Germs prevent autoimmune diseases

Lower risk of asthma in case of frequent contact with germs

23.03.2012

A germ-free environment increases the risk of autoimmune diseases. Because the contact with germs during „Early childhood is associated with protection against autoimmune diseases such as inflammatory bowel disease and asthma, according to the journal „Science“ published results of a study by researchers from Harvard Medical School in Boston and the University Hospital in Kiel.

In the experiment with mice, the researchers were able to confirm earlier research results, according to which the significant increase in autoimmune diseases in the germ-free as possible kept environment. If the animals had little or no contact with microbes in childhood, so-called natural T-killer cells in special tissue layers (the lamina propria) enriched, causing the animals increasingly suffer from chronic inflammatory bowel disease 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, the occurrence of autoimmune diseases and allergies later in life favors. The researchers led by Torsten Olszak (formerly Harvard Medical School, now Ludwig-Maximilians-Universität München) have now deciphered 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 immune cells, the researchers report. The scientists compared their susceptibility to autoimmune disease in normal laboratory mice and particularly germ-free animals. „Their attitude was complex, they live in extra sealed plastic containers and receive specially prepared food“, explained Torsten Olszak.

Germ-free environment favors the accumulation of T-killer cells
The experiments showed that „the germ-free mice“ in comparison to the usual laboratory mice „especially many natural killer T cells in the lung and intestine“, stressed Olszak. Upon activation, these natural T-killer cells shed „a number of messengers that play a role in autoimmune diseases and inflammation“, reports the expert. As a result, the germ-free mice were much more susceptible to asthma and inflammatory bowel disease. This raised the question of what could be done about it, Olszak continued. Here, the researchers tested different situations. For example, at the age of about eight weeks (from which age mice are considered adult), the germ-free mice were placed in a common cage with the other laboratory mice, hoping that the immune system could eventually adapt later. However, the susceptibility of the immune system developed during childhood could not be remedied in this way.

Germs apparently alter the activity of genes
„Then we put pregnant mice from the germ-free population into cages with normal laboratory mice and let them have their babies there“, whereby the offspring immediately had contact with the naturally occurring germs, explained Torsten Olszak. In the so-born animals, the number of natural killer T-cells had normalized and they had a significantly lower susceptibility to asthma and inflammatory bowel disease, so Olszak on. Also, the question arose, „how the adult, germ-free mouse can 'remember' that no bacteria were present at the beginning of life“, explained the biologist Andre Franke, also involved in the study, from the Christian-Albrechts-University in Kiel. Here, the researchers found that the information does not appear to be transmitted by direct gene changes, but only changes the activity of the genes. „So we could explain why an immune system protein is more common in germ-free mice“, stressed Franke.

Hygiene hypothesis as an explanation for autoimmune diseases and allergies
The current research supports in a special way the so-called hygiene hypothesis, according to which the germ-free environment in childhood has a significant impact on autoimmune diseases and allergies later in life. This was also emphasized by the authors of the companion article to the article by Olszak and colleagues. Here, for the first time, clear evidence of something is provided, „that we have been observing for decades, but have not understood“, write the US scientists. At the beginning of last year, researchers from the Ludwig-Maximilians-Universität (LMU) presented in the journal the evaluation of two comprehensive studies, according to which the contact between land children and microorganisms, which caused them to suffer from asthma less frequently, became urban children. It also identified some bacterial species that could potentially help reduce the risk of asthma. Here, the authors of the current study want to link up and find out which bacteria prove to be particularly protective against autoimmune diseases. However, for the time being, it has to be examined whether the causal relationships found in mice can also be transferred to humans, write Olszak and colleagues. However, given the plethora of studies that have now shown a positive impact of exposure to childhood germs, parents should now refrain from exaggerated hygiene in the offspring. Playing in the dirt could be more beneficial to your health than many other efforts. (Fp)

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Picture: Albrecht E. Arnold