Functional effects of the inhibition of the cysteine protease activity of the major house dust mite allergen Der p 1 by a novel peptide-based inhibitor.

BACKGROUND: The house dust mite (HDM) Dermatophagoides pteronyssinus is an important source of allergens, which can cause allergic conditions. The cysteine protease activity of Der p 1 may enhance the potency of this major mite allergen through cleavage of CD23 and CD25 from the surface of immune cells, IgE independent mast cell activation, increases in epithelial cell permeability and inactivation of an endogenous serine protease inhibitor. Inhibition of the enzymatic activity of Der p 1 may therefore be of therapeutic benefit.
OBJECTIVE: To examine the activity of PTL11028, a newly developed Der p 1 inhibitor, in a range of assays that directly or indirectly measure Der p 1 protease activity and to compare its activity to endogenous cysteine protease inhibitors.
METHODS: The proteolytic activities of purified Der p 1 or HDM extract and inhibitory properties of PTL11028 were examined through cleavage of an artificial peptidyl substrate, cleavage of CD23 from human B cells and permeability studies on primary human bronchial epithelial cells.
RESULTS: PTL11028 is a highly potent and specific Der p 1 inhibitor, being effective against both purified protease and Der p 1 within HDM extract. PTL11028 can completely inhibit Der p 1-mediated CD23 cleavage from human B cells and also reduces HDM-induced human bronchial epithelial cell permeability by 50%. Der p 1 is potently inhibited by cystatin A and to a lesser extent by cystatins C and E/M.
CONCLUSION: PTL11028 is a highly potent and selective irreversible inhibitor of the cysteine protease activity of Der p 1, an activity that may be modulated in vivo by some human cystatins. PTL11028 prevents the Der p 1-mediated cleavage of CD23 from human B cells and significantly reduces HDM-induced permeabilization of the epithelial barrier. PTL11028 is an important tool to examine the biological effects of Der p 1 in a range of in vitro and in vivo model systems.