The induction of immunological tolerance to the parasitic nematode Trichuris muris in cortisone-treated mice.

Tolerance to the parasitic nematode was induced in mice by treatment with cortisone acetate given during the second week of a primary infection, the time at which the host is known to be beginning to respond to the antigens of the parasite. Continuation of the antigenic stimulus provided by infection beyond the period of immunosuppression was an essential requirement for tolerance; if the infection was terminated immediately after treatment the mice remained susceptible to subsequent infection, but then made a primary self-cure response. It is suggested that tolerance involves a long-lasting change in immunological reactivity of the host rather than a paralysis due to an excess of antigen, as tolerance was induced by small infections and persisted for at least 7 weeks in the absence of infection.