ISG
Interferon-stimulated genes; the molecular first-line alarm of innate immunity that B3.13 H5N1 partially suppresses.
Last refreshed: 12 May 2026 · Appears in 1 active topic
If B3.13 suppresses ISGs in human nasal cells, how much more time does that give the virus before the immune system responds?
Timeline for ISG
Suppressed below the level induced by historical H5N1 strains when B3.13 was present in nasal epithelium cultures
Pandemics and Biosecurity: B3.13 replicates better in human nasal tissueMentioned in: USDA ends mandatory H5N1 interstate cattle tests
Pandemics and Biosecurity- What are interferon-stimulated genes and why do they matter for flu?
- ISGs are activated by interferon to produce antiviral proteins that slow viral replication before the adaptive immune system engages. Influenza strains that suppress ISGs gain a replication advantage in the early infection window.
- How does B3.13 H5N1 evade the immune system?
- A May 2026 NIH/NIAID study found B3.13 suppresses interferon-stimulated gene responses in human nasal epithelium cultures more effectively than historical H5N1 strains, delaying the innate immune alarm.Source: CDC Emerging Infectious Diseases
- Why does ISG suppression increase pandemic risk for a new influenza strain?
- Suppressing ISGs delays the innate immune alarm, giving the virus more time to replicate and potentially spread before the host mounts an effective response — a key virulence characteristic in pandemic strains.Source: CDC Emerging Infectious Diseases
Background
Interferon-stimulated genes (ISGs) are the suite of genes activated when a cell detects viral infection and releases interferon signalling proteins. The interferon response is the body's fastest molecular alarm: infected cells broadcast interferon, neighbouring cells upregulate ISGs, and a cascade of antiviral proteins and immune-cell recruiters halts viral spread before the slower adaptive immune system (T-cells, antibodies) can engage. ISGs include well-characterised antiviral effectors such as MX1, OAS1, and IFITM proteins, each of which disrupts viral replication, entry, or translation at the cellular level.
ISG suppression is the mechanism by which many successful respiratory viruses — including SARS-CoV-2, influenza A, and now B3.13 H5N1 — buy time inside the host before the immune system mounts a co-ordinated response. A pathogen that suppresses ISGs is not invisible to the immune system indefinitely; it is delaying the alarm, not disabling it. The window of delay determines how FAR the virus can spread within a host and how infectious the early disease period is.
The May 2026 CDC Emerging Infectious Diseases study on B3.13 (DOI: 10.3201/eid3205.260053) found that the genotype suppresses ISG responses in human nasal epithelium cultures more effectively than historical H5N1 strains. Combined with B3.13's improved nasal replication, this shifts the mechanistic picture: the virus can reach the primary infection site and delay the molecular alarm, giving it more time to replicate before immune clearance begins. ISG suppression does not determine pandemic outcome alone — transmission mode, receptor binding, and population immunity all matter — but it is a key virulence determinant that distinguishes B3.13 from earlier H5N1 strains.
