Researchers find role for soft palate in adaptation of transmissible influenza viruses

NIH | OCTOBER 10, 2015

National Institutes of Health and Massachusetts Institute of Technology scientists identified a previously unappreciated role for the soft palate during research to better understand how influenza (flu) viruses acquire the ability to move efficiently between people.

Upper respiratory system. Credit: Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762./Wikipedia (CC BY 3.0)

Flu infection in mammals starts when an influenza virus protein called hemagglutinin binds to sialic acid (SA) molecules on the tops of chain-like proteins that thickly line tissue throughout the respiratory tract. Flu viruses adapted to humans and other mammals bind preferentially to a type of SA called alpha 2,6 SA (α2,6 SA), which is the predominant form found in the upper respiratory tract of mammals.

The researchers sequenced viral genetic material obtained from the ferret nasal washes. They discovered that airborne transmission was associated with a single genetic change in the engineered virus’s hemagglutinin that gave it the ability to bind to mammalian-type α2,6 SA of a particular class (long chain) without the loss of the other introduced changes that had made it a α2,3 SA binding type.

The soft palate, which has surfaces facing both the mouth and nasal cavity, stood out as the prime location for an abundance of virus containing the single genetic reversion that allows it to bind to mammalian-type SA. By three days post-infection, more than 90 percent of the viral material collected from the soft palate contained the reverted, long chain α2,6-binding form of virus.

Flu viruses with superior ability to transmit through the air are those that outcompete other flu virus variants in the soft palate and that inflammation associated with infection there stimulates the sneezing and coughing needed to better propel flu virus onward to new contacts.

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