The Human Microbiome Project has been underway since 2008, and the microbiome itself is haltingly making its way into the mainstream news. The human microbiome is the vast mosaic of microbes living on and inside the human body: the ears, tongue, cheeks, gut, nose, skin, vagina, and stool each host populations of archaea and bacteria. A cascade of new observations links any piece of this puzzle to different conditions in health and disease.

As an example, rheumatoid arthritis–related autoimmunity may be initiated at a mucosal site years before the onset of joint symptoms (1). The candidate sites of origin include the oral, lung, and gastrointestinal mucosa. Moreover, autoimmunity and inflammation are not limited to specific rheumatologic and inflammatory disorders, but represent a driving force in the pathogenesis of cardiovascular and metabolic diseases. Accordingly, the relations among gut microbiota, energy homeostasis, and inflammation, as well as their roles in obesity-related disorders, are increasingly recognized (2).

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