Systemic lupus erythematosus is an example of which type of hypersensitivity reaction?
A.
Type IV
B.
Type III
C.
Type II
D.
Type I
The Correct Answer and Explanation is:
The correct answer is B. Type III.
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies against various cellular components, leading to widespread inflammation and tissue damage. This condition is an example of a Type III hypersensitivity reaction, also known as immune complex-mediated hypersensitivity.
Explanation:
Hypersensitivity Reactions Overview: Hypersensitivity reactions are classified into four types based on the underlying immune mechanism:
- Type I (Immediate Hypersensitivity): This reaction involves IgE antibodies and mast cells. It is commonly associated with allergies such as asthma, hay fever, and anaphylaxis. Upon initial exposure to an allergen, IgE antibodies are produced and bind to mast cells. Subsequent exposure to the allergen triggers the release of histamines and other mediators, causing symptoms like itching, swelling, and bronchoconstriction.
- Type II (Cytotoxic Hypersensitivity): This type involves IgG or IgM antibodies directed against antigens on the surface of cells or tissues. It leads to cell destruction through mechanisms like complement activation or antibody-dependent cellular cytotoxicity. Examples include hemolytic anemia and Goodpasture syndrome.
- Type III (Immune Complex-Mediated Hypersensitivity): In Type III reactions, immune complexes (antigen-antibody complexes) are formed and deposited in various tissues, including the skin, kidneys, and joints. These deposits trigger an inflammatory response through the activation of the complement system and recruitment of leukocytes. In SLE, autoantibodies form immune complexes with nuclear antigens. These immune complexes deposit in tissues, such as the skin, kidneys, and joints, leading to inflammation and damage.
- Type IV (Delayed-Type Hypersensitivity): This reaction involves T lymphocytes rather than antibodies. It is characterized by a delayed response, usually occurring 24-48 hours after exposure. Examples include contact dermatitis (e.g., poison ivy) and tuberculin skin tests.
Systemic Lupus Erythematosus and Type III Hypersensitivity: In SLE, the formation of autoantibody-antigen complexes, particularly against nuclear components such as DNA and histones, leads to the deposition of these complexes in tissues. The deposition causes local inflammation and damage due to the activation of complement and subsequent recruitment of inflammatory cells. This Type III hypersensitivity mechanism explains many of the clinical manifestations of SLE, including arthritis, skin rashes, and nephritis.
In summary, systemic lupus erythematosus is classified as a Type III hypersensitivity reaction because it primarily involves the formation and deposition of immune complexes, which lead to tissue inflammation and damage.