Immune modulation by the helminth parasite Fasciola hepatica

Abstract

The incidence of allergic and autoimmune disease In the developed world has Increased dramatically In the past century. This has coincided with a reduction In the Incidence of infectious disease. The hygiene hypothesis suggests that reduced exposure to Infectious organisms, and in particular parasitic worms (helminths), has led to disordered regulation of the Immune system, and hence to an increase In these inflammatory disorders. Infection with parasitic helminths induces polarised Th2 Immune responses but this is largely Ineffective at clearing the parasite. Indeed, the host remains remarkably tolerant to helminths. There is a growing consensus that the host and parasite work In tandem to mediate this effect, with the helminth benefiting through survival, while the host benefits from not mounting destructive inflammatory reactions. Host immunity to helminths has thus developed, perhaps through co-evolutlon with helminths, to limit pathology and to balance immune resistance with susceptibility and immune pathology.