Serine protease (PubMed:11893850, PubMed:16436150). Hydrolyzes casein, gelatin and human collagen type IV, but not elastin in vitro (PubMed:16436150). Hydrolyzes OCLN of the human lung epithelial cells at 202-Gln-|-Ser-203 and Gln-211-|-Ile-212 (PubMed:16436150). Inhibited by phenylmethanesulfonyl fluoride (PMSF) and diethyl pyrocarbonate (DEPC), but not by benzamidine. Active at neutral to pH 8 with casein as substrate. Causes an allergic reaction in human. Binds to IgE of patients suffering from bronchial asthma (PubMed:10231324, PubMed:11893850, PubMed:12602675, PubMed:15663570). Binds to IgE in 17% of the 212 asthmatic patients of different age (3 to 94 years old). The binding frequency and intensity to IgE increases significantly with age. Binds also to IgG and IgG4 (PubMed:12602675). Induces histamine release from basophils of asthmatic patients (PubMed:11893850). May contribute to asthma by damaging the barrier formed by the airway epithelium by cleaving the tight junction protein OCLN and stimulating the release of mediators, such as PGE2, CXCL8 and TGFB1, in human respiratory epithelial cells (PubMed:16436150). Belongs to the peptidase S8 family.