Out of the trillions of "friendly" bacteria - representing hundreds of species -that make our intestines their home, new evidence in mice suggests that it may be a very select few that shape our immune responses. The findings detailed in two October 16th reports appearing in the journals Cell and Immunity, both Cell Press publications, offer new insight into the constant dialogue that goes on between intestinal microbes and the immune system, and point to a remarkably big role for a class of microbes known as segmented filamentous bacteria (SFB). "It's the first example of a commensal bacteria that can induce accumulation in the gut of a highly specific branch of the immune system," said Dan Littman of the Howard Hughes Medical Institute and the New York University School of Medicine, who led the study reported in Cell. "We're headed into an exciting new area, and we hope more pieces of how the microbial-host interaction contributes to health will begin to fall into place." "Our study provides the surprising result that among the hundreds of bacterial species composing the gut microbiota -- only a very small number, the prototype of which is SFB -- can efficiently stimulate the post-natal physiologic maturation of the immune barrier," added Valérie Gaboriau-Routhiau of INSERM in France, who led the Immunity report. "A unique feature of SFB appears to be its capacity to simultaneously stimulate a large spectrum of intestinal immune responses -- innate and adaptive, pro-inflammatory and regulatory -- which complete and balance each other." Notably, those SFBs stimulate particular types of helper T cells, known as Th17 cells, the studies show. In Littman's case, the findings by his group were something of an accidental discovery. They were studying T cells in the intestine and were getting some inconsistencies in their results. Those inconsistencies could be traced to differences in the gut floras of mice obtained from different sources, and specifically, they found, in the presence or absence of SFB.
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