SOME IMMUNOLOGIC ASPECTS OF PARASITIC HELMINTH INFECTIONS

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Abstract
Studies on the host-parasite relationship of the sheep stomach worm, Haemonchus contortus suggest that important antigens which are involved in the stimulation of immunologic resistance are released during growth and development of the parasite as it penetrates, molts, and matures in the host. These antigens seem to be released and made available to the host for only short periods of time and in some instances may be present for only a few minutes. Because nematodes do not undergo multiplication in host tissues and because the rate of acquisition of parasites and their subsequent development in the host is irregular, it is difficult regularly to elicit good levels of immunologic resistance by infection procedures which utilize normal or attenuated infective larvae. The recent development of techniques for in vitro maintenance and cultivation of various parasitic stages of the parasite provide a means for collecting antigens elaborated during growth and ecdysis. Results with these materials give hope that it might be feasible to induce an immune resistance response by vaccination which in some cases may be better than that resulting flora natural infection.