Type I hypersensitivity

Overview of Type I hypersensitivity

Diagram illustrating the mechanism of Type I hypersensitivity.

Detailed pathway of Type I hypersensitivity reactions.

Type I hypersensitivity, also known as immediate hypersensitivity, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. This reaction is mediated by immunoglobulin E (IgE) antibodies and is characterized by rapid onset, typically occurring within minutes of exposure to the allergen.

Mechanism

Type I hypersensitivity involves a two-phase process:

Sensitization

During the initial exposure to an allergen, the immune system responds by producing IgE antibodies specific to that allergen. These IgE antibodies bind to FcεRI receptors on the surface of mast cells and basophils. This process is known as sensitization.

Re-exposure

Upon subsequent exposure to the same allergen, the allergen cross-links the IgE antibodies on the surface of mast cells and basophils, triggering these cells to degranulate. This degranulation releases various mediators, including histamine, leukotrienes, and prostaglandins, which lead to the symptoms of an allergic reaction.

Symptoms

The symptoms of Type I hypersensitivity can vary depending on the route of exposure and the individual. Common symptoms include:

• Urticaria (hives)
• Rhinitis (runny nose)
• Asthma
• Anaphylaxis, a severe, life-threatening reaction

Examples

Common examples of Type I hypersensitivity reactions include:

• Allergic rhinitis (hay fever)
• Allergic asthma
• Food allergies
• Insect sting allergies

Diagnosis

Diagnosis of Type I hypersensitivity typically involves:

• Skin prick test
• Serum IgE testing
• Challenge testing

Treatment

Treatment options for Type I hypersensitivity include:

• Avoidance of known allergens
• Antihistamines
• Corticosteroids
• Epinephrine for anaphylaxis
• Allergen immunotherapy

Also see

• Type II hypersensitivity
• Type III hypersensitivity
• Type IV hypersensitivity
• Allergy
• Immune system