A 47-year-old man presents to the emergency department with fatigue, hematuria, and shortness of breath. He reports brown-colored urine for the past two days and mild cough with blood-streaked sputum. His past medical history is unremarkable. His blood pressure is 145/90 mmHg, and urinalysis reveals 15 RBC/HPF, proteinuria (300 mg/dL), and red blood cell casts. Serologic testing is positive for anti-glomerular basement membrane (anti-GBM) antibodies. A renal biopsy is performed. Which of the following findings is most likely seen on immunofluorescence microscopy?
