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Immune system: allergies as protective function of the body
All over the world more and more people are affected by allergies. According to a representative Forsa survey published in February, around 25 million people in Germany live with one or more allergies. That is almost a third of the entire population. However, doctors cannot answer why allergies are on the rise.
According to the so-called hygiene hypothesis, allergic reactions result from insufficient stress on the immune system in childhood, which develop as a result of excessive hygiene behavior. The sterile environment in which children grow up today means that the body no longer produces adequate immune protection. Another widespread hypothesis is that allergic reactions have arisen as a defense mechanism against parasites.
In a German-American mouse study, researchers led by Philipp Starkl from Stanford University came to the conclusion that allergic reactions could have arisen as protection against toxins. The evolutionary biologist Margie Profet had already set up this theory in 1991, which has been the subject of discussion among medical experts to this day.
The mice were initially injected with small amounts of bee venom. The dose was increased as the study progressed. The researchers were able to observe how resistance developed. "Like a vaccination, the body seemed to be building some kind of immune protection against the bee venom," Starkl explained. The investigations showed that the so-called immunoglobulin (IgE) plays a crucial role in the body's immune response. The proteins, also known colloquially as antibodies, are formed by the body in response to certain substances. For example, the body produces large amounts of these antibodies after a bee sting. As a result of the release of histamine, inflammatory reactions can be seen on the skin, which in severe cases can lead to anaphylactic shock.
In order to find out whether IgE antibodies or another form of immunoglobulin are responsible for the protective reaction, the researchers stopped the formation of IgE in the mice. It was shown that these mice had no protection against the bee venom. As a result, the IgE antibodies must be responsible for immune protection, the researchers concluded.
"In our view, the assumption that the function of IgE antibodies is limited to triggering allergic reactions has always been too short," said Thomas Marichal, co-author of the study published in the journal "Immunity". "Otherwise, IgE antibodies would surely have been eliminated in the course of evolution." This consideration also supports the poison hypothesis put forward by Margie Profet in the early 1990s.
IgE antibodies therefore take on a protective function against toxic substances and must have played an important role in the evolution of mankind, which regressed in the course of increasingly protected living conditions. (fr)
Image: Günther Richter / pixelio.de