Transcriptome analysis reveals strong and complex antiviral response in a mollusc

Area of Science:

• Marine biology
• Innate immunity
• Virology

Background:

• Filter-feeding molluscs lack adaptive immunity, making their antiviral defense mechanisms poorly understood.
• Ostreid herpesvirus 1 µVar (OsHV-1μVar) causes significant mortality in oysters.

Purpose of the Study:

• To investigate the antiviral immune response of the oyster Crassostrea gigas to OsHV-1μVar infection.
• To understand how molluscs without adaptive immunity defend against viral threats.

Main Methods:

• Transcriptome sequencing of Crassostrea gigas post-OsHV-1μVar challenge.
• Analysis of viral replication markers (transcription, DNA synthesis) and host gene expression.
• Monitoring of oyster mortality rates.

Main Results:

• Rapid OsHV-1μVar replication and high oyster mortality observed initially.
• Surviving oysters showed reduced viral load and mortality, indicating effective viral control.
• Oysters activated diverse innate immune pathways, including novel Toll-like receptor (TLR) and MyD88-like genes.
• Upregulation of RIG-1/MDA5, interferon-regulatory factors, and interleukins indicated a strong antiviral response.
• Oxidative burst potentially aids viral destruction but may also contribute to mortality.

Conclusions:

• Crassostrea gigas employs a complex innate immune strategy to combat viral infections.
• Expanded and novel immune gene families in oysters reflect adaptation to virus-rich marine environments.
• The balance between viral destruction and host damage via oxidative stress is crucial.