How parasites evade the immune response

Infections caused by parasitic protozoa and worms are characteristically longlasting, 40-60 years in some forms of malaria and Chagas' disease for example. For years many parasitologists believed that there was no effective immunity against most parasites, but the prevalence of exacerbated or disseminated infections in immunosuppressed patients altered this viewpoint. It is now widely accepted that acquired immunity is the rule but that the parasites escape its consequences by actively evading the immune response. This evasion has important consequences because on one hand it is the cause of the immunopathology that does the real damage in most infections and on the other it places a major constraint on the development of vaccines. It was against this background that a recent symposium considered the immunological basis of the evasion of the immune response(∗).