Molecular characterization of a novel Trichinella spiralis aspartyl protease and its role in the larval invasion of host intestinal epithelial cells.

The aim of the present study was to characterize the molecular properties of a novel Trichinella spiralis aspartic protease (TsEasp) and to investigate its role in the larval invasion of host intestinal epithelial cells. The full-length TsEasp cDNA was cloned and expressed, and recombinant TsEasp protein (rTsEasp) was purified. Immunization of mice with rTsEasp elicited a robust specific IgG response. qPCR analyses revealed that TsEasp was transcribed at all T. spiralis developmental stages, with markedly higher transcription levels in intestinal infective larvae and adult worms. Indirect immunofluorescence testing showed that TsEasp was expressed throughout the T. spiralis life cycle, and mainly localized at the cuticle, and embryonic periphery in adult females. Far-western blot and indirect immunofluorescence confirmed that rTsEasp binds specifically to Caco-2 cells, predominantly on the cell membrane. The in vitro invasion assay showed that rTsEasp significantly accelerated the larval invasion of Caco-2 monolayers in a dose-dependent manner of rTsEasp protein, whereas anti-rTsEasp antibodies and RNAi markedly suppressed this invasion. Collectively, our results indicate that TsEasp is a key invasive virulence factor in T. spiralis infection.