Natural human Bet v 1‐specific IgG antibodies recognize non‐conformational epitopes whereas IgE reacts with conformational epitopes
Georgii Brazhnikov, Evgenii Smolnikov, Alla O. Litovkina, Tianchi Jiang, Artem Shatilov, Inna Tulaeva, Mikhail Tulaev, А. В. Караулов, Alina Poroshina, Yury V. Zhernov, Margarete Focke‐Tejkl, Milena Weber, Oluwatoyin Akinfenwa, O G Elisyutina, Sergey Andreev, I.P. Shilovskiy, Nadezda N. Shershakova, Smirnov Vv, E S Fedenko, T. S. Lepeshkova, Е. К. Beltyukov, В. В. Наумова, Michael Kundi, Musa Khaitov, Ursula Wiedermann, Rudolf Valenta, Raffaela Campana
Abstract
BACKGROUND: The nature of epitopes on Bet v 1 recognized by natural IgG antibodies of birch pollen allergic patients and birch pollen-exposed but non-sensitized subjects has not been studied in detail. OBJECTIVE: To investigate IgE and IgG recognition of Bet v 1 and to study the effects of natural Bet v 1-specific IgG antibodies on IgE recognition of Bet v 1 and Bet v 1-induced basophil activation. METHODS: reactivity to folded recombinant Bet v 1, two unfolded recombinant Bet v 1 fragments comprising the N-terminal (F1) and C-terminal half of Bet v 1 (F2) and unfolded peptides spanning the corresponding sequences of Bet v 1 and the apple allergen Mal d 1 by ELISA or micro-array analysis. The ability of Bet v 1-specific serum antibodies from non-allergic subjects to inhibit allergic patients IgE or IgG binding to rBet v 1 or to unfolded Bet v 1-derivatives was assessed by competition ELISAs. Furthermore, the ability of serum antibodies from allergic and non-allergic subjects to modulate Bet v 1-induced basophil activation was investigated using rat basophilic leukaemia cells expressing the human FcεRI which had been loaded with IgE from BPA patients. RESULTS: antibodies from BPA, NBPA and NA subjects recognize mainly unfolded and sequential epitopes. IgG competition studies show that IgG specific for unfolded/sequential Bet v 1 epitopes is not inhibited by folded Bet v 1 and hence the latter seem to represent cryptic epitopes. IgG reactivity to Bet v 1 peptides did not correlate with IgG reactivity to the corresponding Mal d 1 peptides and therefore does not seem to be a result of primary sensitization to PR10 allergen-containing food. Natural Bet v 1-specific IgG antibodies inhibited IgE binding to Bet v 1 only poorly and could even enhance Bet v 1-specific basophil activation. CONCLUSION: IgE and IgG antibodies from BPA patients and birch pollen-exposed non-sensitized subjects recognize different epitopes. These findings explain why natural allergen-specific IgG do not protect against allergic symptoms and suggest that allergen-specific IgE and IgG have different clonal origin.