A 25-year-old man comes to the emergency department due to sudden-onset fatigue and dark urine.  The patient was recently diagnosed with dermatitis herpetiformis.  He began treatment with dapsone and a gluten-free diet 3 days ago.  This morning, the patient felt weak and had difficulty getting out of bed.  His urine also appeared dark.  Temperature is 37 C, blood pressure is 129/75 mm Hg, pulse is 87/min, and respirations are 15/min.  The patient appears tired.  Examination shows scleral icterus and pale lips.  There is a papular rash along the scalp, elbows, and knees with overlying excoriation.  Laboratory evaluation reveals the following:

Complete blood count

Hemoglobin: 8.5 g/dL

Reticulocytes: 7%

Platelets: 160,000/mm3

Urinalysis

Blood: moderate

Red blood cells : 0/hpf

Which of the following is the most likely mechanism for this patient's urinary findings?

A. Autoantibody production

B. Oxidative injury

C. Complement activation

D. Immune complex deposition

E. Interstitial leukocyte infiltration

Answer will be posted at 8 PM ET