Allergies were defense against poison

Immune System: Allergies as a protective function of the body

26/11/2013

More and more people worldwide are affected by allergies. According to a representative Forsa survey, published in February, about 25 million people in Germany live with one or more allergies. That's almost a third of the total population. But why allergies are on the rise, medics can not answer.

According to the so-called hygiene hypothesis, allergic reactions arise from lack of 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 makes the body produce inadequate immune protection. Another widespread hypothesis is that allergic reactions have emerged as a defense mechanism against parasites.

Researchers led by Philipp Starkl of Stanford University, come in a German-American mouse study to the conclusion that allergic reactions may have originated as protection against poisons. Already in 1991, the evolutionary biologist Margie Profet had set up this theory, which continues to provide discussion amongst medical professionals today.

The mice were initially injected with small amounts of bee venom. The dose was increased later in the study. The researchers were able to observe how resistance developed. "Like a vaccine, the body seemed to be building some kind of immune protection against bee venom," Starkl said. During the investigations it could be seen that the so-called immunoglobulin (IgE) plays a decisive role in the defense reaction of the body. The colloquially known as antibodies proteins are formed in response to certain substances from the body. For example, after a bee sting, the body produces large quantities of these antibodies. As a result of histamine release inflammatory reactions on the skin are recognizable, which can degenerate in severe cases in anaphylactic shock.

To find out whether IgE antibodies or another form of the immunoglobulin are responsible for the protective reaction, the researchers have in another experiment in mice inhibited the formation of IgE. It turned out that these mice had no protection against bee venom. Consequently, IgE antibodies must be responsible for immune protection, the researchers concluded.

"The assumption that the function of IgE antibodies is limited to the triggering of allergic reactions has, in our view, always been too short," said Thomas Marichal, co-author of the study published in the journal "Immunity". "Otherwise, IgE antibodies would have been safely eliminated in the course of evolution." This consideration also supports the poison hypothesis established by Margie Profet in the early 1990s.

Accordingly, IgE antibodies function as a protective function against toxic substances and must have played an important role in the evolution of mankind, which regressed in the course of ever more sheltered living conditions. (Fr)

Picture: Günther Richter