T cell Regulation and the Control of Helminth Infections
Helminth infections are among the most neglected communicable diseases afflicting developing countries. Pharmacological treatments are compromised by rapid re-infection, variable compliance, and emerging resistance. Vaccination has not yet succeeded in evoking strong resistance. The critical barrier in helminth control remains the failure of the immune system to clear parasites despite antigen recognition. Addressing the fundamental question of why the immune system is restrained from killing parasites, will offer a novel route for intervention to achieve an immunological cure.
Recent developments in immunology offer a conceptual framework to understand the failure of immunity and suggest how to restore the full potential of our defence mechanisms. In this model, parasites induce regulatory T cell populations, which suppress anti-parasite effector cells, as part of the parasites own strategy for survival in the host. Because regulatory T cells are stimulated by parasite antigens, repeated infection or vaccination will induce a modest immune response, but fall short at the critical effector cell level required for parasite killing. Only by inactivating or removing the regulatory T cells can the immune response display its full capability to eliminate the parasites.
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