Researchers have found that the influenza viruses don’t prefer a particular type of sugar structure in pig lungs. Image from http://en.wikipedia.org/wiki/File:Pig_in_a_bucket.jpg
Just like birds, pigs can harbor influenza viruses that can jump to humans and cause public-health emergencies, like the H1N1 global pandemic of 2009 . To understand how viruses interact with their hosts and develop better vaccines against them, researchers want to know what molecules viruses bind to on their hosts’ cell surfaces.
In a paper just out in the Proceedings of the National Academy of Science, researchers demonstrate that the individual influenza viruses have their own particular preferences for the sugars they bind to on the lung cells of the pig. There isn’t a common motif that all viruses recognize. The research could better inform vaccine development.
Richard Cummings and David Steinhauer at Emory University led a team to check out the sugar molecules that cover cell surfaces. These sugar molecules are known to be essential for the virus-host interaction.
The researchers had earlier studied sugar chains, also called glycans, which they had made in the laboratory, but “of course, we realized that these not necessarily represent the actual glycans made in animal tissues,” says Cummings.
So the researchers got a hold of lungs from regular pigs and pigs that were genetically engineered to be free of all germs. “We wanted to make sure the glycan structures in the normal pigs were not affected by prior infections or exposure to microbes and so on. So we checked that using germ-free tissues,” explains Cummings.
The researchers stripped off the glycans and the glycolipids from the lungs. They then looked at which glycans from the pig lung could support interactions with different types of influenza viruses.
Glycans come in one of two types, O-linked and N-linked. N-glycans are covalently attached to protein at asparagine residues; O- linked glycans are often linked from a sugar moeity called N-acetylgalactosamine to a hydroxyl group of a serine or threonine residue in proteins. The team demonstrated that the viruses bound to N-linked glycans but not O-linked glycans or glycolipids. “However, each virus tested had different glycan specificities,” Cummings says. “The findings indicate that influenza binding is far more complex than is currently appreciated in the influenza field.” He adds that the results from the normal pigs and germ-free pig lungs are the same.
He adds that study also highlights the fact that researchers actually don’t know the proper identity and distribution of the natural receptors for influenza virus in either the pig or the human respiratory tract. To date, he explains, much of the information about the virus binding to human cells has been derived from experiments done with methods that are not very sensitive and precise, using lectins derived from plants that have questionable specificity and activity for recognizing glycans.
Cummings says that the findings could help us prepare for future pandemics by understanding the specific N-linked glycans a particular influenza viral strain binds to.