A common food additive, found in frozen meat and fried foods, may hinder the immune system's ability to fight influenza and reduce the effectiveness of the flu vaccine, a study has found.
The research may help explain why seasonal influenza continues to pose a major health threat worldwide. An estimated 290,000-650,000 people globally die from flu-related respiratory problems each year.
The research conducted in mice suggests that the food additive tert-butylhydroquinone (tBHQ) affects the T cells, a vital component of the immune system.
The additive tBHQ is used to prevent spoilage, with a maximum allowed concentration of 200 parts per million in food products.
"Our studies showed that mice on a tBHQ diet had a weakened immune response to influenza (flu) infection," said Robert Freeborn, a PhD candidate at Michigan State University in the US.
"In our mouse model, tBHQ suppressed the function of two types of T cells, helper and killer T cells. Ultimately, this led to more severe symptoms during a subsequent influenza infection," Freeborn said in a statement.
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When a person is infected with influenza virus, helper T cells direct other parts of the immune system and help coordinate an appropriate response, while killer T cells hunt down infected cells and clear them from the body.
In their experiments, the researchers found mice eating a tBHQ-spiked diet were slower to activate both helper T cells and killer T cells, resulting in slower clearance of the virus.
"Right now, my leading hypothesis is that tBHQ causes these effects by upregulating some proteins which are known to suppress the immune system," said Freeborn.
"Expression of these proteins, CTLA-4 and IL-10, was upregulated in two different models we use in the lab. However, more work is necessary to determine if upregulation of these suppressive proteins is indeed causative for the effects of tBHQ during influenza infection," he said.
When the mice were later re-infected with a different but related strain of influenza, those on the tBHQ diet had a longer illness and lost more weight.
This suggests that tBHQ impaired the "memory response" that typically primes the immune system to fight a second infection, Freeborn said.
Since the memory response is central to how vaccines work, impairment of this function could potentially reduce the efficacy of the flu vaccine.
T cells are involved in the immune response to a variety of diseases, so tBHQ could also play a role in other types of infectious diseases, Freeborn added.
"It can be hard to know if you are consuming tBHQ, as it is not always listed on ingredient labels," said Freeborn, adding that this is often the case when tBHQ is used in food preparation, such as in the oil used to fry a chip.
"The best way to limit tBHQ exposure is to be cognizant about food choices. Since tBHQ is largely used to stabilize fats, a low-fat diet and cutting down on processed snacks will help reduce tBHQ consumption," he said.