A food additive that manufacturers commonly add to frozen meat could make it harder for us to fight influenza viruses.
Many of us have had the flu at some point and treated it with nothing more than bed rest and lots of fluids. However, although the flu may sound like a relatively innocuous condition, it actually continues to cause a significant number of deaths both worldwide and in the United States.
So, researchers are still interested in finding out more about factors that either raise the risk of contracting influenza, make the illness more severe, or are likely to hinder the efficacy of influenza vaccines.
Now, Robert Freeborn, a doctoral researcher at Michigan State University in East Lansing, and a team of researchers have found that a common food additive is one such factor that suppresses the body's immune response and weakens it in the fight against the flu.
The food additive bears the name "tert-butylhydroquinone" (tBHQ), and it is a synthetic antioxidant that prevents the oils and fats in foods from deteriorating through oxidation. This additive is often present in frozen meat, crackers, and fried foods.
Freeborn and colleagues carried out their study in mice and presented their findings at the American Society for Pharmacology and Experimental Therapeutics annual meeting, which takes place in April in Orlando, FL.
How tBHQ impairs the immune response
So-called "helper" T cells are key in the fight against influenza viruses that invade the body. Helper T cells coordinate the efforts of other components of the immune system while "killer" T cells target and destroy infected cells.
Using a mouse model of influenza infection, Freeborn and colleagues fed one group of rodents a diet with added tBHQ while another group of rodents ate a standard diet.
The researchers found that both helper and killer T cells activated much more slowly in the mice that had eaten a tBHQ-enhanced diet. As a result, the virus took much longer to clear.
"Our studies showed that mice on a tBHQ diet had a weakened immune response to influenza (flu) infection," comments Freeborn.
"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."
Furthermore, when the researchers reinfected the rodents with a new, similar strain of influenza, they found that the mice on the tBHQ diet were sick for longer and lost more weight.
This, the researchers explain, suggests that the additive interferes with the so-called "memory response" that helps the immune system fight a second infection.
How much tBHQ do you consume?
The study's first author offers some insight into the potential mechanisms that may explain the effect of this food additive on the immune response.
"Right now, my leading hypothesis is that tBHQ causes these effects by upregulating some proteins [that] are known to suppress the immune system," says 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."
In their research, the scientists used a dose of tBHQ that is equivalent to estimates of typical human consumption. However, Freeborn and colleagues point out that it is hard to tell how much tBHQ people are eating in reality.
Diet models have led scientists to estimate that some U.S. individuals consume almost double the maximum amount that expert organizations allow.
"It can be hard to know if you are consuming tBHQ, as it is not always listed on ingredient labels," says Freeborn. Moreover, there is often added tBHQ in the oil that people use to fry chips, for instance, which makes it even harder to detect.
"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."