Basophils, basophilia and helminth infections.

A growing body of evidence suggests basophils are important components of the human immune response to helminth infections. Basophil numbers are increased in several animal models of helminth infection, and basophils have been shown to release both histamine and IL-4 in response to helminths. Helminth infections typically provoke type 2 immune responses characterized by eosinophilia, elevated levels of Ag-specific and polyclonal IgE, and T cell production of type 2 cytokines such as IL-4, IL-5, and IL-13. IL-4 plays a central role in this type 2 response. As basophils are the only peripheral blood mononuclear cells with the ability to release IL-4 rapidly in response to appropriate stimuli, releasing large quantities of preformed IL-4 within minutes of surface IgE cross-linking, it appears likely that basophils play an important role in amplifying ongoing type 2 immune responses to helminth infections once Ag-specific IgE is present. Basophils may also function to initiate type 2 responses upon first exposure to helminths and to potentially re-establish these responses upon re-exposure. This article reviews basic basophil biology and physiology, evaluates the evidence for the presence of basophilia in helminth infections, and then focuses on the possible roles basophils serve in the immune response to helminth infections.