Fasciola hepatica in rats: transfer of immunity by serum and cells from infected to F. hepatica naive animals.

Immune, hyperimmune, and nonimmune serum samples were collected from inbred rats following 10 to 15 weeks of one [5 metacercariae (mc)/rat], two (5 mc followed by 30 mc/rat) or no (uninfected) exposure to Fasciola hepatica. Lymphoid cells also were collected from these donors. Inbred, naive rats in groups receiving immune serum, hyperimmune serum, nonimmune serum (serum control), immune cells, hyperimmune cells, and nonimmune cells (cell control) received intraperitoneally either a total of 20 ml of serum or a total of 3 x 10(8) viable lymphoid cells. A challenge infection of 30 mc/rat was administered orally at about the time of serum or cell transfer. The transfer of immunity was evaluated by examining recipient rats for parasites 4 and 8 weeks after challenge. Some hematological parameters and the precipitating antibody response of the recipients were monitored also. Hyperimmune serum, unlike immune serum, consistently provided a significant degree of protection in recipient rats. The precipitating antibody titre of this serum was higher than that obtained from the immune donor group. The importance of a second sensitization to obtain sufficiently potent serum was demonstrated. Lymphoid cells from infected donors did not consistently confer protection on recipients. Thus, the expression of protective immunity against F. hepatica seemed to be more dependent on the presence of antibodies than on cells. The hematological parameters of the recipients, in general, supported this observation. The precipitating-antibody response of protected rats was lower than that of unprotected animals following challenge, presumably because the development of fewer worms in the former provided less antigenic stimulation.