Serpin expression in the parasitic stages of Trichostrongylus vitrinus, an ovine intestinal nematode

Abstract

Members of the genus Trichostrongylus, such as T. vitrinus, being endemic in Northern Europe, are among the principal causative nematodes which contribute to parasitic gastro-enteritis in sheep world-wide, inhabiting the proximal small intestine and causing damage to the mucosa. This results in impaired nutrient absorption as well as a pronounced inflammatory response with cellular infiltration of the mucosa, including a pronounced mast cell response. These mast cells release serine proteinases that enhance the passage of effector cells and macromolecules across epithelial boundaries and into direct contact with the invading parasite. The adult and larval stages of T. vitrinus release a number of serine proteinases in vitro that may contribute to tissue invasion and nutrient acquisition in vivo. This study describes the molecular cloning and characterization of a serine proteinase inhibitor (serpin) that is present in extracts of all the parasitic stages, becoming more abundant as the life-cycle progresses. The serpin is present in the in vitro excretory/secretory products (ES) of 4th-stage larval and adult parasites, being more abundant in the former. The serpin was expressed in E. coli and the recombinant protein was a potent inhibitor of several host serine proteinases including mast cell proteinases. The serpin may regulate the activity of the parasite serine proteinases or it may modulate the host immune response to the parasite by inhibiting the activity of serine proteinases released from host inflammatory cells.