Stomach microbiota,Helicobacter pylori, and group 2 innate lymphoid cells

The stomach has been thought to host few commensal bacteria because of the existence of barriers, such as gastric acid. However, recent culture-independent, sequencing-based microbial analysis has shown that the stomach also harbors a wide diversity of microbiota. Although the stomach immune system, especially innate lymphoid cells (ILCs), has not been well elucidated, recent studies have shown that group 2 ILCs (ILC2s) are the dominant subtype in the stomach of both humans and mice. Stomach ILC2s are unique in that their existence is dependent on stomach microbiota, in sharp contrast to the lack of an impact of commensal microbiota on ILC2s in other tissues. The microbiota dependency of stomach ILC2s is partly explained by their responsiveness to interleukin (IL)-7. Stomach ILC2s express significantly higher IL-7 receptor protein levels on their surface and proliferate more in response to IL-7 stimulation in vitro than small intestinal ILC2s. Consistently, the stomach expresses much higher IL-7 protein levels than the small intestine. IL-5 secreted from stomach ILC2s promotes immunoglobulin (Ig) A production by plasma B cells. In a murine model, stomach ILC2s are important in containingHelicobacter pyloriinfection, especially in the early phase of infection, by promoting IgA production. Gut microbiome: a surprise in the stomach The stomach's microbiota, and its effect on immune development, may be key factors in fending off infection withHelicobacter pylori, a bacterium found in the stomach that can lead to gastric upset and, if left untreated, ulcers or stomach cancer. Unlike the intestines, the stomach was thought to contain few bacteria owing to its high acidity, but according to new studies, the stomach harbors its own set of microbiota. Hiroshi Ohno and Naoko Satoh-Takayama at the RIKEN Center for Integrative Medical Sciences and Yokohama City University, Japan, review how gastric microbiota affects development of immune cells in the stomach. They report that the stomach's unique microbiota influences maturation of particular immune cells, which may be crucial in fighting offH. pyloriinfection. These findings illuminate a new area in microbiome research.