Final answer:
Hypersensitivities are exaggerated immune responses to allergens, with Type I hypersensitivity being an immediate reaction involving IgE antibodies and mast cell degranulation, causing symptoms such as hives or anaphylactic shock. Other types include Type II hypersensitivity and delayed reactions like contact sensitivity, but the most common allergic reactions are immediate and IgE mediated.
Step-by-step explanation:
Immune-mediated allergies, or hypersensitivities, are exaggerated immune responses to substances that are usually harmless to most people, known as allergens. These responses can be classified into different types, with the most common being Type I hypersensitivity. This immediate reaction involves sensitization of mast cells with an antibody called IgE. Sensitization occurs upon an individual's first exposure to an allergen, leading to an IgE antibody response.With subsequent exposure to the same allergen, these IgE antibodies cause mast cells to degranulate, releasing chemical mediators such as histamine and serotonin that trigger allergic reactions. Symptoms can range from mild, like sneezing and itchy eyes, to severe, such as anaphylactic shock, a life-threatening condition. A notable example of a Type I hypersensitivity is an allergic skin disease, where contact with an allergen like pollen or animal dander causes skin irritation or hives.Other forms of hypersensitivity include Type II, where antibodies attack antigens on cell surfaces, potentially leading to conditions like hemolytic transfusion reactions. Whereas delayed hypersensitivity reactions, such as contact sensitivity from materials like nickel, don't immediately trigger symptoms. These reactions are mediated by T cells and can result in red, swollen areas on the skin.