Helminth-induced immunoregulation: an update

Helminth infections, which have been reduced or eradicated from most developed countries, produce important changes in the immune system. Especially, when chronic and intense, they cause immunosuppression. Although parasites can directly impair health, they may also protect from chronic inflammatory diseases due to induction of immunoregulatory mechanisms, such as regulatory-B and -T cell development which inhibit proliferation of auto-reactive and allergen-specific clones. Innate immune system modulation has also been recognized, highlighting that, besides increasing the number of cells involved in parasite clearance, they also may use them as a target for evasion mechanisms. Some cells, important in the defense against bacteria and other pathogens, also respond to helminths, but with a genetic program highly different from the type-1 classical profile. Parallel to immunosuppression, helminthiasis induce strong type 2 responses in the host; thus, it becomes a concern the situation of some human populations living in places where they are partially controlled, then, slight infection/re-infection cycles prevail and immunosuppression is rather not observed. Ascaris lumbricoides, the most common helminthiasis in the planet, is one of the least studied in terms of immunoregulation and also the most frequently associated to asthma and other allergic conditions