The PD-1/PD-L1 Axis and Virus Infections: A Delicate Balance

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• Programmed cell death protein 1 (PD-1) and its ligands (PD-L1, PD-L2) are key regulators of immune responses.
• The PD-1/PD-L1 axis is known for its role in tumor immune evasion.
• Emerging evidence highlights its significant role in modulating antiviral immunity.

Purpose of the Study:

• To review the intricate interplay between viruses and the PD-1/PD-L1 axis.
• To discuss the dual role of PD-1/PD-L1 in viral infections, including immune regulation and evasion.

Main Methods:

• Literature review of studies investigating the PD-1/PD-L1 axis in viral infections.
• Analysis of experimental evidence on PD-1/PD-L1 expression and function during viral pathogenesis.

Main Results:

• PD-1 and its ligands are upregulated during acute and chronic viral infections, including HIV, HCV, and HBV.
• Insufficient PD-1 signaling can exacerbate immunopathology in acute infections.
• High PD-1 expression in chronic infections can lead to immune exhaustion, suppression, and viral evasion.
• PD-L1 may also exert inflammatory effects during the acute phase of immune responses.

Conclusions:

• The PD-1/PD-L1 axis plays a complex and multifaceted role in antiviral immunity.
• Understanding this axis is crucial for developing strategies against viral infections and associated immune dysregulation.