Final answer:
IgE is the class of antibody that binds to mast cells and triggers allergic reactions upon exposure to allergens.
Step-by-step explanation:
The class of human antibody that attaches to mast cells and plays a major role in allergic reactions is IgE. This antibody is synthesized by plasma cells in response to an allergen and binds to mast cells. Upon secondary exposure to the allergen, these mast cells release histamines and other inflammatory mediators, leading to the symptoms of an allergic reaction, such as sneezing, itchy eyes, and in severe cases, anaphylaxis.
The interaction between IgE antibodies and mast cells is a defense mechanism against parasites, but it is also the basis for allergic responses when it is mistakenly triggered by harmless substances.