A cysteine protease from Spirometra erinaceieuropaei plerocercoid is a critical factor for host tissue invasion and migration

Sparganosis in humans caused by the plerocercoid larvae of Spirometra erinaceieuropaei is found worldwide, especially in Eastern Asia and the Far East. Previous studies have suggested that dissolution of plerocercoid body, plerocercoid invasion of host tissue, and migration are important processes for sparganosis progression. However, the mechanisms underlying these processes have yet to be determined. Here, we demonstrated the enzymatic property and involvement of a native 23kDa cysteine protease (Se23kCP), purified from plerocercoids, in sparganosis pathogenesis. Se23kCP is mature protease consisting of 216 amino acids and has a high sequence similarity with cathepsin L in various organisms. Se23kCP conjugated with N-glycans, which have a core fucose residue. Both cysteine and serine protease-specific activities were determined in Se23kCP and their optimal pHs were found to be different, indicating that Se23kCP has a wide range of substrate specificity. Se23kCP was secreted from tegumental vacuoles of the plerocercoid to host subcutaneous tissues and degraded human structural proteins, such as collagen and fibronectin. In addition, the plerocercoid body was lysed by Se23kCP, which facilitated larval invasion of host tissue. Our findings suggest that Se23kCP induces host tissue invasion and migration, and might be an essential molecule for sparganosis onset and progression.