S. Hapfelmeier (Gut microbiology lab)

Research Focus - Immunology of mucosal infection

One may not like the thought of it, but the cells of the human body form merely a minority within a “human superorganism” that is dominated by bacteria. Vast numbers of non-pathogenic microbes (the “microbiota”) colonize the body surfaces, most of them in the lower intestinal tract that contains up 1014 bacteria, roughly 10 times the total number of human cells. The fact that we and other higher vertebrates can live healthily with this bacterial burden is owed to the non-pathogenic, or even symbiotic, nature of the microbiota and the enormously efficient and flexible mucosal immune system.

The mucosal immune system is an extremely robust system that allows the disease-free coexistence with a very broad spectrum of microorganisms. It combines mechanisms to fight off pathogenic microbes with the ability to avoid deleterious responses towards the non-pathogenic microbiota. This is a balancing act since the protection from sepsis by spontaneous penetration of microbiota components also requires very efficient immune protection that is, however, rather non-inflammatory. On top of this, the mucosal immune system somehow retains a selective responsiveness towards pathogenic microbes that are countered with inflammation and bactericidal activities.

Pathogen Infection and Commensal Colonization
S. Hapfelmeier

Our main research focus is on the unknown mechanisms of immune discrimination between pathogenic and non-pathogenic bacteria. How can the immune system identify and selectively respond to pathogenic bacteria in the massive presence of diverse non-pathogenic bacteria? No innate immune receptors so far are known to recognize molecular patterns that are unique to pathogens and absent from commensal bacteria. How can the immune system still safely discriminate? Finding answers to these questions would be important for the development of efficient mucosal vaccines and a better understanding of the aberrant immune responses towards the non-pathogenic microbiota seen in inflammatory bowel diseases like Crohn’s disease.