Sialic acid-binding immunoglobulin-like lectin-8 (Siglec-8) promotes the apoptosis of eosinophils and inhibits FceRI-dependent mediator release from mast cells. We investigated the genetic association between sequence variants in Siglec-8 and diagnosis of asthma, total levels of serum IgE (tIgE), and diagnosis of eosinophilic esophagitis (EE) in diverse populations. The effect of sequence variants on Siglec-8 glycan ligand-binding activity was also examined. Significant association with asthma was observed for SNP rs36498 (odds ratios (OR), 0.69, P¼8.8Â10 À5 ) among African Americans and for SNP rs10409962 (Ser/Pro) in the Japanese population (OR, 0.69, P¼0.019). Supporting this finding, we observed association between SNP rs36498 and current asthma among Brazilian families (P¼0.013). Significant association with tIgE was observed for SNP rs6509541 among African Americans (P¼0.016), and replicated among the Brazilian families (P¼0.02). In contrast, no association was observed with EE in Caucasians. By using a synthetic polymer decorated with 6¢-sulfo-sLe x , a known Siglec-8 glycan ligand, we did not find any differences between the ligand-binding activity of HEK293 cells stably transfected with the rs10409962 risk allele or the WT allele. However, our association results suggest that the Siglec8 gene may be a susceptibility locus for asthma.
Background: Bermuda grass pollen (BGP) is an important seasonal aeroallergen worldwide which induces allergic disorders such as allergic rhinitis, conjunctivitis and asthma. Cyn d 1 is the major allergen of BGP. This study is aimed to map human IgE and IgG4 antibody-binding sequential epitopes on Cyn d 1 by dot immunoblotting. Methods: Synthetic peptides (10-mers; 5 overlapping residues) spanning the full length of Cyn d 1 were used for dot immunoblotting to map human IgE and IgG1–4 antibody-binding regions with sera from BGP-allergic patients. Synthetic peptides with more overlapping residues were used for further mapping. Essential amino acids in each epitope were examined by single amino acid substitution with alanine. Peptides with sequence polymorphism of epitopes of Cyn d 1 were also synthesized to extrapolate their differences in binding capability. Results: Four major IgE-binding epitopes (peptides 15–1, 21, 33–2 and 35+1, corresponding to amino acids 70–79, 101–110, 159–167 and 172–181) and 5 major IgG4-binding epitopes (peptides 15–1, 30–2, 33–2, 35+1 and 39, corresponding to amino acids 70–79, 144–153, 159–167, 172–181 and 192–200) were identified. They are all located on the surface of the simulated Cyn d 1 molecule, and three of them are major epitopes for both IgE and IgG4. Their critical amino acids were all characterized. Major epitopes for human IgG1 to IgG4 are almost identical. Conclusions: This is the first study to map the sequential epitopes for human IgE and IgG4 subclasses in Cyn d 1. It will be helpful for future development in immunotherapy and diagnosis.
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