HOST-PARASITE RELATIONSHIPS OF FASCIOLA HEPATICA IN WHITE MOUSE .2. STUDIES ON ACAUIRED IMMUNITY

Experimental mice were immunized by 2 stimulating infections, each with 2 F. hepatica metacercariae. Afterwards, a challenging infection of the same size was given to them as well as to non-immunized controls. In the experimental mice, there was an earlier migration of the worms from the liver to the common bile duct, and at 40 days after challeng they harbored significantly fewer worms than the controls. Various host measurements (body weight, total and differential leukocyte numbers, spleen weight, hemagglutinating antibody titer, and liver histopathology) indicated a much more rapid response by the experimental animals. On the basis of the nature and timing of lymphocyte infiltration in, and the histopathology of, the livers, it is suggested that delayed (cellular) hypersensitivity may play a prominent role in the earlier migration of worms to the common bile duct.