Strongyloides ratti: formation of protection in rats by excretory/secretory products of adult worms.

Formation of a marked protective immunity against the challenge infection was found in the rats immunized with excretory/secretory (ES) products of Strongyloides ratti adult worms. Immunization by intraduodenal injection of ES products reduced both the fecal egg counts and the adult worm burden by subcutaneous inoculation of infective larvae and by an intraduodenal implantation. The duration of parasitism in the immunized rats, however, was not shortened compared with that of control rats. The normal migration of subcutaneously challenged larvae was not affected by ES product immunization. Intestinal mastocytosis occurred according to the appearance of adult worms in the small intestine of the immunized rats earlier than it did in controls. This result suggests that mastocytosis is involved in the induction of protection by ES products of S. ratti adult worms.