**Core Concept**
Post-streptococcal glomerulonephritis (PSGN) is an immune complex-mediated glomerulonephritis that occurs after an infection with certain strains of Group A beta-hemolytic Streptococcus (GABHS). It is characterized by the deposition of immune complexes containing streptococcal antigens and host antibodies in the glomeruli, leading to inflammation and damage.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of PSGN. Immune complexes form when antibodies bind to the streptococcal antigens, and these complexes are then deposited in the glomeruli, triggering an inflammatory response. This is mediated by the complement system, particularly the activation of C3 and the formation of C5b-9 membrane attack complex (MAC). The deposition of immune complexes and activation of the complement system lead to the activation of glomerular cells, including mesangial cells and endothelial cells, resulting in the characteristic histological findings of PSGN.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the pathophysiology of PSGN.
**Option B:** This option is incorrect because PSGN is not primarily caused by a deficiency in the complement system.
**Option C:** This option is incorrect because PSGN is not primarily caused by a genetic predisposition.

**Clinical Pearl / High-Yield Fact**
PSGN typically presents 1-3 weeks after an infection with GABHS, and the risk of developing PSGN is highest in children and young adults.

**Correct Answer: C. Immune complex deposition.