Pattern recognition receptors on mast cells

The Toll-like receptors (TLRs) fit the definition of pattern-recognition molecules, which were originally postulated to allow the innate immune system to detect the 'molecular signatures' of various infectious agents. Although the innate immune system has no memory, it shows a degree of specificity, in part because the various TLRs recognize different sets of pathogen-associated molecules. Dermal mast cells are usually associated, not with the innate immune system, but with atopic dermatitis, but Supajatura et al. have found that these cells also express TLRs. They report here that TLR4, which binds the gram-negative product lipopolysaccharide (LPS), and TLR2, which binds peptidoglycan (PGN) from gram-positive organisms like Staphylococcus aureus, induce distinct mast cell responses. Staphylococcus is known to exacerbate allergic dermatitis, but it has generally been thought to act by inducing antibacterial IgE's, which trigger mast cell degranulation by stimulating the IgE receptor. Interestingly, the authors show that the interaction between PGN and TLR2 can provoke mast cell degranulation directly, sidestepping the need for IgE receptor engagement.

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