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

Background Blocking antibodies are defined as antibodies that compete with IgE for binding to allergens due to their specificity for those a llergens. Thus, they may inhibit allergen-induced basophil and mast ce ll 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 histami ne release from human basophils (BHR) in vitro. Methods Antibodies fro m Ig pools containing either high or low IgG4 anti-Dactylis pollen wer e purified on a Dactylis pollen affinity-column and then separated on an antihuman IgE column. Obtained Ig fractions were incubated for 30 m in with Dactylis pollen allergens prior to incubation with basophils f rom Dactylis pollen-allergic donors. Cell supernatants were assessed f or histamine content and the inhibition of BHR was calculated. Results Unlike control non-isolated Igs, the antibodies isolated on the Dacty lis pollen column were able to inhibit efficiently and in a dose-depen dent manner Dactylis pollen-induced BHR. The inhibitory activity was i ncreased in isolated antibody samples that had high IgG4 levels. Antib odies isolated on the Dactylis pollen column, however, consisted not o nly of true allergen-specific (potentially blocking) antibodies but al so of autoanti-IgE binding to allergen-specific IEE and mistaken for a llergen-specific antibodies, thus opening to question the involvement of the true allergen-specific antibodies in the BHR-inhibitory activit y. Unlike the true allergen-specific antibodies, the autoanti-IgE were retained on and eluted from the anti-IgE column. Results showed that both the autoanti-IgE-depleted and the autoanti-IgE-containing fractio ns accounted for the inhibition observed with the related non-depleted sample that had been isolated on the Dactylis pollen column. Conclusi on For the first time, the true blocking activity of allergen-specific antibodies is demonstrated, that is, in the absence of the autoanti-I gE which can also inhibit BHR.