An Aspartyl Protease Inhibitor Orthologue Expressed by Parelaphostrongylus tenuis Is Immunogenic in an Atypical Host

Abstract

ABSTRACT Parelaphostrongylus tenuis is a neurotropic nematode common in white-tailed deer ( Odocoileus virginianus ) of eastern North America. This parasite is the causative agent of a debilitating neurologic disease in atypical hosts, including domestic livestock. In order to identify proteins of potential significance in the host-parasite relationship, a cDNA library was produced from adult P. tenuis mRNA. Screening the library with antisera from infected red deer ( Cervus elaphus elaphus ) and immunized AO strain rats, we identified clones with sequence similarities to aspartyl protease inhibitors from several parasitic nematodes. Antibody that was generated against this recombinant protein of P. tenuis ( Pt -API-1) detected the native protein in E/S products, in muscle and gonad, and on the surface of the cuticle of adult male and female P. tenuis . The native protein was detected in internal structures of first-stage (L1) and third-stage (L3) larvae. Reverse transcription-PCR confirmed expression of Pt - api-1 in L1, L3, and adult male and female worms. Expression of Pt -API-1 throughout the life cycle of P. tenuis suggests an essential function. Antibodies specific for recombinant Pt -API-1 were detected by enzyme-linked immunosorbent assay in sera from 12 red deer experimentally infected with P. tenuis . Antibodies were detected within 28 to 56 days postinfection. Responses were sustained or biphasic in animals with patent infections, consistent with expression of Pt -API-1 by L1. Our results are compatible with findings in other parasitic nematodes showing that aspartyl protease inhibitors are highly immunogenic.