While some people are regularly affected by sinusitis, others are hardly ever affected by these infections. This resistance in some people is due to the action of bitterness receptors present in the respiratory tract.
Several substances hazardous to health have the common characteristic of being very bitter. To protect the body from the harmful impact of these substances, the taste receptors present on the tongue contain several receptors specialized in the detection of bitterness: as soon as the bitter molecule mixes with saliva, it is captured by these receptors and a nerve message is immediately sent to the brain to trigger an instinctive reaction of rejection.
The importance of this mechanism for survival is well illustrated by the number and efficiency of bitterness receptors: for example, whereas the detection of sugar involves only 2 receptors, at least 50 distinct receptors perceive bitterness. bitterness, 1000 times more sensitive than sugar!
Curiously, there are interindividual genetic variations that make some people even more susceptible to bitterness; for example, people who have a modified version of certain receptors (called T2R38) are much more sensitive to this flavor. The reason for this diversity remains unknown, but some specialists believe that it could mean that these receptors have other functions than the detection of bitter taste.
On the front line against pathogens
A major breakthrough in this direction comes from the observation that bitterness receptors are also present on the surface of the cells that line the upper respiratory tract (nose and sinuses). This location is at first sight surprising, because the role of the respiratory mucosa is to act as the first line of defense against the pathogens present in the air we breathe: these cells secrete a mucus which makes it possible to coat foreign substances and they also have cilia on their surface which create a movement allowing the particles to be transported towards the pharynx, where they are swallowed or eliminated by expectoration. At the same time, the beating of the eyelashes causes the formation of nitric oxide, a gas endowed with antimicrobial properties which “disinfects” the respiratory tract.
Being sensitive to bitterness is a very good sign
Bitterness receptors participate in this defense mechanism by detecting certain bitter substances secreted by bacteria present in the respiratory tract. The experiments showed that the production of these compounds (sesquiterpene lactones) by the respiratory pathogen Pseudomonas aeruginosa activated the T2R38 receptor, which led to an increase in the beat frequency of the cilia responsible for the elimination of particles as well as an increase in the production of nitric oxide by the mucous membrane. The researchers also observed that the effectiveness of this mechanism differs greatly depending on the type of T2R38 receptor that is present in the mucosa and which varies from person to person.
Thus, the sinuses of people who have the most active version of this receptor (and therefore who are therefore more sensitive to bitter taste) were completely free of pathogens, while those of people whose receptor is less active are much more at risk. to get infected and develop sinusitis.
The greater vulnerability of some people to respiratory infections would therefore be caused, at least in part, by variations in certain bitterness receptors. The identification of factors that can improve the activity of these receptors could therefore represent a new avenue for the treatment of these infections, in particular chronic sinusitis.
Lee RJ et al. T2R38 taste receptor polymorphisms underlie susceptibility to upper respiratory infection. J. Clin. Invest. 122:4145-59.
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