Which type of hypersensitivity is known for immune complex formation?

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Answer: (C)

Type III hypersensitivity is characterized by the formation of immune complexes. This occurs when antibodies bind to soluble antigens, leading to the formation of complexes that can deposit in various tissues. These immune complexes can trigger an inflammatory response, as they activate the complement system and attract inflammatory cells, particularly neutrophils, to the site of deposition. This process is particularly relevant in conditions such as systemic lupus erythematosus and rheumatoid arthritis, where immune complexes play a crucial role in the pathogenesis of tissue damage and inflammation.

In contrast, Type I hypersensitivity is associated with immediate allergic reactions due to IgE antibodies and mast cell degranulation. Type II hypersensitivity involves antibody-mediated destruction of cells or tissues, often through mechanisms like opsonization or complement-mediated lysis, but does not primarily involve immune complex formation. Type IV hypersensitivity, also known as delayed-type hypersensitivity, is mediated by T cells and does not involve antibodies or immune complexes. Each type of hypersensitivity has distinct mechanisms and clinical manifestations, making Type III uniquely identified by immune complex formation.