Sore nose, itching, shortness of breath …: Why do people have this unpleasant tendency to develop allergies? In the course of evolution, the body has stuck to its well-known “allergy module” because it serves to defend itself against bacteria, study results now suggest. The system of immunoglobulin E antibodies (IgE) and mast cells, which causes allergic reactions, protects against renewed infections with the “hospital germ” Staphylococcus aureus, according to studies on mice.
It is an extremely widespread plague – almost every second European is affected by an allergy: plant pollen, house dust, certain foods and many other substances trigger unpleasant or even dangerous overreactions of the immune system. Research has therefore long focused on allergies, but some aspects are still unclear. It is known that a certain module of the immune system plays a central role in the overreaction to the actually harmless substances.
Allergy patients go through a process of so-called “sensitization” at the beginning of the illness. The immune system develops a certain category of immunoglobulins: IgE antibodies, which are directed at the allergy-triggering foreign substances. Upon renewed contact with the allergen, the IgE antibodies mediate the activation of special defense cells of the immune system: the so-called mast cells then release histamines, proteases or various cytokines in the affected tissues, which are responsible for the typical allergic symptoms. Despite many years of research, the original biological function of this “allergy module” has not yet been fully clarified.
What is the purpose of the problematic system?
The question therefore also arises why this system has been preserved in the course of evolution despite its susceptibility to overreactions. It can be assumed that the interaction between IgE and mast cells does not only play a problematic role in the form of an allergy. In this context, earlier studies have already provided indications of the importance of the complex in the resistance to bee stings and the poisons of certain snakes. The current study by the researchers led by Philipp Starkl from the Medical University of Vienna is based on this: The scientists have investigated whether mast cells and IgE antibodies also play a role in the defense against toxin-producing bacteria.
Because of its medical importance and its broad arsenal of toxins, the scientists selected the infamous hospital germ Staphylococcus aureus as a model bacterium for their studies. As part of the study, they infected mice from genetically modified lines with the pathogen. In addition, they carried out studies on mast cell models in the laboratory in order to decipher the functions of certain components of the IgE effector mechanism.
Protection against toxic bacteria
The researchers found that mice that had mild skin infections with Staphylococcus aureus developed specific IgE antibodies to bacterial components. This immune response then gave the mice an increased resistance to severe lung or skin and tissue infections with the pathogen, the experiments showed. Mice from genetically modified breeding lines that lacked the IgE effector mechanism or the mast cells, on the other hand, were unable to build up protection against the renewed severe infections, report Starkl and his colleagues.
These results indicate that the “allergic” immune response is not exclusively pathological, but can have a protective effect in the event of bacterial infections. Defense against toxin-producing pathogens such as Staphylococcus aureus could therefore be an important biological function of the “allergy module”, the scientists sum up.
The discovery now contributes to a better understanding of the immune system and, above all, of allergic immune reactions. In addition, it also provides a possible explanation for why humans have stuck to the “allergy module” in the course of evolution, although in the case of particular sensitivity to certain foreign substances it can even cause life-threatening complications. The importance of the protective function against poisons and infections by toxin-producing bacteria possibly outweighed this risk.
Source: CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, specialist article: Immunity, doi: 10.1016 / j.immuni.2020.08.002