The transmembrane protein occludin of epithelial tight junctions is a functional target for serine peptidases from faecal pellets of Dermatophagoidespteronyssinus

Background There have been only a few studies of how allergens cross the ai rway epithelium to cause allergic sensitization. House dust mite fecal pell ets (HDMFP) contain several proteolytic enzymes. Group I allergens are cyst eine peptidases, whilst those of groups 3, 6 and 9 have catalytic sites ind icative of enzymes that mechanistically behave as serine peptidases. We hav e previously shown that the group 1 allergen Der p 1 leads to cleavage of t ight junctions (TJs), allowing allergen delivery to antigen presenting cell s. Objective In this study we determined whether HDMFP serine peptidases simil arly compromise the airway epithelium by attacking TJs, desmosomes and adhe rens junctions. Methods Experiments were performed in monolayers of MDCK, Calu-3 or 16HBE14 o-epithelial cells. Cell junction morphology was examined by 2-photon molec ular excitation microscopy and digital image analysis. Barrier function was measured as mannitol permeability. Cleavage of cell adhesion proteins was studied by immunoblotting and mass spectrometry. Results HDMFP serine peptidases led to a progressive cleavage of TJs and in creased epithelial permeability. Desmosomal puncta became more concentrated . Cleavage of TJs involved proteolysis of the TJ proteins, occludin and ZO- 1. This was associated with activation of intracellular proteolysis of ZO-1 . In contrast to occludin, E-cadherin of adherens junctions was cleaved les s extensively. Although Calu-3 and 16HBE14o-cells expressed tethered ligand receptors for serine peptidases, these were not responsible for transducin g the changes in TJs. Conclusion HDMFP serine peptidases cause cleavage of TJs. This study identi fies a second general class of HDM peptidase capable of increasing epitheli al permeability and thereby creating conditions that would favour transepit helial delivery of allergens.