Figure 1.

A very basic view of epithelial barrier function—separation of a multitude of different luminal compartments from the vasculature. Communication of these luminal compartments in many cases with the outside environment makes them rife with allergens and pathogens. The immune system, being situated primarily in the vascular compartment, places an enormous premium on barrier integrity segregating the immune system from its activators in these luminal compartments. Failure to separate can then lead to severe and/or chronic inflammation.