Isotypic analysis of grass pollen-specific antibodies in human plasma. 4. Biological activity of allergen-specific and autoanti-IgE antibody fractions on basophil histamine release

Authors


Dr B. Basuyaux, Recherche et Développement, Luboratoire Français du Practionncment et des Biotechnologies, 3 avenue des lropiques BP305, F-91958 Les Ulis Cedex, France.

Summary

Background Blocking antibodies are defined as antibodies that compete with IgE for binding to allergens due to their specificity for those allergens. Thus, they may inhibit allergen-induced basophil and mast cell IgE-dependent mediator release both in vivo and in vitro.

Objective The present study was designed to evaluate the ability of antibodies isolated from human plasma samples on a Dactylis glomerata (Cocksfoot) pollen affinity-column to inhibit the Dactylis pollen-induced histamine release from human basophils (BHR) in vitro.

Methods Antibodies from Ig pools containing either high or low IgG4 anti-Dactylis pollen were purified on a Dactylis pollen affinity-column and then separated on an anti-human Igl column. Obtained Ig fractions were incubated for 30 min with Dactylis pollen allergens prior to incubation with basophils from Dactylis pollen-allergic donors. Cell supernatants were assessed for histamine content and the inhibition of BHR was calculated.

Results Unlike control non-isolated Igs, the antibodies isolated on the Dactylis pollen column were able to inhibit efficiently and in a dose-dependent manner Dactylis pollen-induced BHR. The inhibitory activity was increased in isolated antibody samples that had high Ig(i4 levels. Antibodies isolated on the Dactylis pollen column, however, consisted not only of true allergen-specific (potentially blocking) antibodies but also of autoanti-Igl- binding to allergen-specific IgE and mistaken for allergen-specific antibodies, thus opening to question the involvement of the true allergen-specific antibodies in the BHR-inhibitory activity. Unlike the true allergen-specific antibodies, the autoanti-Igl were retained on and eluted from the anti-lgF column. Results showed that both the autoanti-IgE-depleted and the autoanti-IgF-containing fractions accounted for the inhibition observed with the related non-depleted sample that had been isolated on the Dactylis pollen column.

Conclusion For the first time, the true blocking activity of allergen-specific antibodies is demonstrated, that is. in the absence of the autoanti-Igl which can also inhibit BHR.

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