What characterizes an individual who has undergone sensitization?

An individual who has undergone sensitization typically shows a significant immunological response to an allergen, meaning their body has developed a heightened sensitivity to that substance. This process includes the formation of specific antibodies, primarily immunoglobulin E (IgE), which bind to mast cells. When re-exposed to the same allergen, these mast cells release chemical mediators such as histamine, leading to allergic reactions. The correct identification of this characteristic is crucial in understanding allergic responses and managing conditions like asthma, allergic rhinitis, and anaphylaxis.

The other options do not accurately reflect what occurs during sensitization. For instance, the notion that an individual no longer reacts to allergens contradicts the very definition of sensitization, which implies an increased reactivity. Similarly, producing antigens to combat allergens is not how the immune response works; rather, it is the development of antibodies that is crucial. Furthermore, while constant exposure to allergens can exacerbate reactions, it is not a defining characteristic of sensitization itself.