Commensal House Dust Mite Allergen in Human Gut: A Contributor to Gut Inflammatory Disease in Humans?

Introduction: Recently we have demonstrated that neonatal gut can be directly exposed to the respiratory allergen house-dust-mite (HDM) allergen (Dermatophagoides pteronyssinus, Der p1) through breast-milk. Currently, there is no evidence for presence of a respiratory allergen in the human gut or its possible impact on gut inflammation. Aim: To explore the direct effect of HDM on healthy gut mucosal function. Methods: Colonic biopsies (n=30) and duodenal fluid (n=28) were taken from healthy adults undergoing routine colonoscopy. Stool was obtained from healthy volunteers (n=10). Der p1 was measured in duodenal and stool samples by ELISA. Direct effect of HDM (0.1-100 ng/ml) was assessed on tissue resistance, ex vivo paracellular permeability, ZO-1 and occludin tight-junction protein expression by immunostaining, and cytokine production in cultured colon (TNF-alpha and IL-10). Permeability and cytokine production was examined in presence or absence of cysteine- (E-64, 10 mM), serine- (AEBSF, 1 mM) or non-selective (chymostatin, 10 mg/ml) protease-inhibitors. Results: Derp1 was present in duodenal and stool samples. HDM induced a dose-dependent increase in gut paracellular permeability, TNF-alpha and IL-10 productionand a reduction in tissue resistance (P<0.001). This was associated with reduced expression of ZO-1 and occludin immunostaining in colonic sections (P<0.01). HDM-induced permeability and cytokine production was significantly abolished by chymostatin and E-64 (P<0.001) but not AEBSF. Conclusion: HDM is present in human gut mucosa. It directly impairs the gut barrier function. These effects are cysteine-protease dependent. These novel results warrant further studies to explore the potential contribution of HDM to pathophysiology of gut inflammatory diseases.