A 46-year-old woman has had worsening malaise for the past 36 hours. Her urine output is markedly diminished, and it has a cloudy brown appearance. On examination, she has periorbital edema. Laboratory findings include serum creatinine of 2.8 mg/dL and urea nitrogen of 30 mg/dL. A renal biopsy is performed and on microscopic examination shows focal necrosis in glomeruli with glomerular basement membrane breaks and crescent formation. No immune deposits are identified with immunofluorescence. Which of the following autoantibodies is most likely detectable in her serum?