Natural pattern recognition mechanisms at epithelial barriers and potential use in nanomedicine

At epithelial barriers molecular pattern recognition mechanisms act as minesweepers against harmful environmental factors and thereby play a crucial role in the defense against invading bacterial and viral pathogens. However, it became evident that some of the proteins participating in these host defense processes may simultaneously function as regulators of tissue regeneration when in the extracellular matrix, thus coupling defense functions with regulation of stem cells. Although molecular pattern recognition has complex physiological roles and we just begin to understand its various functions, the simplicity of the underlying principles for recognition of specific classes of molecules may generate novel starting points for nanomedical approaches in drug delivery across epithelial barriers. The present article aims to provide an introduction into the biological context, processes, proteins, and general mechanisms of molecular pattern recognition in humans and, by using selected examples, to identify potential areas in nanomedicine for the exploitation of these mechanisms.