Immunological Studies

Abstract

At the start of the twentieth century, the scientists discarded the possibility of development of acquired immunity in helminth infections as conventional methods of transfer of immune serum or antibodies to susceptible host failed to protect it from subsequent helminth exposure; neither antigen injections protected hosts against subsequent helminth infections. There was also no evidence of killing the helminth or its larval stages, when they were kept in vitro in pool of hyperimmune serum. Slowly, it was learned that hosts do develop acquired immunity against helminths, but its mechanism is different from that known for bacterial and viral infections—a complex phenomenon involving antibodies and antibody-induced cells like eosinophils or mast or other cells which are at play in destroying a helminth. Further, its tegument or digestive enzymes are important targets selected by the host in its fight against helminths. The effects are manifested not only in killing of the helminth but in other ways also that may be their expulsion, affecting egg production, prevention of a stage to develop to next stage or to reach maturity, and affecting sex ratio of the helminth. Even with such conclusive evidences of development of immunity against helminths, it still cannot be confirmed by detecting antibodies which is unlike bacterial and viral immunity. Most of the immunological work on helminths is carried out in laboratory models using schistosomes, Trichinella, and Nippostrongylus species with a few studies in natural infections. This has resulted in coining some new terms which are specific for helminth immunity, i.e., zoo prophylaxis, concominant immunity, self-cure, postparturient rise, etc. There are reviews which deal the subject in greater detail, e.g., Kagan (1966) and Smithers and Terry (1969, 1976).