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 i mportant source of allergens, which can cause allergic conditions. The cyst eine protease activity of Der p 1 may enhance the potency of this major mit e allergen through cleavage of CD23 and CD25 from the surface of immune cel ls, IgE independent mast cell activation, increases in epithelial cell perm eability and inactivation of an endogenous serine protease inhibitor. Inhib ition 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 in hibitor, in a range of assays that directly or indirectly measure Der p 1 p rotease activity and to compare its activity to endogenous cysteine proteas e inhibitors. Methods The proteolytic activities of purified Der p 1 or HDM extract and i nhibitory properties of PTL11028 were examined through cleavage of an artif icial peptidyl substrate, cleavage of CD23 from human B cells and permeabil ity studies on primary human bronchial epithelial cells. Results PTL11028 is a highly potent and specific Der p 1 inhibitor, being e ffective against both purified protease and Der p 1 within HDM extract. PTL 11028 can completely inhibit Der p 1-mediated CD23 cleavage from human B ce lls and also reduces HDM-induced human bronchial epithelial cell permeabili ty by 50%. Der p 1 is potently inhibited by cystatin A and to a lesser exte nt 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 modu lated in vivo by some human cystatins. PTL11028 prevents the Der p 1-mediat ed cleavage of CD23 from human B cells and significantly reduces HDM-induce d 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.