D2.394 - A class-variable immunoglobulin response to birch (B. pendula) pollen allergens

A classical IgE-mediated reaction is the primary immune response to birch allergens in sensitized individuals, manifesting as symptoms of allergic rhinitis, conjunctivitis, and asthma. However, it has been suggested that IgG antibodies may recognize different epitopes on birch allergens, indicating the possibility of non-IgE-mediated allergic responses. The aim of this study was to compare sensitized and non-sensitized individuals, distinguishing between IgE- and IgG-mediated response to selected birch pollen proteins.

Birch pollen material was collected from nine selected sites in Kraków and its vicinity, within a radius of up to 80 km. The study group consisted of 30 individuals with a confirmed allergy to birch pollen (22 females; mean age: 44.2 years, ±14.4), while the control group included 30 individuals without birch allergy (25 females; mean age: 41.8 years, ±11.6). Specific serum immunoglobulins (sIgE and sIgG, including sIgG4) against birch extracts were quantified using ImmunoCAP. Immunoblotting was performed on all participants sera using SDS-PAGE-separated field samples from 11 different birch pollen collections, with bound immunoglobulins detected using anti-human IgG and IgE secondary antibodies.

The concentration of sIgE against birch pollen extracts in sensitized patients ranged from 1.72 IU/l to 72.69 IU/l. In the study group, sIgG and sIgG4 levels were also significantly elevated (p<0.001 in both cases) compared to controls and ranged from 1.93 to 10.29 mgA/L and from 0.02 to 3.69 mgA/L (respectively). However, sIgG4 levels showed greater variability among patients than among controls. Our study demonstrated that highly sensitized individuals (with higher sIgE levels) had a higher sIgG4/sIgG ratio. Immunoblot analysis revealed strong sIgG binding in patients, with a correlation between the number of immunoreactive pollen protein bands and sIgE concentration (R²=0.41). In both sensitized and non-sensitized individuals, the most commonly detected protein band of 32 kDa has been identified, with little variation among the tested samples. In the study group, Bet v1 was the predominant allergen recognized by anti-human IgE antibodies. A strong differentiations among birch specimen in terms of immunoblotting spectra were also observed. 

Our study provides novel insights into the natural allergen-specific IgG response in allergic and non-allergic individuals. These findings may have important implications for allergen-specific immunotherapy, particularly in the context of passive immunization or protective effects.

AcknowledgementsThe study was supported by the grant of the National Science Centre, 2021/41/B/NZ8/00981