Which type of hypersensitivity reaction is involved in the early phase of allergic rhinitis?

The early phase of allergic rhinitis is characterized by a Type I hypersensitivity reaction. This type of hypersensitivity, also known as an immediate hypersensitivity reaction, involves the activation of IgE antibodies that are produced in response to an allergen. When an individual with a sensitized immune system encounters the same allergen again, the allergen cross-links the IgE antibodies bound to mast cells and basophils, leading to their degranulation. This process releases various mediators such as histamine, leukotrienes, and prostaglandins, which cause the characteristic symptoms of allergic rhinitis, including sneezing, nasal congestion, and itching.

Understanding the mechanism of Type I hypersensitivity is crucial, as it underscores how allergens trigger an exaggerated immune response in susceptible individuals. This reaction can occur within minutes of exposure to the allergen, marking the early phase of its onset. In contrast, other types of hypersensitivity, such as Type II, Type III, and delayed-type hypersensitivity, involve different immune mechanisms and timelines, making them less relevant to the immediate symptoms experienced in allergic rhinitis.