**Question:** Crescent formation is characteristic of the following glomerular disease:

A. Lupus nephritis
B. Membranous glomerulonephritis
C. IgA nephropathy
D. Minimal change disease

**Core Concept:**
Crescent formation refers to the formation of a fibrocellular or fibrous capsule around a glomerulus, resulting in the loss of glomerular filtration function. This is a hallmark feature of certain glomerular diseases, which are categorized into primary and secondary causes. Glomerular diseases can be broadly classified into five classes based on the type of immune complex deposition: mesangial, subendothelial, subepithelial, intramembranous, and extracapillary.

**Why the Correct Answer is Right:**
Crescent formation is characteristic of the extracapillary type of glomerulonephritis. In this type, immune complex deposition occurs in the outer layer of the glomerular capillary wall, leading to destruction of the capillary loop and the formation of a crescent. This is seen in the following diseases:

1. **A. Lupus nephritis (Class IV):** In this type, immune complex deposition occurs in the subepithelial region of the glomerular capillary wall, leading to the formation of a crescent. Lupus nephritis is a manifestation of systemic lupus erythematosus and is characterized by the presence of immune complex deposition and inflammation in the glomerulus.
2. **B. Membranoproliferative glomerulonephritis (Class V):** In this type, immune complex deposition occurs in the subendothelial region of the glomerular capillary wall, leading to the formation of a crescent. Membranoproliferative glomerulonephritis is a rare condition characterized by immune complex deposition, mesangial proliferation, and crescent formation.
3. **C. IgA nephropathy (Bosley-Salih disease):** In this type, immune complex deposition occurs in the mesangium, leading to mesangial cell proliferation and crescent formation. IgA nephropathy is characterized by immune complex deposition in the mesangium and subsequent inflammation and fibrosis leading to renal dysfunction.
4. **D. Minimal change disease:** Minimal change disease is a type of nephrotic syndrome characterized by focal and segmental podocyte foot process effacement, without immune complex deposition or inflammation. It is not associated with crescent formation.

**Why Each Wrong Answer is Incorrect:**
A. **A. Lupus nephritis (Class IV):** Although lupus nephritis is associated with immune complex deposition and inflammation, it is not characterized by crescent formation. Crescent formation is a feature of membranoproliferative glomerulonephritis (Bosley-Salih disease) and membranous nephropathy.
B. **B. Membranous nephropathy:** Membranous nephropathy is characterized by immune complex deposition beneath the subendothelial basement membrane, leading to a thickening of the glomerular basement membrane and crescent formation. Membran