Background
The extensive similarities between helminth proteins and allergens are thought to contribute to helminth-driven allergic sensitization.
Objective
To investigate the cross-reactivity between a major glutathione-S transferase (GST) allergen of cockroach (Bla g 5) and the GST of Wuchereria bancrofti (WbGST), a major lymphatic filarial pathogen of humans.
Methods
We compared the molecular and structural similarities between Bla g 5 and WbGST by in silico analysis and by linear epitope mapping. Levels of IgE, IgG and IgG4 antibodies were measured in filarial-infected and –uninfected patients. Mice were infected with Heligmosomoides bakeri (Hb) and skin tested for cross-reactive allergic responses.
Results
These two proteins are 30% identical at the amino acid level with remarkable similarity in the N-terminal region and overall structural conservation based on predicted three-dimensional models. Filarial infection was associated with IgE, IgG, and IgG4 anti-Bla g 5 Ab production, with a significant correlation between Abs (irrespective of isotype) to Bla g 5 and WbGST (P < 0.0003). Pre-incubation of sera from cockroach allergic subjects with WbGST partially depleted (by 50 to 70%) anti-Bla g 5 IgE, IgG, and IgG4 Abs. IgE epitope mapping of Bla g 5 revealed that two linear N-terminal epitopes are highly conserved in WbGST corresponding to Bla g 5 peptides partially involved in the inhibition of WbGST binding. Finally, mice infected with Hb developed anti-HbGST IgE and showed immediate type skin test reactivity to Bla g 5.
Conclusion
These data demonstrate that helminth GST and the aeroallergen Bla g 5 share epitopes that can induce allergic cross-sensitization.
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