Genetics and specific immune response in allergy to birch pollen and food:Evidence of a strong, positive association between atopy and the HLA classII allele HLA-DR7

Background: In some geographic areas birch pollen represents the most promi nent cause for airborne allergic diseases. Up to 70% of patients allergic t o birch pollen are hypersensitive to fruits, especially apples. Association s have been found, in some instances, with a sensitivity to aeroallergens a nd HLA class II genes. Objectives: We investigated whether susceptibility or resistance to birch p ollen allergy with and without food allergy was associated with HLA class I I genes. Methods: Blood samples were obtained from 2 groups of unrelated European-bo rn white adults: 42 atopic patients (31 of them with asthma) and 42 healthy control subjects with no personal or familial history of asthma or atopy. Their antibody responses to birch pollen, apples, grass, and weed pollens w ere evaluated by skin tests, RASTs, and immunoprints. Genomic DNA was extra cted from PBLs. The exons of DQA1, DQB1, DRB1, and DPB1 genes were selectiv ely amplified by using the PCR method. Genotyping was carried out by digest ion of the amplified DNA products with allele-specific endonucleases (PCR-R FLP), which recognize allelic variations in the polymorphic exon. Results: We found no significant differences in the frequency of DPB1 allel es between patients and control subjects. HLA class II DR4 and/or DR7 allel es were present in 42.6% of the patients and in only 2.4% of the healthy su bjects. These results confirm a previous study of a group of polysensitized atopic patients, which showed that DR4 and DR7 alleles were rare in health y control subjects and frequently observed in atopic subjects with or witho ut concomitant asthma. Conclusion: We conclude that the allele HLA-DR7 is significantly involved i n the presentation of apple and pollen allergens. However, we suggest that this susceptibility is more related to atop, than to specific responses to allergens.