In the happy afterglow of Thanksgiving, many Americans will have leftovers for reheating and turning into sandwiches. Unfortunately, there might not be as much leftover turkey as in previous years because of the price increase this year. The cause of the recent jump in turkey price talk? Good, old-fashioned supply and demand – while the number of people eating turkey for Thanksgiving remained the same, the supply was decimated this year by avian influenza (although most reports now state that most consumer prices weren’t affected by this epidemic).
Not every strain of influenza can jump between species, and some are spread more easily between different bird species than they are between birds and mammals such as pigs or humans. This year, turkeys in Minnesotan and Iowan farms were hit hard, with 9 million turkeys killed or culled to prevent the spread of disease – thus the basis of this year’s price scare.
This impact on the food supply is yet another reason why avian influenza is no joke (the primary reason being its potential for human pandemic disease, of course). One way to address both medical and agricultural needs is to study the avian immune response to influenza – medication or vaccination of poultry could help stem either of these scenarios from spreading too far.
It’s with these purposes in mind that researchers have been studying how ducks, one of the natural hosts of Influenza A Virus (IAV), fight off infection. Researchers in Dr. Katharine Magor’s lab have been looking at aspects of the duck immune response to IAV infection, including parts of the innate immune system. As part of the immune system, ducks (and humans) have Interferon Inducible Transmembrane Proteins (IFITMs), proteins that sit in lipid membranes and are activated in response to a number of different viral infections. Some IFITM members, such as IFITM3, are found in the endosomal membrane. Because influenza interacts with endosomes as it enters a host cell, the scientists hypothesized that IFITMs may act as part of the poultry anti-influenza response. Their study is now available from the Journal of Virology
The duck genome has four different IFITM genes, each of which was expressed in chicken cells to test its response against IAV. Using fluorescence microscopy, they first investigated where in the cell the proteins were found. IFITM3 colocalized with the endosomal marker LAMP1, while IFITM1 was found at the cell membrane – indicating that IFITM3 was a stronger candidate to fight influenza infection. Indeed, the chicken cells expressing IFITM3 were better able to fight off influenza infection than IFITM1 or IFITM2.
Entering through endocytosis is a common route of viral entry. To see if this IFITM3 was specific in protecting against influenza, the researchers infected chicken cells with vesicular stomatitis virus (VSV), which also enters through an endosome but escapes at an earlier stage in endosome maturation. Chicken cells expressing IFITM3 protected the cells from influenza virus, but not VSV infection – showing there is a specific protection from IFITM3 against influenza virus.
The researchers demonstrated that duck IFITM3, which has homologs found in pigs and humans, is important for the immune response to influenza virus infection. In other animals, IFITM antiviral activity relies on manipulating lipid composition, and the activity of family member IFITM1 can be negatively impacted by lipid-modulating drugs such as Amphotericin B, an antifungal that binds to sterols. We may someday be able to manipulate IFITM levels with vaccines or antiviral compounds to protect our livestock (and ourselves!) from this dangerous and highly contagious virus.
-- Julie Wolf