People with infections and autoimmune diseases, or other inflammatory conditions have higher levels of the protein tumor necrosis factor than healthy people, which can influence the sensitivity to bitter tastes.

When we are sick, we have less appetite for food; especially for bitter food. A team of scientists have just discovered in mice that may cause a misleading sensation. Apparently, the protein tumor necrosis factor α (TNF-α), a molecule involved in the immune system, could change the eating habits of patients by influencing the taste receptors of the tongue.

The researchers, led by Hong Wang of the Monell Chemical Senses Center in Philadelphia, offered water with different flavors and concentrations to transgenic mice lacking the TNF-α protein and to healthy mice. They noted that GM showed typical sweet, sour, and salty flavors reactions; however, they were less sensitive to bitter taste.

The effect on the taste buds

“Normal mice noticed [the flavor] at much lower concentrations; they knew that it was bitter and were not going to like”, Wang said. “However, those which lacked the TNF-α gene avoided the bitter solution only at high concentrations”, he said. Usually, mice shy away from these foods because they associate them with inedible or poisonous substances.

To determine whether TNF-α acted on taste buds or suppressed relevant stimuli in the brain, the team recorded electrical activity in the nerves that transmit taste signals to the brain from the tongue. They found that fewer neurons were activated in mice that had no TNF-α when taking bitter substances, which, according to the authors, indicates that the protein acts directly on receptors on the tongue. They also found that the TNF-α only influenced the perception of bitter taste, because many cell types of taste buds have receptors for proteins.

Mr. Wang’s study has led to the conclusion that the protein tumor necrosis factor α (TNF-α) is responsible for the higher sensitivity to bitter tastes in the mouth.