A possible role of chitin in the pathogenesis of asthma and allergy.

Chitin is the second most abundant polysaccharide in the world; it is found in insects, parasites and fungi. Chitinases break down chitin, and are a part of the defence mechanism against chitin-containing parasites in lower life forms. This review is based on the results of PubMed-searches using the search-terms: chitin, chitinase, allergy and asthma. Research in murine models has proved that chitin is a size-dependent microbial-associated molecular pattern, with the ability to induce an immunological response via pattern recognition receptors. Medium-sized chitin micro-particles (CMPs) have been shown to induce inflammation, while small-sized CMPs reduce inflammation. The amount of acidic mammalian chitinase correlates with asthma, and the enzyme has been shown to induce chemokine secretion in murine lungs. The high prevalence of asthma among people working with chitinous substances, such as crabs and fungi, supports the hypothesis that chitin might be an allergen playing a role of significance in the development of asthma. This new knowledge about chitin and chitinases, combined with the hygiene-hypothesis, may contribute to a model for the pathogenesis of allergic conditions where chitin and chitinases are potential therapeutic targets.