Unlikely allies against infection

Multitudes of bacteria make themselves a happy home within the mammalian small intestine. However, these residents are not merely freeloaders, but instead ‘earn their keep’ by facilitating host digestion and metabolism, among other functions.

New findings from a research team led by Hiroshi Kiyono of the University of Tokyo, Japan, now offer important insights into another important function of these gut flora, revealing how the bacteria residing within clumps of immune cells known as Peyer’s patches (PPs) contribute to host defense against pathogenic microbes¹. 

Kiyono and colleagues determined that the interior of mouse PPs is largely populated by Alcaligenes, a common opportunistic bacterium. Its presence appears to trigger a highly localized immune response, characterized by elevated levels of IgA antibodies within the gut, without inducing a strong systemic reaction.

These antibodies appear to directly contribute to stable internalization of Alcaligenes within PPs. Conversely, they found that this bacterium is in turn important to proper development and function of the mucosal immune system; without Alcaligenes, mice generate considerably fewer mature IgA-secreting cells.

This bacterium also resides within primate and human PPs, and the authors conclude that these and other findings from their study may hint at contributions of other bacterial species to immune system development at the whole-body level.