免疫系统疾病 z-bo 2020-09-19 384

　　I don’t know if you have noticed a strange phenomenon: Children who often haunt the farm and other environments that are not particularly clean are less likely to get allergies, asthma and other immune system disorders than children in the city. This phenomenon led scientists to pay attention to the relationship between the environment and allergic diseases, and some scholars later put forward the theory of "hygiene hypothesis".

　　"Hygiene Hypothesis" believes that the more children are exposed to infection in early childhood, the lower the probability of developing allergic diseases in the future. Conversely, if children are less likely to be exposed to dust and microorganisms, they will be more likely to suffer from diseases such as allergies or asthma.

　　In order to further reveal the mechanism of this theory, studies have found that a bacterial protein, endotoxin, can suppress an overactive immune system. Endotoxin is present in many common bacteria, such as E. coli. These common bacteria are relatively more present in agricultural environments.

　　Professor Bart Lambrecht of Ghent University in Belgium and his research team have recently discovered that there is a key enzyme in the human body, A20, which can effectively defend against allergies, asthma and other immune diseases. However, people who lack this enzyme cannot effectively alleviate allergic symptoms even if they are exposed to endotoxins.

　　A20+ endotoxin, effective defense against immune system overload

　　A20 plays an important role in controlling inflammation and is activated when a newborn baby comes into contact with benign bacteria in the birth canal. Research evidence shows that the enzyme can help build the baby's immune system. If the gene encoding A20 is mutated, it will cause its dysfunction, making it more prone to asthma and allergic symptoms.

　　The research team conducted a study on the association between A20 and endotoxin. Normal mice and mice that do not secrete A20 after genetic engineering were used as test subjects. The two groups of test mice were exposed to an environment rich in endotoxin for two weeks to test the effect of endotoxin on them. Because dust mites are a common cause of allergies in mice and humans, the researchers used the sensitivity of mice to dust mites as an indicator.

　　The data showed that none of the normal mice showed allergic reactions to mites, even some normal mice in the control group (not exposed to endotoxin) had allergic reactions. However, test mice lacking A20 are allergic to dust mites even when exposed to endotoxins. In addition, they also found that A20 expression is low in adults with asthma.

　　The above data shows that endotoxin triggers an immune response and promotes the expression of A20. The two complement each other and effectively ensure that the immune system does not respond abnormally.

　　The controversy surrounding the research

　　Erika von Mutius, a professor at the University of Munich in Germany and the main advocate of the hygiene hypothesis, said: "The results of this study are very important because it proves that when endotoxins alone exist, they will not affect the immune response." Her early work focused on Since resistance to endotoxins can protect children growing up on the farm and prevent allergic reactions, this new study further provides a strong proof of the function of the bacterial protein.

　　However, William Parker of Duke University Medical Center does not believe that endotoxin can explain why urban residents have relatively more allergic diseases. On the contrary, Parker believes that lack of exposure to parasites similar to lice or worms is the culprit of allergies, because even intestinal worms that do not secrete endotoxins can cause an overreaction in the western immune system.

　　So, what is the real mechanism? Let us look forward to more powerful research reports.