With the spread of the new coronavirus pneumonia epidemic around the world, people from all over the world have come up with more and more strange ideas to "enhance immunity".
Recently, in "Science and Translational Medicine", there is a new study: eating too much salt may not enhance immunity, but will affect the local microenvironment and glucocorticoid secretion, inhibit neutrophils against bacteria Infected humoral immunity.
This is the first scientific evidence to prove that the high salt environment in the human body will affect immunity.
The high-salt diet poses a cardiovascular threat. Singularity cakes are definitely not nagging, but the impact on the immune system is a controversial topic.
Previous studies have found that high-salt diets are pro-inflammatory in general and are beneficial for maintaining immune function. For example, the skin needs salt to defend against foreign bacteria.
But for the internal organs, the impact of high-salt diet is not easy to say, especially the kidneys and urinary system responsible for removing salt from the body, because urinary tract infections are almost the highest incidence of bacterial infections, if high salt is really good for immune function, there should be more infections in the salty place, right?
So, starting from the urinary tract infection, the team of the University of Bonn in Germany carried out this study. The research team set up three groups of mice, a high-salt diet, a normal diet, and low-salt diet, and induced pyelonephritis caused by E. coli after one week of feeding.
What the research team did not expect was that the inflammation in the high-salt diet group was the most severe, and the number of E. coli colonized in the kidney was 4-6 times that of the ordinary diet group!
Reflected in fluorescent staining, it is bright green E. coli, obviously more high-salt diet (HSD) group on the right.
If we find anomalies, we have to find the reason. The research team compared the conditions of the two groups of mice and found that there was only one obvious difference: Although the neutrophils engulfed a lot of E. coli in the kidneys of mice in the high-salt diet group. However, they cannot be killed, and the ability to kill bacteria is greatly reduced.
The weak neutrophil sterilization ability is definitely inconsistent with the previous "high salt diet pro-inflammatory". The research team compared the previous papers and found that in this test, the sodium level in the kidney did not increase, but instead Is to increase the level of another inflammatory mediator-activated T cell nuclear factor 5 (Nfat5).
Nfat5 itself has little significance for urinary tract infection, but it is also elevated in the spleen of mice, indicating that it should be regulated by a systemic factor. The research team soon confirmed that it is the familiar glucocorticoid that regulates Nfat5, and the increase in glucocorticoid is due to the excessive sodium excreted by the kidney, which activates the adrenal glands.
One of the clinical uses of glucocorticoids is to suppress an excessive immune response, and this effect is still systemic.
The research team inoculated mice with Listeria monocytogenes showed that under a high-salt diet, the number of infected Listeria monocytogenes in the spleen and liver will be 100-1000 times that of normal mice!
If the multiple is a little more, it is estimated that a high-salt diet can turn people into a bacterial petri dish ... but the research team also found that a glucocorticoid alone is not enough to explain the specificity of the infection in the kidney. The urea produced will also weaken the bactericidal ability of neutrophils.
This double restriction, even if it is moved to people, also has a huge impact. The research team called up data from a previous small-scale clinical trial and found that a week of high-salt diet was enough to reduce the body's neutrophils' combat effectiveness and glucocorticoid levels also showed similar changes in the mouse experiment.
In the words of the corresponding author of the paper, Professor Christian Kurts, "We let volunteers eat 6 grams of salt every day, sounds a lot right, but two American fast foods, for example, two hamburgers + two french fries, It will already have such a big impact. "
