Chitinolytic activity in nasal polyps

Chitin is a recognition element for tissue infiltration by innate cells implicated in allergy and immunity. This process can be negatively regulated by vertebrate chitinases. Both acidic mammalian chitinase (AMCase) and chitotriosidase (ChT) have chitinolytic activity. This study aimed to determine the activities of AMCase and ChT in nasal polyps (NPs), as well as their in situ localization in NP tissue. AMCase and ChT activities in NPs were compared with those in inferior turbinate tissue samples. Tissue samples were measured for AMCase and ChT activities at a range of pHs using the fluorogenic substrate 4-methylumbelliferyl-beta-d-N,N',N''-triacetyl-chitotriose. Double immunofluorescent staining for the localization of both AMCase and ChT was performed using NP cryosections. Both AMCase and ChT displayed markedly increased chitinolytic activity in all NPs, compared with inferior turbinate tissues. Double immunofluorescent staining revealed that CD68 highlighted monocytes in the submucosa of NP and these cells disclosed coexpression of AMCase and ChT. CD31 detected capillary endothelial cells, but did not express any AMCase and ChT. The increased chitinolytic activities of AMCase and ChT in NPs may be important in NP pathogenesis, suggesting that inhibition of chitinolytic activity may be a novel therapeutic strategy for the treatment of NPs.