[Receptor sialylsugar chains as determinants of host range of influenza viruses].

The research explores how influenza A viruses, found in humans, pigs, horses, and aquatic birds, identify and bind to specific sugar chains on cell receptors based on the presence of different forms of sialic acid, which influences the range of hosts the virus can infect.

Understanding Virus Attack Mechanisms

• The hemagglutinin (HA) found in influenza A viruses from diverse host species, recognizes specific sugar chains, known as sialyl lacto-series type I and II, in the target cells’ glycoproteins and glycolipids. This recognition serves as a common receptor molecule allowing the virus to infect different organisms.
• The study points out that the distribution of sialic acid (SA) variations in different animal species can steer the host range that an influenza virus strain can infect.

Specificity of Virus Binding

• The nature of binding is determined by the specificity of the virus for different SA linkages. Avian and equine influenza viruses preferentially bind to SA2-3Gal linkage, whereas human influenza viruses are attracted to the SA2-6Gal linkage.
• The variety of receptors sets the proficiency of the virus to infect different hosts. As an example, swine trachea carries both receptors – for avian influenza viruses (SA2-3Gal specific) and for human influenza viruses (SA2-6Gal specific).

Implications for Viral Replication

• In horses, an HA virus that recognizes Neu5Ac2-6Gal failed to replicate, implying that such a receptor binding site does not favor viral proliferation. However, another virus-HA that could recognize Neu5Gc2-3Gal was able to replicate, suggesting that this molecular interaction is pivotal for viral replication in horses.
• The high prevalence of Neu5Gc2-3Gal in horse trachea epithelial cells lends support to this observation.

Sialic Acid Species and Viral Replication

• Moreover, Neu5Gc2-3Gal also plays a role in viral replication in the duck intestine, primarily in the crypt epithelial cells. The ability of a virus to replicate in the duck’s colon coincided with the presence of Neu5Gc in crypt cells.
• These findings underscore the biological effect of different sialic acid species in different animals, not only defining host range of influenza viruses but also influencing the virus’s ability to replicate within the host.