Final answer:
Hay fever and asthma are caused by the IgE isotype on the first encounter with an allergen, producing a quick reaction classified as immediate hypersensitivity, where IgE-mediated mast cell degranulation releases histamines and other substances that cause allergy symptoms.
Step-by-step explanation:
Hay fever and asthma are allergic reactions triggered by the immune system's response to allergens. On the first encounter with an allergen, the body produces antibodies of the IgE isotype. This immunoglobulin class specializes in mediating allergic reactions, including asthma and hay fever. IgE antibodies bind to mast cells, which upon subsequent exposure to the same allergen, release histamines and other substances that cause the symptoms of allergies. Thus, the correct answer to the question is c) IgE.
Furthermore, a pollen allergy is classified as d) immediate hypersensitivity. This type of hypersensitivity reaction occurs quickly, often within minutes of exposure to the allergen, and is IgE-mediated. Immediate hypersensitivity reactions involve mast cell degranulation caused by the cross-linking of surface IgE by antigen, leading to symptoms such as sneezing, itching, and difficulty breathing in the case of asthma.