A NOVEL EX-VIVO RAT INFECTION MODEL TO STUDY PROTECTIVE IMMUNITY AGAINST FASCIOLA-HEPATICA AT THE GUT LEVEL

We describe an ex vivo rat infection model to study protective immunit y against Fasciola hepatica at the gut level. An exact number of newly excysted juveniles (NEJs) was injected into a gut segment with an int act blood supply and which was still attached to a live anaesthetized rat. NEJs that penetrated the gut wall during the following 6 h were r ecovered from a beaker filled with medium and were counted under a mic roscope. This infection model was validated and enabled us to exactly quantify the infection dose whilst at the same time exactly quantifyin g the number of NEJs penetrating the gut wall. The mean sum of NEJs th at migrated through the gut wall into the beaker (peritoneal fraction) , plus NEJs that remained in the gut wall and the gut lumen was 87% of the infective dose (+/- 3.6% SEM; n = 18). The function of the ex viv o segments was well-preserved, as demonstrated by only minor leakage o f an inert liquid marker. The ex vivo model enabled us to measure prot ection against F. hepatica at the gut level. In naive rats 52% (+/-2.4 % SEM; n = 40) of the injected NEJs penetrated the gut wall, whereas i n previously infected rats only 12% (+/-1.8% SEM; n = 40) were able to do so, irrespective of the infection dose. Thus, when rats were orall y primed, the migration of NEJs through the gut wall was 77% less than the migration in naive rats. We conclude that the ex vivo model shoul d be valuable in studies of the induction and expression of protective immunity against F, hepatica in the intestine, and will aid in develo pment and optimization of vaccines. (C) 1998 Elsevier Science B.V. All rights reserved.