Effects on Trichinella spiralis of host responses to purified antigens.

Purification of two antigens (48-kilodalton polypeptide and a group with major subunits of 50 and 55 kilodaltons) from the infective larvae of the parasitic nematode Trichinella spiralis was recently reported. Immunization of mice with either of these antigens induces strong resistance to a subsequent challenge infection. In the study reported here the mechanism of this resistance was investigated by monitoring the parasite's life cycle in mice immunized with the antigens. Immunized mice were able to expel intestinal adult worms and to inhibit the fecundity of adult female worms at an accelerated rate compared to control mice. Accelerated expulsion and inhibition of fecundity may account entirely for the level of resistance induced by immunization. Although the effects of the immune response apparently are exerted on adult worms, the target antigens are expressed only by developing larvae. This suggests that immune effector mechanisms act on intestinal larvae in such a way that they develop into defective adults.