found to have an inherent RNA-dependent DNA polymerase activity – a characteristic of retroviruses that allows them to reverse-transcribe their RNA genome into DNA after they infect a cell.
• This RNA-dependent DNA polymerase activity required the presence of Mn2+ ions for optimal endogenous activity. This is a key observation as some viruses require specific ions to optimally carry out their enzymatic activities.