Final answer:
The first exposure to an antigen is called sensitization. IgE antibodies are present on mast cells and basophils. During the second exposure, the allergen causes the release of histamines and other inflammatory mediators.
Step-by-step explanation:
The first exposure to an antigen is called sensitization. As a result, IgE antibodies are present on mast cells and basophils. During the second exposure, the allergen causes the release of histamines and other inflammatory mediators.