Abstract
Oligomerization of allergens plays an important role in IgE-mediated reactions, as effective crosslinking of IgE- FcεRI complexes on the cell membrane is dependent on the number of exposed B-cell epitopes in a single allergen molecule or on the occurrence of identical epitopes in a symmetrical arrangement. Few studies have attempted to experimentally demonstrate the connection between allergen dimerization and the ability to trigger allergic reactions. Here we studied plant allergenic profilins rHev b 8 (rubber tree) and rZea m 12 (maize) because they represent an important example of cross-reactivity in the latex-pollen-food syndrome. Both allergens in their monomeric and dimeric states were isolated and characterized by exclusion chromatography and mass spectrometry and were used in immunological in vitro experiments. Their crystal structures were solved, and for Hev b 8 a disulfide-linked homodimer was found. Comparing the structures we established that the longest loop is relevant for recognition by IgE antibodies, whereas the conserved regions are important for cross-reactivity. We produced a novel monoclonal murine IgE (mAb 2F5), specific for rHev b 8, which was useful to provide evidence that profilin dimerization considerably increases the IgE-mediated degranulation in rat basophilic leukemia cells.
Highlights
It has been recognized that the study of protein oligomerization is relevant from several perspectives, since this phenomenon can regulate the function of the protein or can create higher-order structures[1]
Studies concerning the oligomerization of this plant allergen are scarce; it has been shown that two profilin isoforms (Art v 4.01 and Art v 4.02) from mugwort pollen form dimers and tetramers that are stabilized by disulfide bonds or ionic interactions, and it was postulated that the oligomerization of these molecules increased their allergenicity[16]
The same authors found, in western blot experiments, that oligomers of these profilin isoforms did not differ in their ability to bind serum IgE from allergic patients; when compared with the results obtained with the monomers; they proposed that oligomers would have additional epitopes, which would increase their allergenic potential
Summary
It has been recognized that the study of protein oligomerization is relevant from several perspectives, since this phenomenon can regulate the function of the protein or can create higher-order structures[1]. An important implication of protein oligomerization has been acknowledged in type I hypersensitivity reactions, where the effect of allergen dimerization and their multivalent characteristics promotes its recognition by specific IgE antibodies bound to high affinity FcεRI receptors on the surface of mast cells and basophils[2]. This interaction triggers the cross-linking of FcεRI on the effector cell membranes, and a concomitant activation of biochemical pathways leads to degranulation and the release of various mediators such as histamine and lipids, which cause inflammatory reactions[3]. We demonstrated that the dimeric form of rHev b 8 is more efficient than the monomeric form promoting significant degranulation in rat basophilic leukemia cells (RBL-2H3)
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