Immunology of human helminth infection.

Parasitic helminths cause enormous morbidity among humans especially in developing countries. These large extracellular organisms have complex life cycles frequently involving an arthropod vector. Helminth parasites can be tissue dwelling or intestinal but all induce a dramatic expansion of the Th2 lymphocyte subset. It remains unclear whether these Th2-derived responses, including IgE, eosinophilia and mastocytosis are important in the protective immune response to the parasite, or are responsible for immune-mediated pathology, or both. Interestingly, despite high levels of IgE and other features of Th2 cell activation, allergic responses are rarely observed in infected individuals. Helminths can survive for years in the infected host, and have evolved elaborate immune evasion strategies to establish these long-lived infections including the induction of tolerance to parasite antigens. This review discusses the dynamics of infection with helminth parasites with specific emphasis on Th2 subset activation. The current knowledge of immune effector mechanisms, immunopathology and hopes for vaccine development are also discussed.