During sensitization with hapten-carrier adducts, a gradual increase of drug-specific IgE occurs, which binds to FcεRI on MC. The MC-bound specific IgE binds the hapten-carrier adducts. The slow increase of IgE and IgE-antigen complexes leads to a gradual desensitization of mast cells, which is specific for this antigen/allergen. In initial sensitization, the limiting factor is IgE;