Although a bit technical I find this interesting because, again, it demonstrates the powerful importance of a healthy, diverse gut microbiota in regulating human immune systems. These scientists looked at B cells - a key component of the adaptive immune system, which are expected to mitigate against tolerance to grafted tissue from another individual. But, in the presence of a healthy gut microbiota these B cells developed tolerance to the skin grafts. As the authors put it: "We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility “conventional” (CV) facilities (which means a healthy gut microbiota) and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. (This is because IL10 is a key anti-inflammatory cytokine and....) The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells (because it got rid of gut microbes indiscriminately). Finally, we identified transitional B cells isolated from CV facilities
as possessing the regulatory function."