# Impact of cross-linking stoichiometry on the structure and allergenicity of glutaraldehyde-polymerized allergen extracts

## TL;DR

This study shows how changing the amount of glutaraldehyde used to polymerize allergens affects their structure and how allergic they are, which is important for safer allergy treatments.

## Contribution

The study reveals how cross-linking stoichiometry influences polymer structure and allergenicity, enabling optimized allergen formulations for immunotherapy.

## Key findings

- Increased polymer size and density correlate with reduced allergenicity as measured by IgE reactivity and mast cell activation.
- High-density polymers retain native peptide profiles but show enhanced stability and lower allergenic potential.
- Optimized cross-linked polymers maintain immunogenicity comparable to native allergens in mouse models.

## Abstract

Polymerized allergen extracts are widely used in allergen immunotherapy (AIT) to reduce allergenicity and enhance safety. However, the impact of cross-linking stoichiometry on the structural and allergenic properties of these polymers remains insufficiently characterized. This study systematically investigates how varying glutaraldehyde-to-protein ratios influence the resulting polymers and their potential relevance for AIT.

Pollen extracts from Phleum pratense and Betula verrucosa were polymerized using five different glutaraldehyde-to-protein ratios. The resulting polymers were structurally characterized using SDS-PAGE, nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and mass spectrometry (MS). Allergenicity was evaluated by measuring the immunoglobulin E (IgE) reactivity through enzyme-linked immunosorbent assay (ELISA), Western blotting, and mast cell activation test (MAT). Immunogenicity was assessed by analyzing the serum-specific IgG and ex vivo lymphocyte responses in mice immunized with the least allergenic polymer formulation.

All cross-linking conditions produced polymers with distinct differences in size, morphology, and yield. Despite retaining similar peptide profiles to native allergens, as confirmed by MS, the polymers exhibited increased stability, as shown by NMR, and significantly reduced allergenicity, according to ELISA and MAT. Notably, increased polymer size and density, as determined by NMR and TEM, correlated with lower allergenicity. The most extensively cross-linked high-density polymers, optimized for minimal allergenicity, elicited immunogenic responses comparable to those induced by native extracts when tested against unmodified allergens.

Cross-linking stoichiometry critically shapes the structural and immunological properties of polymerized allergen extracts. Adjusting the glutaraldehyde-to-protein ratio to produce highly polymerized, dense polymers enables a well-balanced profile of safety and efficacy for use in AIT.

Diagram comparing native versus GA-polymerized allergen extracts, showing how polymerization with glutaraldehyde (GA) conceals epitopes and limits antibody binding. The right side illustrates how sub-optimal, optimal, and supra-optimal GA concentrations affect polymer structure, porosity, and IgE-mediated cell activation, with optimal GA reducing IgE binding and cell degranulation capacity.