Expression of a Human IgG4 Antibody, BAB2, with Specificity for the Major Birch Pollen Allergen, Bet v 1 in Escherichia coli: Recombinant BAB2 Fabs Enhance the Allergic Reaction

Abstract

Background: Antigen recognition by antibodies of different isotypes can result in completely different effects as exemplified by Type I allergy. While the IgE–antibody–mediated release of biological mediators constitutes the immunopathological basis for the immediate symptoms observed in allergic patients, allergen–specific IgG antibodies are thought to have protective effects. Methods: Cell lines secreting five human monoclonal IgG antibodies (BAB1–BAB5) with specificity for the major birch pollen allergen Bet v 1 were established from a birch–pollen–allergic patient who had received birch– pollen–specific immunotherapy. The influence of the Bet v 1–specific IgG antibodies on IgE binding to Bet v 1 was investigated. BAB2 was expressed in Escherichia coli as recombinant Fab, purified and tested for its ability to modulate Bet v 1–induced immediate–type skin reactions. Results: The BAB antibodies belonged to different IgG subclasses (BAB1: IgG1; BAB2, BAB3, BAB5: IgG4; and BAB4: IgG2) reflecting a tendency towards Th2. BAB1 represented the only antibody which strongly blocked IgE binding to Bet v 1, whereas BAB 3–BAB5 had little effect on IgE binding. Surprisingly, natural BAB2 antibodies as well as recombinant BAB2 Fabs strongly enhanced IgE binding to Bet v 1 and Bet v 1–induced immediate–type skin reactions and thus represent ‘enhancing antibodies’. Conclusion: The demonstration that anti–allergen IgG antibodies can also enhance IgE binding to a given allergen explains the unpredictability of specific immunotherapy as well as the controversy on the role of IgG in atopy.