Chitinase-like proteins as regulators of innate immunity and tissue repair: helpful lessons for asthma?

Chitinases and chitinase-like proteins (CLPs) belong to the glycoside hydrolase 18 (GH18) family of proteins. Chitinases are expressed in mammals and lower organisms and facilitate chitin degradation, hence act as host-defence enzymes. Gene duplication and loss-of-function mutations of enzymatically active chitinases has resulted in the expression of a diverse range of CLPs across different species. CLPs are genes that are increasingly associated with inflammation and tissue remodelling, not only in mammals but also across distant species. Whilst the focus has remained on understanding the functions and expression patterns of CLPs during disease in humans, studies in mouse and lower organisms have revealed important and overlapping roles of the CLP family during physiology, host-defence and pathology. This review will summarise recent insights into the regulatory functions of CLPs on innateimmune pathways and discuss how these effects are not only important for host-defence and tissue injury/repair after pathogen invasion, but also how they have extensive implications for pathological processes involved in diseases such as asthma.