Worm recovery, haemagglutinating antibodies and IgE-levels after immunisation against Fasciola hepatica in rats

Female inbred Hooded Lister (HL) rats were each infected with 20 metacercariae (Mc) of Fasciola hepatica. Remarkable variations between the number of flukes established in the bile ducts suggest the presence of individual, perhaps genetically controlled, differences in immune responsiveness of HL rats to F. hepatica. Serum (4 ml) from HL rats infected with 20 Mc 6 weeks prior to transfer partially protected rats against a F. hepatica challenge infection. However, 1 X 10(6) lymphoid cells originating from rats of the same age and stage of infection did not show the same protective qualities. Furthermore, attempts to immunise HL rats i.p. with either juvenile or adult excretory/secretory (ES) products, or somatic tissue antigens and AlOH3-gel as adjuvant failed. When compared to other investigations, the present results further suggest that both the adjuvant and the route of administration are crucial for the stimulation of a protective immunity to F. hepatica. Low titers and low anamnestic responses of haemagglutinating antibodies after prior immunisation with juvenile ES antigens or both juvenile ES and somatic tissue antigen suggest the occurrence of an immunosuppressive effect caused by juvenile ES products. The total serum IgE-levels in immunised groups were generally lower when compared to the challenge control group, whereas the F. hepatica ES-specific IgE-levels rose after challenge, but immediately decreased again when compared to challenge controls. These findings support the hypothesis of an immunomodulatory effect caused by the vaccination scheme.