New insights have been gained in recent years on the influence of commensal bacteria on our immune system, bacteria that also colonise the mucosal surface of the intestinal tract. However, it has generally been unclear what association there is between B cells and such beneficial or harmless microorganisms. B cells are an essential component of our immune system. They recognise foreign structures and produce specific antibodies.

Hai Li, Julien Limenitakis and Stephanie Ganal-Vonarburg wanted to find out how, when and where the microorganisms influence the B cells on mucosa. The three researchers faced the challenge of both the microbiome and the different B cells forming highly complex and very individual systems. They colonised germ-free mice with different harmless bacterial strains and then sequenced the B cell DNA and their antibodies. This revealed that the bacteria have a clear effect on these immune cells and veritably shape their composition. The repertoire of B cells and their antibody response changed in mice, depending on which bacteria were used and in which form.  

This research highlights how important healthy bacterial flora is for the host organism. Depending on the B cell population that is built up in early life through contact with different microorganisms, the immune system reacts in a variety of ways in the form of inflammation or defensive reactions.

The results of the research conducted by the three scientists from Bern demonstrate in detail how commensal bacteria produce “their” B cell repertoire in the mice that were investigated. As a relevant portion of the colonisation with microorganisms takes place early on in life, shaping of the B cell repertoire during this critical period may also influence subsequent immune responses to infections and vaccinations.

Mucosal or systemic microbiota exposures shape the B cell repertoire. Hai Li*, Julien P Limenitakis*, Victor Greiff, Bahtiyar Yilmaz, Olivier Schären, Camilla Urbaniak, Mirjam Zünd, Melissa A E Lawson, Ian D Young, Sandra Rupp, Mathias Heikenwälder, Kathy D McCoy, Siegfried Hapfelmeier, *Stephanie C Ganal-Vonarburg & *Andrew J Macpherson. 
Nature. 2020 Aug;584(7820):274-278. doi: 10.1038/s41586-020-2564-6.
*These authors contributed equally to this work.