When poet Walt Whitman wrote that we "contain multitudes," he was speaking metaphorically, but he was correct in the literal sense. Every human being carries over 100 trillion individual bacterial cells within the intestine -- ten times more cells than comprise the body itself.

Now, David Artis, PhD, associate professor of Microbiology, along with postdoctoral fellow David Hill, PhD, from the Perelman School of Medicine at the University of Pennsylvania, and collaborators from The Children's Hospital of Philadelphia and institutions in Japan and Germany, have found that these commensal bacteria might play an important role in influencing and controlling allergic inflammation. The commensal relationship that develops between humans and internal bacteria is one in which both humans and bacteria derive benefits.

The study -- appearing this week in Nature Medicine -- suggests that therapeutic targeting of immune cell responses to resident gut bacteria may be beneficial in treating allergic diseases.

The researchers build on previous work demonstrating that selective manipulation of the commensal bacterial population could affect the immune system. "Studies in human patients suggest that changes in commensal populations or exposure to broad spectrum antibiotics can predispose patients to the development of systemic allergic diseases," Hill explains. "In addition, previous studies in animal models have shown that commensal bacteria can influence local immune cells in the intestine. However, the cellular and molecular mechanisms by which commensal bacteria influence the host immune system, in particular the branches of the host immune system that regulate allergic inflammation, are not well understood."

Artis and his colleagues focused on the role of basophils, a type of white blood cell, in causing allergic inflammation, and the relationship between basophil responses and allergic disease.

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