title: Chitosan but not chitin activates the inflammasome by a mechanism dependent upon phagocytosis.
abstract: Chitin is an abundant polysaccharide found in fungal cell walls, crustacean shells, and insect exoskeletons. The immunological properties of both chitin and its deacetylated derivative chitosan are of relevance because of frequent natural exposure and their use in medical applications. Depending on the preparation studied and the end point measured, these compounds have been reported to induce allergic responses, inflammatory responses, or no response at all. We prepared highly purified chitosan and chitin and examined the capacity of these glycans to stimulate murine macrophages to release the inflammasome-associated cytokine IL-1β. We found that although chitosan was a potent NLRP3 inflammasome activator, acetylation of the chitosan to chitin resulted in a near total loss of activity. The size of the chitosan particles played an important role, with small particles eliciting the greatest activity. An inverse relationship between size and stimulatory activity was demonstrated using chitosan passed through size exclusion filters as well as with chitosan-coated beads of defined size. Partial digestion of chitosan with pepsin resulted in a larger fraction of small phagocytosable particles and more potent inflammasome activity. Inhibition of phagocytosis with cytochalasin D abolished the IL-1β stimulatory activity of chitosan, offering an explanation for why the largest particles were nearly devoid of activity. Thus, the deacetylated polysaccharide chitosan potently activates the NLRP3 inflammasome in a phagocytosis-dependent manner. In contrast, chitin is relatively inert.
authors.affiliation: Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605.
authors.forename: Chelsea L
authors.initials: CL
authors.lastname: Bueter
authors.affiliation: Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605.
authors.forename: Chrono K
authors.initials: CK
authors.lastname: Lee
authors.affiliation: Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, Worcester, Massachusetts 01605.
authors.forename: Vijay A K
authors.initials: VAK
authors.lastname: Rathinam
authors.affiliation: New England Biolabs, Inc., Ipswich, Massachusetts 01938.
authors.forename: Gloria J
authors.initials: GJ
authors.lastname: Healy
authors.affiliation: New England Biolabs, Inc., Ipswich, Massachusetts 01938.
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Taron
authors.affiliation: Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Specht
authors.affiliation: Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605. Electronic address: stuart.levitz@umassmed.edu.
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Levitz
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D002686:Chitin / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology*; D048271:Chitosan / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology*; D015638:Cytochalasin D / Q000494:pharmacology; D006490:Hemostatics / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D058847:Inflammasomes / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects* / Q000276:immunology; D013329:Structure-Activity Relationship
chemical_list: D002352:Carrier Proteins; D006490:Hemostatics; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D019384:Nucleic Acid Synthesis Inhibitors; D002686:Chitin; D015638:Cytochalasin D; D048271:Chitosan