21. A 70-year-old man is brought to the emergency department because of a 3-day history of fever and progressive shortness of breath. He also has a history of cough productive of yellow sputum that has recently become thick and green. He has smoked 1 to 2 packs of cigarettes daily for 40 years. His temperature is 40°C (104°F), and respirations are 22/min. Physical examination shows decreased breath sounds. A chest x-ray shows right lower lobe infiltrates surrounding a 3-cm, rounded lesion containing an air-fluid level. Which of the following immune cell activities most likely predominates in the center of this lesion? A) B-lymphocyte antibody production B) Macrophage free-radical generation C) Natural killer cell-mediated killing D) Segmented neutrophil acid hydrolase activation E) T-lymphocyte perforin synthesis D

21. A 70-year-old man is brought to the emergency department because of a 3-day history of fever and progressive shortness of breath. He also has a history of cough productive of yellow sputum that has recently become thick and green. He has smoked 1 to 2 packs of cigarettes daily for 40 years. His temperature is 40°C (104°F), and respirations are 22/min. Physical examination shows decreased breath sounds. A chest x-ray shows right lower lobe infiltrates surrounding a 3-cm, rounded lesion containing an air-fluid level. Which of the following immune cell activities most likely predominates in the center of this lesion? A) B-lymphocyte antibody production B) Macrophage free-radical generation C) Natural killer cell-mediated killing D) Segmented neutrophil acid hydrolase activation E) T-lymphocyte perforin synthesis D