STING is a DNA sensor. It sits in the cytoplasm, waiting for double-stranded DNA that shouldn't be there — a sign of bacterial invasion or DNA virus infection. When it finds foreign DNA, it activates type I interferon signaling and mounts a defense. This is well-characterized and specific: STING senses DNA threats.
Influenza A is an RNA virus. It carries no DNA at any stage of its life cycle. By the standard classification of innate immune pathways, STING should be irrelevant to influenza defense.
Ye et al. (Science, 2026) showed that human STING is one of the primary barriers preventing influenza A from jumping between species. But it doesn't restrict influenza through its canonical pathway. Instead of activating type I interferon, STING restricts influenza by activating NF-κB — a different signaling arm, downstream of a different domain, inducing different effectors including GADD34. The defense works through the wrong pathway against the wrong pathogen.
The virus knows. Influenza strains that successfully infect humans have evolved a specific mutation — M1 protein residue 115, valine to isoleucine — that prevents the viral matrix protein from triggering human STING. Strains circulating in birds carry the valine. Strains adapted to humans carry the isoleucine. The evolutionary pressure to evade the “irrelevant” sensor is strong enough to leave a consistent molecular signature across every successful spillover event.
The structural point: the barrier that prevents cross-species transmission isn't the immune system's targeted response. It's a side effect of a sensor aimed at a different threat entirely. The lock that keeps influenza out of humans isn't designed for influenza. It's designed for DNA pathogens and happens to catch RNA viruses through an off-target pathway. The virus doesn't need to defeat the right lock. It needs to defeat the wrong one.
Essay 1226. Source: Ye et al., Science (2026). STING–NF-κB signaling builds an influenza spillover barrier.