**Core Concept**
The patient's symptoms, including arthritis, skin rash, abdominal colic, and hematuria (red blood cells in urine), suggest a systemic vasculitic process. This is likely triggered by an abnormal immune response following an upper respiratory tract infection. The glomerular deposition of immunoglobulins is a hallmark of immune complex-mediated glomerulonephritis.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with Henoch-Schönlein purpura (HSP), a form of systemic vasculitis that affects small blood vessels. HSP is characterized by the deposition of IgA immune complexes in the affected tissues, including the kidneys. The glomerular deposition of IgA immune complexes is a key feature of HSP nephritis, which can lead to hematuria, proteinuria, and renal failure if left untreated. The bright red urine and presence of red blood cells on microscopic examination suggest that the kidney is involved.

**Why Each Wrong Option is Incorrect**
**Option A:** IgG is the most abundant immunoglobulin in the serum and is involved in various immune responses, but it is not the primary immunoglobulin deposited in HSP nephritis.
**Option B:** IgM is an immunoglobulin that plays a key role in the early immune response, but it is not typically associated with HSP nephritis.
**Option C:** IgE is an immunoglobulin involved in allergic reactions, but it is not relevant to HSP nephritis.

**Clinical Pearl / High-Yield Fact**
HSP nephritis can present with a range of symptoms, including hematuria, proteinuria, and renal failure. It is essential to consider HSP in the differential diagnosis of patients with systemic vasculitis and kidney involvement.

**Correct Answer:** C. IgA.