Bacteria in fermented food interact with our immune system

27-May-2019 - Germany

Lactic acid bacteria are good for the body and play a central role in our health. Just why this is the case has so far been largely a mystery. Now scientists at Leipzig University have discovered that humans and apes have a cell receptor that is activated by signals from bacteria found in fermented foods. The study thus provides new insights into the evolutionary dynamics between microbes and the immune system. The scientists have recently published their results in the specialist journal PLOS Genetics.

Lactic acid bacteria, which convert milk into yoghurt and cabbage into sauerkraut, have a beneficial effect on the human organism. They are either ingested with fermented food or permanently colonise the intestine. For the first time, scientists from Leipzig have now demonstrated the molecular mechanisms by which lactic acid bacteria interact with our bodies. The researchers began by examining proteins on the surface of cells called hydroxycarboxylic acid (HCA) receptors. While most mammals have two types of this receptor, humans and apes possess a third: HCA3. “We combined evolutionary, pharmacological, immunological and analytical methods and investigated why we retained this receptor during evolution,” said project head Dr Claudia Stäubert from the Faculty of Medicine’s Rudolf Schönheimer Institute of Biochemistry. Our human ancestors lived on earth at a time of great change, which also affected their habitat and thus their food supply. This gave rise to a new lifestyle characterised by less fresh fruit being available, with our ancestors consuming more fermented fallen fruit. Against this backdrop, having the HCA3 receptor may have been a crucial advantage. “In the course of this study, we discovered that a substance found in high concentrations in fermented foods like sauerkraut activates the HCA3 receptor, thus influencing the function of the human immune system,” explained Stäubert. With their study, Stäubert and her team were able to show that after eating sauerkraut, a substance called D-phenyllactic acid can be detected in sufficient concentrations in the blood to stimulate the HCA3 receptor. “Our evolutionary and functional analyses support the hypothesis that this receptor has been retained in humans and great apes during evolution as a new signalling system to address functions of the immune system,” summarised Stäubert. Via the receptor, the newly discovered substance D-phenyllactic acid communicates to the immune system and fat cells that both foreign substances and energy have entered the body.
“Countless studies show positive effects of consuming lactic acid bacteria and fermented food. We are convinced that HCA3 must be responsible for some of these effects,” continued Stäubert. Future research will investigate how exactly D-phenyllactic acid affects the immune system and energy storage, in order to find out whether HCA3 could also serve as a therapeutic target, for example in the treatment of irritable bowel syndrome. The study by the Rudolf Schönheimer Institute of Biochemistry with director Professor Torsten Schöneberg was carried out in cooperation with the Institute of Laboratory Medicine, Clinical Chemistry and Molecular Diagnostics at Leipzig University Hospital, Helmholtz Centre for Environmental Research - UFZ as well as the German Centre for Integrative Biodiversity Research (iDiv).