Complementation of Der p 2-induced histamine release from human basophils sensitized with monoclonal IgE: Not only by Ige, but also by IgG antibodies directed to a nonoverlapping epitope of Der p 2

The interaction of free allergen with two (or more) IgE molecules bound to the high-affinity receptor for IgE (FcεRI) on mast cells and basophilic granulocytes results in the release of inflammatory mediators. The role of allergen-specific IgG antibodies in the allergic reaction in human beings is less clear. We produced two chimeric IgE antibodies, hIgE-Dp2A and hIgE- Dp2B, directed to two nonoverlapping epitopes (A and B) of the house dust mite allergen Der p 2. Chimeric IgG1 and IgG4 variants of these antibodies were produced also. Basophil activation by the house dust mite allergen Der p 2 was induced after sensitization of basophils with a mixture of chimeric hIgE-Dp2A and hIgE-Dp2B antibodies but not after sensitization by the individual IgE antibodies alone. Basophil activation was also shown after sensitization with hIgE-Dp2A and stimulation with Der p 2 incubated with hIgG1-Dp2B or hIgG4-Dp2B antibodies. Both IgE and IgG antibodies directed to the other nonoverlapping epitope complemented the sensitization by the hIgE- Dp2A antibody. Nonsensitized basophils were not activated by the Der p 2/hIgG-Dp2 mixtures. These results indicate that allergen-specific IgG can complement an IgE-dependent reaction and therefore under certain conditions can act as an anaphylactic antibody.