Okay, let's tackle this question. So, the patient is an 8-year-old boy with non-blanching rashes on the shins, knee joint swelling, hematuria, and proteinuria. The question is asking about the microscopic findings in a renal biopsy.

First, I need to recall the possible diagnoses. Non-blanching rashes, joint swelling, hematuria, and proteinuria are classic signs of a vasculitis, maybe Henoch-Schönlein purpura (HSP), which is IgA-mediated. HSP is common in children and often presents with these symptoms. The kidneys are involved in HSP, leading to IgA nephropathy. So the renal biopsy would show IgA deposits.

The core concept here is IgA nephropathy. The key is the IgA immune complexes depositing in the glomerular mesangium. Under microscopic examination, especially with immunofluorescence, you'd see granular IgA deposits. Light microscopy might show mesangial proliferation. If they mention electron microscopy, you'd see electron-dense deposits in the mesangium.

Now, the correct answer is likely IgA deposits. The other options would be different types of glomerulonephritis. For example, post-streptococcal GN is IgG and C3. Lupus nephritis might show IgG and IgM. Membranous nephropathy is IgG with subepithelial deposits. So each wrong option is associated with different immunoglobulins or patterns.

The clinical pearl here is to remember that HSP is associated with IgA nephropathy. The classic presentation is purpura, arthritis, abdominal pain, and renal involvement. The biopsy's immunofluorescence pattern is key for diagnosis.

So putting it all together, the correct answer is the one mentioning IgA deposits in the mesangium. The other options don't fit the clinical presentation and immunofluorescence findings.

**Core Concept**
The clinical scenario describes Henoch-Schönlein purpura (HSP), an IgA-mediated small-vessel vasculitis. Renal involvement in HSP leads to IgA nephropathy, characterized by mesangial IgA deposits in the glomeruli. This is a classic pediatric glomerulonephritis.

**Why the Correct Answer is Right**
In IgA nephropathy, immune complexes containing IgA1 accumulate in the glomerular mesangium. Immunofluorescence microscopy reveals granular IgA deposits in the mesangium, often with C3 complement. Light microscopy shows mesangial proliferation, and electron microscopy shows subendothelial and mesangial electron-dense deposits. This pattern directly correlates with the patient’s symptoms of purpura, arthritis, and hematuria.

**Why Each Wrong Option is Incorrect**
**Option A:** Post-streptococcal glomerulonephritis involves IgG and C3 deposits, not IgA.
**Option B:** Membranous nephropathy shows subepithelial IgG deposits, unrelated to HSP.
**Option C:** Lupus nephritis typically exhibits IgG and IgM deposits with a “full-house” pattern (C3, IgG, IgM).

**Clinical Pearl / High-Yield Fact**
Remember the **

✓ Correct Answer: C. Mesangial deposits of TgA