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Structure of a patient-derived antibody in complex with allergen reveals simultaneous conventional and superantigen-like recognition

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)E8707-E8716
JournalProceedings of the National Academy of Sciences of the United States of America
Volume115
Issue number37
Early online date27 Aug 2018
DOIs
Publication statusPublished - 11 Sep 2018

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Abstract

Antibodies classically bind antigens via their complementarity-determining regions, but an alternative mode of interaction involving V-domain framework regions has been observed for some B-cell “superantigens”. We report the first crystal structure of an antibody employing both modes of interaction simultaneously and binding two antigen molecules. This human antibody from an allergic individual binds to the grass pollen allergen Phl p 7. Not only are two allergen molecules bound to each antibody Fab, but also each allergen molecule is bound by two Fabs: one epitope is recognized classically, the other in a superantigen-like manner. A single allergen molecule thus cross-links two identical Fabs, contrary to the one-antibody/one-epitope dogma which dictates that a dimeric allergen at least is required for this to occur. Allergens trigger immediate hypersensitivity reactions by cross-linking receptor-bound IgE molecules on effector cells. We found that monomeric Phl p 7 induced degranulation of basophils sensitized solely with this monoclonal antibody expressed as an IgE, demonstrating that the dual specificity has functional consequences. The monomeric state of Phl p 7 and two structurally-related allergens was confirmed by size-exclusion chromatography and multi-angle laser light scattering, and the results were supported by degranulation studies with the related allergens, a second patient-derived allergen-specific antibody lacking the non-classical binding site, and mutagenesis of the non-classically recognized allergen epitope. This antibody dual reactivity and novel cross-linking mechanism not only has implications for understanding allergenicity and allergen potency, but importantly has broader relevance to antigen recognition by membrane immunoglobulin and cross-linking of the B-cell receptor.

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