**Core Concept**
Poststreptococcal glomerulonephritis (PSGN) is a type of acute nephritic syndrome characterized by rapid onset of hematuria, proteinuria, and renal failure following a streptococcal infection. The prognosis for PSGN is generally better than for other forms of rapidly progressive glomerulonephritis due to the immune-mediated pathogenesis and the body's ability to clear the antigen.

**Why the Correct Answer is Right**
PSGN is associated with the formation of immune complexes and the activation of the complement system, leading to inflammation and damage to the glomerular capillaries. The immune response is primarily directed against the nephritogenic strains of group A beta-hemolytic streptococci, which triggers a cascade of events resulting in the characteristic nephritic syndrome. In contrast to other forms of rapidly progressive glomerulonephritis, PSGN tends to have a more favorable prognosis due to the body's ability to clear the antigen and the relatively limited extent of glomerular damage.

**Why Each Wrong Option is Incorrect**
**Option B:** Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that can cause glomerulonephritis, but the prognosis is generally worse than in PSGN due to the complex and multifactorial pathogenesis of SLE.
**Option C:** Henoch-Schoenlein purpura is a form of vasculitis that can affect the kidneys, but it tends to have a more variable and often poorer prognosis than PSGN due to the involvement of small blood vessels and the potential for renal scarring.
**Option D:** Polyarteritis nodosa is a form of medium vessel vasculitis that can affect the kidneys, but it tends to have a worse prognosis than PSGN due to the involvement of larger blood vessels and the potential for renal infarction.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that PSGN tends to have a better prognosis than other forms of rapidly progressive glomerulonephritis, but this does not mean that patients with PSGN do not require close monitoring and potentially aggressive treatment. A high index of suspicion for PSGN should be maintained in patients presenting with acute nephritic syndrome following a streptococcal infection.

**✓ Correct Answer: A. Poststreptococcal glomerulonephritis**