Serum IgG₄ responses to allergen immunotherapy are well documented as blocking allergen binding to receptor-bound IgE on antigen-presenting cells and effector cells, but the molecular characteristics of treatment-induced IgG₄, particularly in relation to expressed antibody, are poorly defined.

We aimed to clone and express recombinant IgG₄ from patients receiving grass pollen immunotherapy using single B cells to obtain matched heavy- and light-chain pairs.

IgG₄⁺ B cells were enriched from blood samples taken from 5 patients receiving grass pollen immunotherapy. Matched heavy- and light-chain variable-region sequences were amplified from single IgG₄⁺ B cells. Variable regions were cloned and expressed as recombinant IgG₄. Binding analysis of grass pollen–specific IgG₄ was performed by using surface plasmon resonance. Functional assays were used to determine IgE blocking activity. In a separate experiment grass pollen–specific antibodies were depleted from serum samples to determine the proportion of grass pollen–specific IgG₄ within total IgG₄.

Depletion of grass pollen–specific antibodies from serum led to a modest reduction in total IgG₄ levels. Matched heavy- and light-chain sequences were cloned from single IgG₄⁺ B cells and expressed as recombinant IgG₄. We identified an IgG₄ that binds with extremely high affinity to the grass pollen allergen Phl p 7. Furthermore, we found that a single specific mAb can block IgE-mediated facilitated allergen presentation, as well as IgE-mediated basophil activation.

Although increases in IgG₄ levels cannot be wholly accounted for within the allergen-specific fraction, allergen immunotherapy might result in the production of high-affinity allergen-specific blocking IgG₄.