Decoy receptors and cytokine sponges
A decoy receptor is a viral protein that binds a host cytokine or chemokine with high affinity but lacks the signaling domain of the real receptor. It acts as a sink, reducing the effective concentration of the effector before it can reach its target cell. Poxviruses encode soluble interleukin-18 binding proteins and tumor necrosis factor receptor homologs that work this way. The same logic applies inside the cell when a viral protein binds STAT1 or triggers its degradation: the cell becomes unresponsive to interferon even though interferon is present in the tissue.
Latency as the deepest form of hiding
Latency removes the infected cell from immune surveillance by shutting down viral gene expression almost completely. Herpes simplex virus establishes latency in sensory neurons, where MHC class I expression is low and immune access is limited, and the viral genome persists as an episome. Reactivation briefly re-enters the lytic cycle, produces new virions, and can retreat to latency again. The virus must maintain the episome and reactivation machinery for the lifetime of the host, but during the latent phase the immune system has almost no viral protein to target.
How each strategy buys time
Decoy receptor
- Neutralizes a cytokine or chemokine before it reaches its receptor
- Acts in the extracellular space
- Reduces the effective concentration of one effector at a time
Cytokine antagonism inside the cell
- Blocks STAT1 or other signaling nodes
- Makes the cell deaf to interferon even when interferon is present
- Disables the response rather than the ligand
Latency
- Shuts down viral gene expression almost completely
- Removes the infected cell from immune surveillance
- Requires maintenance of the episome and reactivation machinery