IgE memory: Persistence of antigen-specific IgE responses years after treatment of human filarial infections

Background: The human immune response to helminth infections is characterized by elevated serum levels of antigen-specific IgE. Although it is well established that IgG Immoral immunity can persist for years, as yet there have been no longitudinal studies of antigen-specific IgE responses to helminth infection in the absence of re-exposure to pathogen. Objective: We sought to determine the presence of filaria-specific IgE responses years after treatment of human filarial infections in patients no longer living in a region endemic for filariasis. Methods: Filaria-specific IgE levels were measured in 34 filaria-infected patients before and I I to 178 (median = 33) months after anthelmintic therapy. Frequencies of filaria-specific IgE-producing cells and measures of filaria-specific IgE-mediated histamine and IL-4 release from basophils were measured in subsets of these patients. Results: At follow-up, all patients were asymptomatic without evidence of active infection, and none had travelled to filaria-endemic regions since initial evaluation. Although frequencies of Brugia malayi antigen (BmAg)-specitic IgE-producing cells and serum levels of BmAg-specific IgE decreased significantly over time, both remained detectable in the majority of patients years after initial treatment. Six of 10 patients' basophils released histamine in response to BmAg after treatment (vs 7 of 10 before treatment). Basophils also continued to release IL-4 after stimulation with BmAg years after treatment. Conclusion: These results demonstrate that filaria-specific IgE production and filaria-specific IgE-mediated basophil release of histamine and IL-4 persist for years after treatment of human filarial infections. Clinical implications: These findings suggest that (1) absolute allergen avoidance may not result in the loss of allergy, and (2) parasite-specific IgE-inducing vaccines, if effective, could potentially induce longstanding protection.