The role of chitin and chitinases in innate immunity
Chitin is the second most abundant biopolymer in nature after cellulose and hemicellulose. It is composed of repeated units of N-acetyl-Glucosamine resulting in long chains of parallel or antiparallel chitin, forming nanofibers. This is frequently reinforced by crosslinking with proteins, mineral incrustations, and waxes, giving rise to a panoply of different shapes and functions as diverse as the insect cuticle, insect wings, insect exoskeleton, the fungal cell wall, or helminth eggs.
Neither mammals nor plants contain chitin, as they lack the enzymatic machinery necessary to achieve it synthesis. As chitin is contained in the cell wall of pathogenic fungi, it is probably recognised by the innate immune system as a danger signal. Plants express chitinases in response to fungal infection which are part of Pathogenesis-Related (PR) Proteins Families 3, 4, 8 and 11.
Similarly, mammalian innate immune cells such as macrophages or neutrophilic granulocytes, can secrete de novo synthesised or preformed chitinases. The first human chitinase, known as chitotriosidase or macrophage chitinase (CHIT1) was described by Renkema et al. in 1995 , and a second chitinase called acidic mammalian chitinase (AMCase) was described Boot et al. in the same group in 1999. While AMCase may also have a digestive function, the function of CHIT1 is currently thought to play a role in anti-fungal defense (van Eijk et al. 2005).
We are interested in understanding the roles of human chitinases in innate immunity to fungal or microbial pathogens (Hall et al. 2008) and whether these chitinases can play a protective role in immunity against parasitic worms (Hall et al., 2007). We also collaborate with Maurizio Paoletti and Nicola Manno in Padova who are studying different CHIT1 genotypes in Peruvian indigenous populations with high exposure to chitin via entomophagy and helminth infections.