Methods: The sera of 69 patients sensitized to P. pratense were tested. All these patients had signs and symptoms of rhinoconjunctivitis with, or without, asthma in May and June of 2011. All these patients had positive skin prick tests to a standardized extract of P. pratense, and other grass species. Most patients were also sensitized to olive pollen. Specific IgE and IgG binding were analysed by direct ELISA against P. pratense native (non modified) and allergoid extracts. Relative potencies was evaluated through ELISA inhibition assays, and the protein composition of non-modified and allergoid samples was determined by Mass Spectrometry (MS/MS).
Results: Mean Specific IgE levels against the native extract was 16.68 ± 11.65 Units (U) and against the allergoid: 7.26 ± 8.24 U (p < 0.0001; Mann-Whitney). On the other hand, mean specific IgG binding against the non-modified extract was 90.34 ±75.57 U versus 76.19 ± 70.31 U against the allergoid (p = 0.16; Mann-Whitney). Linear regression coefficients obtained between immunoglobulin reactivity against both extracts were: r2 = 0.51 for specific IgE and r2 = 0.83 for specific IgG. An important decrease in the allergenic activity, measured by inhibition ELISA, was clearly observed. The MS/MS assay revealed the presence of the mayor allergen, and some isoforms, in non-modified and allergoid extracts.
Conclusions: Results obtained demonstrate that the glutaraldehyde polymerization process induces an important decrease in specific IgE binding to allergoids of P. pratense while there are no significant differences in specific IgG binding. The allergenic composition of the P. pratense allergoid was equivalent to the non-modified pollen extract.