Acute poststreptococcal glomerulonephritis is characterised by which of the following hypersensitivity reactions?
**Core Concept**
Acute poststreptococcal glomerulonephritis (APSGN) is a renal disease that occurs as a complication of streptococcal infection, typically following pharyngitis or skin infections caused by group A beta-hemolytic streptococci (GABHS). The pathogenesis of APSGN involves the formation of immune complexes, which play a crucial role in the disease's development.
**Why the Correct Answer is Right**
APSGN is characterized by the formation of immune complexes consisting of antibodies against streptococcal antigens and the antigens themselves. These immune complexes deposit in the glomeruli, leading to activation of the complement system and subsequent inflammation. The type III hypersensitivity reaction, also known as immune complex hypersensitivity, occurs when these immune complexes deposit in tissues, such as the glomeruli, and trigger an inflammatory response. This reaction is mediated by the activation of complement components, particularly C3, and the recruitment of neutrophils and macrophages to the affected area.
**Why Each Wrong Option is Incorrect**
**Option A:** Type II hypersensitivity involves the formation of antibodies against cell surface antigens, leading to cell destruction through mechanisms such as complement activation or antibody-dependent cellular cytotoxicity. This is not the primary mechanism underlying APSGN.
**Option B:** Type IV hypersensitivity is a cell-mediated reaction, which involves T lymphocytes and the release of cytokines, rather than the formation of immune complexes. This reaction is seen in conditions such as contact dermatitis and tuberculosis.
**Option C:** Tuberculin-Type Hypersensitivity is a type of delayed hypersensitivity reaction, which is mediated by T lymphocytes and is seen in response to the tuberculin skin test. This reaction is not directly related to the pathogenesis of APSGN.
**Clinical Pearl / High-Yield Fact**
APSGN typically occurs 1-3 weeks after the initial streptococcal infection and is characterized by hematuria, proteinuria, and hypertension. The disease is often self-limiting, but complications such as chronic kidney disease and end-stage renal disease can occur in some cases.
**✓ Correct Answer:** D. Type III: Immune Complex Hypersensitivity