TLR-2 and IL-17A in chitin-induced macrophage activation and acute inflammation.

Chitin is a ubiquitous polysaccharide in fungi, insects, and parasites. To test the hypothesis that chitin is an important immune modulator, we characterized the ability of chitin fragments to regulate murine macrophage cytokine production in vitro and induce acute inflammation in vivo. In this study, we show that chitin is a size-dependent stimulator of macrophage IL-17A production and IL-17AR expression and demonstrate that these responses are TLR-2 and MyD88-dependent. We further demonstrate that IL-17A pathway activation is an essential event in the stimulation of some but not all chitin-stimulated cytokines and that chitin uses a TLR-2, MyD88-, and IL-17A-dependent mechanism(s) to induce acute inflammation. These studies demonstrate that chitin is a size-dependent pathogen-associated molecular pattern that activates TLR-2 and MyD88 in a novel IL-17A/IL-17AR-based innate immunity pathway.