Successful sublingual immunotherapy with birch pollen has limited effects on concomitant food allergy to apple and the immune response to the Bet v 1 homolog Mal d 1

Background

Cross-reactivity between the major birch pollen allergen, Bet v 1, and the apple protein, Mal d 1, frequently causes food allergy.

Objective

To investigate the effects of successful sublingual immunotherapy (SLIT) with birch pollen extract on apple allergy and the immune response to Bet v 1 and Mal d 1.

Methods

Before and after 1 year of SLIT, Bet v 1–sensitized patients with oral allergy syndrome to apple underwent nasal challenges with birch pollen and double-blind placebo-controlled food challenges with apple. Bet v 1–specific and Mal d 1–specific serum antibody levels and proliferation in PBMCs and allergen-specific T-cell lines (TCLs) were determined. Bet v 1–specific TCLs were mapped for T-cell epitopes.

Results

In 9 patients with improved nasal provocation scores to birch pollen, apple-induced oral allergy syndrome was not significantly reduced. Bet v 1–specific IgE and IgG₄ levels significantly increased. Bet v 1–specific T-cell responses to all epitopes and those cross-reactive with Mal d 1 significantly decreased. However, neither Mal d 1–specific IgE and IgG₄ levels nor Mal d 1–induced T-cell proliferation changed significantly. In contrast, Mal d 1–specific TCLs showed increased responses to Mal d 1 after 1 year of SLIT.

Conclusion

This longitudinal study indicates that pollen SLIT does not efficiently alter the immune response to pollen-related food allergens, which may explain why pollen-associated food allergy is frequently not ameliorated by pollen immunotherapy even if respiratory symptoms significantly improve.

Clinical implications

SLIT with birch pollen may have no clinical effect on associated apple allergy.

Key words: Birch pollen allergy, Bet v 1, food allergy, oral allergy syndrome, sublingual immunotherapy, cross-reactivity

Abbreviations used: aa, Amino acid, BU, Biological unit, DBPCFC, Double-blind, placebo-controlled food challenge, dpm, Δ cpm, NPT, Nasal provocation test, OAS, Oral allergy syndrome, SI, Stimulation index, SIT, Specific immunotherapy, SLIT, Sublingual immunotherapy, SPT, Skin prick test, TCL, T-cell line, VAS, Visual analog scale