Abstract
The injection of cell-free extracts of larval Trichinella spiralis with Freund complete adjuvant immunized rats against a challenge infection with T. spiralis. Protection was expressed by a reduction of adult worms in the intestines 8 days after a challenge infection. The quantitatively more important rapid expulsion reaction could also be produced by immunization with antigen, provided immunized rats were also given an intestinal priming infection with adult Trichinella spiralis or an unrelated nematode, Heligmosomoides polygyrus. These parasites stimulated a local change in the intestine that synergistically interacted with immunity to give up to 90% protection through the rapid expulsion response. Intestinal priming had to follow antigen administration by not less than 5 days and was optimal when 10 days elapsed. These experiments provide evidence for an immunological component in the rapid expulsion process. In addition, the technique suggests that the utilization of intestinal priming may provide a new approach for the development of intestinal antihelminth vaccines.