LOCATION OF INDUCTION AND EXPRESSION OF PROTECTIVE IMMUNITY AGAINST FASCIOLA-HEPATICA AT THE GUT LEVEL - A STUDY USING AN EX-VIVO INFECTIONMODEL WITH LIGATED GUT SEGMENTS

In the present study, we investigated the site in the host where prote ctive gut immunity to Fasciola hepatica is induced and expressed, foll owing the infection route of the parasite. Expression of protection wa s studied in ex vivo gut segments with intact blood and lymph supply t hat were prepared at different locations along the entire length of th e small and large intestine. Four weeks after oral infection, signific ant protection was detected in the duodenum, upper jejunum, midjejunum , and ileum. Protection at the gut level was expressed as early as 2 w k after oral priming and waned after 27 wk. The possibility that the g ut wall plays a role in age-related protection was excluded. The effec t of newly excysted juveniles (NEJ) penetrating the gut on the inducti on of protection was studied by recovering or killing the NEJs of the primary infection immediately after gut migration. Results showed that protection was low (13.9-19.8%). However, when gut migration was by-p assed and NEJs of the primary infection were injected into the periton eal cavity or between the liver lobes, high levels of protection at th e gut level were detected (76.5-87.4%). The results indicate that prot ection expressed at the gut level is induced by the parasite at a youn g stage, during migration through the peritoneal cavity, or liver, or both and not during penetration of the gut.