Helminth anti-oxidant enzymes: a protective mechanism against host oxidants?

Highly reactive oxygen species potentially represent a powerful effector mechanism against parasites. They are produced during normal cellular metabolism, especially by activated phagocytes, and also by some anti parasitic drugs. From studies to date, all protozoan and helminth parasites appear to have one or more anti-oxidant enzymes able to scavenge or quench the reactive oxygen species, and there is strong evidence that such enzymes play a crucial role in protecting against the host response. This detailed review, which summarizes studies on the major anti-oxidant enzymes of helminths, clearly illustrates that methods to block or overcome anti-oxidant protection may be a fertile field in the search for improved ways to inhibit parasite survival.