Innate immune recognition on the intestinal mucosa.

The discovery of transcriptionally activating receptors for microbial structures has provided a deeper understanding of how the immune system manages to sense and localize the presence of harmful microbes and target and shape the adequate host response. However, the recognized microbial structures are common to pathogens and commensal microbes and many body surfaces are constantly exposed to environmental microbial ligands and densely colonized by a bacterial flora such as seen for example in the intestinal tract. Thus, mechanisms must exist that facilitate discrimination between benign and beneficial colonization and potentially harmful invasive infection. Identification of the mechanisms involved and characterization of the underlying molecular processes will add to our understanding of mucosal immune defense and might unravel the etiology and pathogenesis of so far undefined inflammatory conditions. Here, we will discuss factors that might be involved to control inappropriate innate immune activation and ensure the host-microbe homeostasis in the intestinal tract.