The mucosal microbiome in shaping health and disease.

More than 300 years after Antonie van Leeuwenhoek gave the first description of microbes that colonize human body surfaces, the re-discovery of this multifaceted microbial world within our bodies has challenged our principal view on microbes. Novel sequencing techniques provide a plethora of (meta)genomic data, which elucidate the unique properties of mircobiota in different subjects. Moreover, the variety of metabolic and immunologic interactions between the mircobiota and the host's epithelial surfaces has challenged the paradigm of a unidirectional interplay between a given pathogen and the host's immune defense. The newly discovered mechanisms that underlie the symbiosis between the host, specific colonizers, and the mircobiota as a whole indicate that this colonization is more than a friendly coexistence. In fact, it represents a complex ecosystem with implications for the human metabolic homeostasis and immune tolerance. The resilience of the mircobiota and the capability to maintain a well-established equilibrium between symbionts and potential pathogens seem to be determining factors in shaping health or disease.