Pepsin-digested peanut contains T-cell epitopes but no IgE epitopes.
BACKGROUND: Peanuts are a common cause of food-induced anaphylaxis and fatalities. Previous studies have demonstrated that rush immunotherapy to crude peanut extract reduces clinical symptoms triggered by oral peanut challenges, but the immunotherapy was associated with an unacceptably high incidence of systemic allergic reactions. One approach to reduce the frequency of allergic reactions would be to use a modified peanut antigen with low allergenic properties. OBJECTIVE: We sought to determine the immunologic characteristics of crude intact peanut extract before and after pepsin digestion. METHODS: We used IgE immunoblotting and assessment of T-lymphocyte responses to intact and peptic digests of peanut extracts. RESULTS: Western blot analysis of sera from 5 subjects with peanut allergy showed multiple IgE-reactive proteins in crude intact peanut extract that were eliminated after pepsin treatment of the peanut extract. In contrast, pepsin-digested peanut induced significant T-cell proliferation responses (stimulation index = 30) in vitro in PBMCs from 7 subjects with peanut allergy, albeit at lower levels than that induced by intact peanut (stimulation index = 66). Furthermore, IFN-gamma production was induced by intact peanut and pepsin-digested peanut in a concentration-dependent manner. Importantly, T-cell lines generated in response to intact peanut also reacted to pepsin-digested peanut, indicating cross-reactive T-cell epitopes in intact and pepsin-digested peanut. CONCLUSION: These findings suggest that pepsin-digested peanut may be useful in peanut immunotherapy because pepsin digestion eliminates IgE reactivity but maintains T-cell reactivity.