Hypersensitivity

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Hypersensitivity refers to abnormal reactions of the immune system that occur in response to exposure to certain substances, called antigens.

Hypersensitivity pneumonitis Case 127 (4698396942)

Overview

Hypersensitivity reactions can occur when the immune system responds too aggressively or inappropriately to a harmless or otherwise normal antigen. This reaction can result in inflammation and damage to the body's own tissues.

Types of Hypersensitivity

There are four primary types of hypersensitivity reactions, classified as Type I, II, III, and IV.

• Type I hypersensitivity: Also known as immediate or anaphylactic hypersensitivity, this type includes common allergies to pollen, food, insect stings, and some medications. Symptoms can range from mild (sneezing, itching) to severe (anaphylaxis, a potentially fatal systemic reaction).
• Type II hypersensitivity: This type, or cytotoxic hypersensitivity, involves the immune system attacking the body's own cells, leading to conditions like hemolytic anemia or thrombocytopenia.
• Type III hypersensitivity: Also known as immune complex hypersensitivity, this reaction occurs when immune complexes are not adequately cleared, leading to inflammation and tissue damage. It's often associated with autoimmune conditions such as systemic lupus erythematosus.
• Type IV hypersensitivity: This type, or delayed-type hypersensitivity, is mediated by T cells and typically takes 48-72 hours to develop. Examples include contact dermatitis (like poison ivy rash) and the tuberculin skin test.

Diagnosis

Diagnosis of hypersensitivity involves identifying the specific antigen causing the reaction. This may involve skin tests, blood tests, and in some cases, challenge tests where small amounts of the suspected antigen are introduced under controlled conditions.

Treatment and Management

Treatment depends on the type of hypersensitivity and may include:

Avoiding the allergen Medications to control symptoms, such as antihistamines, corticosteroids, or epinephrine Immunotherapy (allergy shots) to gradually desensitize the immune system to the allergen

See Also

• Allergy
• Autoimmunity
• Anaphylaxis
• Immunology

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