Injection versus infection: the cellular immunology of parasitism

Parasites are immunogenic. But the variety of immune responses they can elicit is matched by their range of mechanisms to evade, subvert or distract these responses. The parasites' aim is survival and reproduction, ours is to restrict or eliminate them, and amplification of protective immune responses has become a key approach to this. But while vaccination has achieved many successes against the 'simpler' organisms such as viruses, the more complex protozoa and helminth parasites have proven much less tractable. In this article, Graham Mitchell discusses the differences between immune responses operated by whole parasites and those induced by prepared fractions.