Immunomodulation by helminthic parasites and worm therapy.

The helminthic parasites have largely been looked upon as chronic infections in developing countries causing morbidity. The helminthic parasites, unlike other microbial pathogens, are unique in the way they interact with the host's immune system. Their size, complexity, and movement within the host trigger the host's immune response toward a relative state of hyporesponsiveness, favoring cohabitation. This immunomodulation has been a topic of much debate in the last decade. This review explicitly explains how helminthic parasites are capable of modulating the host's immune system and how this immunomodulation is brought about at different stages of immune activation. The proven and postulated mechanisms of altered antigen presentation and activation of both arms of the immune system, cell-mediated and humoral, are presented. The review further summarizes what effect this immunomodulation has on bystander immune responses and how the presence of helminthic parasites can contribute to alleviating immune-dysregulation conditions in the host. An updated account of the current usage of "worm therapy" in different autoimmune diseases, allergic conditions, and even cancer therapy is presented.