Lower risk of asthma with frequent contact with germs
A germ-free environment increases the risk of autoimmune diseases. Contact with germs during "early childhood is associated with protection against autoimmune diseases such as inflammatory bowel diseases and asthma," according to the results of a study by researchers from the Harvard Medical School in Boston and the University Hospital in Kiel, published in the journal "Science".
In the experiment with mice, the researchers were able to confirm previous research results, according to which the significant increase in autoimmune diseases is due to the as sterile environment as possible. If the animals had little or no contact with microbes in childhood, so-called natural T-killer cells accumulated in special tissue layers (the lamina propria), which caused the animals to suffer from chronic inflammatory bowel diseases and asthma, the scientists report in the journal Science ".
Germ-free environment promotes autoimmune diseases It has long been suspected that the germ-free environment in childhood promotes the occurrence of autoimmune diseases and allergies later in life. The researchers led by Torsten Olszak (formerly Harvard Medical School, now Ludwig Maximilians University in Munich) have now uncovered the connection between the occurrence of autoimmune diseases and the lack of contact with germs during early childhood. Apparently, the germs in mice have a significant impact on the development of the immune cells, the researchers report. In the course of their study, the scientists compared the susceptibility to autoimmune diseases in normal laboratory mice and particularly germ-free animals. "Their keeping was complex, they live in specially sealed plastic containers and receive specially prepared feed," explained Torsten Olszak.
A germ-free environment favors the accumulation of T-killer cells. The experiments had shown that "the germ-free mice" have "especially many natural killer T-cells in the lungs and intestines in comparison to the normal laboratory mice", emphasized Olszak. After activation, these natural T-killer cells "release a number of messenger substances that play a role in autoimmune diseases and inflammation," reports the expert. As a result, the germ-free mice were significantly more susceptible to asthma and inflammatory bowel diseases. This raised the question of what could be done about it, continued Olszak. Here the researchers tested different situations. The germ-free mice, for example, were put in a cage with the other laboratory mice at the age of about eight weeks (from this age mice are considered to be adults), in the hope that the immune system could also adapt later. However, the vulnerability of the immune system, which was developed in childhood, could not be remedied in this way.
Germs apparently change the activity of the genes "Then we put pregnant mice from the aseptic population in cages with normal laboratory mice and let them have their babies there", which gave the offspring immediate contact with the naturally occurring germs, explained Torsten Olszak. In the animals born in this way, the number of natural killer T cells normalized and they were significantly less susceptible to asthma and or inflammatory bowel diseases, said Olszak. The question also arose, "How can the adult, germ-free mouse 'remember' that there were no bacteria at the beginning of life," explained the biologist Andre Franke from the Christian-Albrechts-University in Kiel, who was also involved in the study. Here, the researchers found that the information does not appear to be passed on through direct gene changes, but only changes the activity of the genes. "So we were able to explain why a protein of the immune system is more common in the germ-free mice," emphasized Franke.
Hygiene hypothesis as an explanation for autoimmune diseases and allergies Current research results particularly support the so-called hygiene hypothesis, according to which the germ-free environment in childhood has a significant influence on autoimmune diseases and allergies later in life. This was also emphasized by the authors of the accompanying article on the contribution by Olszak and colleagues. Here, for the first time, clear evidence is provided for something "that we have been observing for decades but have not understood," write the US scientists. At the beginning of last year, researchers from Ludwig Maximilians University (LMU) presented the evaluation of two comprehensive studies in the specialist magazine, according to which the more frequent contact of rural children with microorganisms, which caused them to develop asthma less frequently than city children. It also identified some types of bacteria that may help reduce the risk of asthma. Here, the authors of the current study want to follow up and find out which bacteria are particularly protective against autoimmune diseases. However, Olszak and colleagues write that it has yet to be checked whether the causal relationships found in mice can also be transferred to humans. In view of the large number of studies that have now shown a positive effect of contact with germs during childhood, parents should already avoid excessive hygiene in their offspring. Playing in the dirt could be healthier than many other efforts. (fp)
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