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Parasites generally have a number of different strategies for avoiding destruction by the immune system of their host: the production of immune regulators, special structural characteristics, and the mimicry of host molecular structures. Unfortunately, the host sometimes contributes to this avoidance by developing ineffective responses. In the case of the parasite Schistosoma mansoni, an infected individual develops an immune response, which is only partially effective. Working with laboratory mice, investigators have now shown that the anti-idiotype network may regulate antibodies to the disadvantage of a host infected with the agent for schistosomiasis mansoni. Idiotypes are the lowest common denominator of antibody molecules; a particular antibody molecule has unique regions which distinguish it from all other antibody molecules, save those which descend from the same original B cell. These unique idiotypes can act as antigens in their own right, and may produce their own immune response. Antibodies directed against the idiotypic region of another antibody molecule are called anti-idiotypes, and they are widely thought to play a role in a complicated network of antibody control. If an antibody has reached the appropriate level in the blood, the production of anti-idiotypes may prevent overproduction. Researchers can experimentally produce anti-idiotypes by injecting stimulated lymphoblasts from another mouse of the same genetic background. When such a mouse, now possessing what researchers have dubbed 'auto-anti-idiotypes', is injected with killed Schistosoma organisms, it fails to mount an adequate immune response. Not only does it fail to produce a normal antibody response, but the response of the cellular immune system to Schistosoma antigens is inadequate as well. These findings suggest that it is not possible to design a vaccine against such parasites without consideration of the anti-idiotypic network of regulation. However, the results also suggest that it may well be possible, by fine-tuning the regulatory network, to produce successful vaccines against organisms which have heretofore been elusive. (Consumer Summary produced by Reliance Medical Information, Inc.)