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?

A 28-year-old male reports a 1-week history of fatigue, cough, and shortness of breath. Two days ago, he began coughing up blood-streaked sputum and noticed dark, tea-colored urine. He denies recent fever or upper respiratory symptoms but mentions mild weight loss over the last month. There is no history of recent travel or sick contacts. The patient is a smoker (1 pack/day for 5 years) and works in construction. He denies drug use or recent exposure to chemicals. Past Medical History: No known chronic conditions No previous episodes of hemoptysis or kidney problems Medications: None Family History: No significant history of autoimmune diseases or kidney problems Physical Examination: • Vital Signs: BP 160/95 mmHg, HR 105 bpm, RR 24/min, SpO₂ 91% on room air • General: Mildly pale, fatigued • Respiratory: Bilateral crackles at lung bases • Cardiovascular: Tachycardia without murmurs • Abdomen: No tenderness or organomegaly • Extremities: No edema • Skin: No rashes Initial Laboratory Results: • Hemoglobin: 9.0 g/dL (low) • Hematocrit: 28% • Platelet count: Normal • Serum creatinine: 3.0 mg/dL (elevated) • BUN: 45 mg/dL (elevated) • Urinalysis: Hematuria, proteinuria, red blood cell casts • Serum anti-GBM antibodies: Positive • ANA, ANCA: Negative Imaging: • Chest X-ray: Bilateral alveolar infiltrates consistent with pulmonary hemorrhage • Renal ultrasound: Normal-sized kidneys Renal Biopsy: • Light microscopy: Crescent formation in glomeruli • Immunofluorescence: Linear deposition of IgG along the glomerular basement membrane Which of the following best explains the mechanism of this disease?

A 25-year-old man presents to the emergency department with hemoptysis, hematuria, and fatigue. He reports a recent upper respiratory infection two weeks ago. Physical examination reveals mild pallor and bibasilar crackles on lung auscultation. Chest X-ray shows bilateral alveolar infiltrates, and urinalysis reveals hematuria and proteinuria. Laboratory testing demonstrates: Serum creatinine: 3.2 mg/dL (elevated) Anti-glomerular basement membrane (anti-GBM) antibodies: Positive Renal biopsy: Linear IgG deposits along the glomerular basement membrane on immunofluorescence Which of the following best describes the hypersensitivity reaction responsible for this patient’s condition?

Patient: 7-year-old female Chief Complaint: Recurrent respiratory infections and chronic diarrhea. History of Present Illness: The patient has experienced multiple episodes of otitis media, sinusitis, and pneumonia since infancy. Over the past year, she has had three hospitalizations for pneumonia requiring intravenous antibiotics. Additionally, she has suffered from chronic diarrhea for the past six months, leading to weight loss and growth delays. There is no history of skin infections or abscesses. Past Medical History: • No known chronic illnesses. • Incomplete vaccination history due to frequent illnesses. Medications: • Occasional courses of antibiotics for infections. Family History: • Non-consanguineous parents. • No family history of immunodeficiency or recurrent infections. Social History: • Attends school; frequent absences due to illness. • No exposure to tobacco smoke or known environmental hazards. Physical Examination: • Vital Signs: Temperature: 37.8°C; Heart Rate: 110 bpm; Respiratory Rate: 22/min; Blood Pressure: 100/60 mmHg. • General: Pale, thin, and appears fatigued. • Growth Parameters: Below the 5th percentile for age in both height and weight. • HEENT: Mild cervical lymphadenopathy; tympanic membranes dull with mild erythema bilaterally. • Respiratory: Crackles heard in the right lower lung field. • Abdomen: Soft, non-tender; mild hepatomegaly noted. • Skin: No rashes or lesions. Laboratory Investigations: • Complete Blood Count (CBC): • Hemoglobin: 10.5 g/dL (low) • White Blood Cell Count: 6,000/µL • Platelets: 250,000/µL • Serum Immunoglobulins: • IgM: Elevated • IgG: Low • IgA: Low • Flow Cytometry: • Normal B and T cell numbers. • Genetic Testing: • Homozygous mutation identified on chromosome 20 • Stool Analysis: • Positive for Cryptosporidium antigen. What is the most likely diagnosis?