Hypersensitivity and IgE-mediated allergy. (A) Upon initial exposure to an allergen, there will be no overt manifestations of allergic disease because the patient is nonsensitized. However, this allergen will initiate an immune response that results in the synthesis of IgE and sensitization of the susceptible (atopic) host. (B) Upon subsequent, repeated exposures, this sensitized individual will synthesize increased amounts of IgE, thus becoming hypersensitive, although mild allergic symptoms may or may not be present. (C) From this point onward, reexposure to this specific allergen will provoke the overt manifestations of allergic disease. Source: Fireman and Slavin, 1991.