Immunomodulatory function of chitosan is dependent on complement receptor 3

Chitosan, the deacetylated product of chitin, is a significant component of the cell walls of nearly all fungi. In contrast with the high level of attention paid to plant immune recognition of chitin and chitosan of plant pathogenic fungi we know much less about the mammalian immune system immune recognition of chitosan during infections by human pathogenic fungal species. Here we show that the mammalian β-integrin CR3 complement scavenger receptor, that is expressed on monocytes and macrophages, recognises chitosan from a range of fungal sources and that this leads to the secretion of IL-6, IL-1β and TNF. The secretion of these pro-inflammatory cytokines was dependent on the phagocytosis of chitosan. The co-provision of chitosan along with a peptide (Aspf2 from Aspergillus fumigatus) presented by the MHCII complex potentiated a Th response leading to IL-22 production. Fungal cell wall chitosan therefore activates both the innate and adaptive arms of the human immune system.