Dendritic cells and toll-like receptors in allergy and asthma.

Epithelia represent a major portal of entry for pathogen microorganisms and allergens and are equipped with innate and adaptive immunity for their protection. Pattern recognition receptors (PRR), including Toll-Like Receptors (TLR), recognize pathogen-associated molecular patterns (PAMP) shared by numerous microorganisms. TLR engagement is involved in innate immunity but also participates in the control of the adaptive immune response, which may be involved in the pathophysiology of allergic diseases like asthma. Experimental studies have largely demonstrated the implication of TLR in both development and control of the allergic reaction. Dendritic cells (DC), which play a key role in these processes, are a privileged target for PAMP. During the allergic reaction, TLR engagement on DC directs the polarization of the T cell response and, while TLR2 and TLR4 may favour both Th1 and Th2 responses, TLR9 induces the development of regulatory T cells.