PT  - JOURNAL ARTICLE
AU  - Tzu-Hsuan Chang
AU  - Yamel Cardona Gloria
AU  - Margareta J. Hellmann
AU  - Carsten Leo Greve
AU  - Didier Le Roy
AU  - Thierry Roger
AU  - Lydia Kasper
AU  - Bernhard Hube
AU  - Stefan Pusch
AU  - Neil Gow
AU  - Morten Sørlie
AU  - Anne Tøndervik
AU  - Bruno M. Moerschbacher
AU  - Alexander N.R. Weber
TI  - Transkingdom mechanism of MAMP generation by chitotriosidase (CHIT1) feeds oligomeric chitin from fungal pathogens and allergens into TLR2-mediated innate immune sensing
AID  - 10.1101/2022.02.17.479713
DP  - 2022 Jan 01
TA  - bioRxiv
PG  - 2022.02.17.479713
4099  - http://biorxiv.org/content/early/2022/02/19/2022.02.17.479713.short
4100  - http://biorxiv.org/content/early/2022/02/19/2022.02.17.479713.full
AB  - Chitin is a highly abundant polysaccharide in nature and linked to immune recognition of fungal infections and asthma in humans. Ubiquitous in fungi and insects, chitin is absent in mammals and plants and, thus, represents a microbe-associated molecular pattern (MAMP). However, the highly polymeric chitin is insoluble, which potentially hampers recognition by host immune sensors. In plants, secreted chitinases degrade polymeric chitin into diffusible oligomers, which are ‘fed to’ innate immune receptors and co-receptors. In human and murine immune cells, a similar enzymatic activity was shown for human chitotriosidase (CHIT1) and oligomeric chitin is sensed via an innate immune receptor, Toll-like receptor (TLR) 2. However, a complete system of generating MAMPs from chitin and feeding them into a specific receptor/co-receptor-aided sensing mechanism has remained unknown in mammals. Here, we show that the secreted chitinolytic host enzyme, CHIT1, converts inert polymeric chitin into diffusible oligomers that can be sensed by TLR1-TLR2 co-receptor/receptor heterodimers, a process promoted by the lipopolysaccharide binding protein (LBP) and CD14. Furthermore, we observed that Chit1 is induced via the β-glucan receptor Dectin-1 upon direct contact of immortalized human macrophages to the fungal pathogen Candida albicans, whereas the defined fungal secreted aspartyl proteases, Sap2 and Sap6, from C. albicans were able to degrade CHIT1 in vitro. Our study shows the existence of an inducible system of MAMP generation in the human host that enables contact-independent immune activation by diffusible MAMP ligands with striking similarity to the plant kingdom. Moreover, this study highlights CHIT1 as a potential therapeutic target for TLR2-mediated inflammatory processes that are fueled by oligomeric chitin.Competing Interest StatementThe authors have declared no competing interest.