The blocking activity of birch pollen-specific immunotherapy-induced IgG4 is not qualitatively superior to that of other IgG subclasses

Allergen-specific IgG antibodies induced by specific immunotherapy (SIT) interfere with the allergen-IoE interaction, and act as blocking antibodies in vitro. It has been hypothesised that IgG4, as opposed to other IgG subclasses, is particularly important in this function, which may play a role for the clinical efficacy of SIT. In this study, fractionated serum samples from 14 SIT-treated birch pollen allergic individuals enabled determination of the inhibitory capacity of IgG4 alone versus non-IgG4 IgG. Allergen-binding activities of IaG and the IgG-mediated inhibition of allergen binding to I-labelled rBet v 1.2801, a recombinant variant of the major allergen of Betula verrucosa pollen. autologus IgE were detected using 125 Results show that IgG4-depletion resulted in equivalent reductions in binding and blocking activities. In contrast, a significant but less than two-fold higher relative blocking activity was found in the purified IgG4 fraction. There was no significant difference in the binding avidities (1/K-d) measured in the two IgG fractions. Thus, it appears that SIT-induced specific IgG4 contributes to the I-G blocking of allergen binding to IgE in a simple quantitative manner and not by a particular intrinsic blocking activity. (C) 2004 Elsevier Ltd. All rights reserved.