Immunity in Mammals to Helminths of the Circulatory and Lymphatic Systems, Emphasizing Nonhuman Primate Models and Their Comparison to Human Infections and Rodent Models

The host—parasite relationship of intravascular helminthsin mammalian hosts is complex, consisting of several interrelatedaspects. These organisms are often very long lived in thesehosts that possess highly evolved immune systems, which impliesthe existence of mechanisms in these complex parasites for evadingthe immune response. On the other hand, mammalian hosts appearto be very successful in limiting their worm burdens, mainlyby preventing reinfection. Thus, a balance between host andparasite is often achieved. This balance extends to the immunopathologicalconsequences of the infections as well. Especially in the schistosomes,where relatively more is known about immunopathology, it isbecoming increasingly apparent that immunopathological reactionsto the eggs are multifunctional and paradoxical: they causedisease, they limit disease, and they even serve the schistosomeby making possible the escape of its eggs, laid deep withinthe tissues, from the host's body to propagate the life cycle.The comparative approach, using different species of schistosomesand filarids in different mammalian hosts, has proved to bevaluable for understanding the immunological basis of thesecomplex relationships. The knowledge gained from these modelsystems is already being vigorously applied to the human diseases,two of the great scourges of the tropics, schistosomiasis andlymphatic filariasis, to the end of their eradication from theearth by mass immunization.