A 44-Year-Old Man Comes to the Physician Because of a Productive

A 44-year-old man comes to the physician because of a productive cough consisting of tenacious sputum for the last 2 weeks.  He denies fever, chills, wheezes, shortness of breath, and chest pain.  He reports getting "bronchitis" and "sinus infections" almost every year for the past five years that subside with antibiotic therapy.  He attributes his infections to his smoking, which he has cut down to a half-pack per day over the past year.  He was admitted to the hospital for pneumonia one year ago and was treated with intravenous antibiotics.  He reports that he was "a healthy child" and received all of his childhood immunizations.  There is no family history of lung disease.
His blood pressure is 122/70 mm Hg and his pulse is 89/min and regular.  Oxygen saturation is 95% on room air.  Examination reveals scattered rhonchi at the right lung base.  There is no sinus tenderness.  The nasal turbinates look normal.  There is no finger or toe clubbing.
Complete blood count with differential is within normal limits.  Chest x-ray shows linear atelectasis at the right lung base.  Multi-slice CT scan of the chest shows dilation and wall thickening of the right lower lobe bronchi with adjacent areas of fibrosis and possible parenchymal consolidation.
Two sputum cultures from different samples grow Haemophilus influenzae, and acid-fast staining is negative.  PPD skin testing shows 3 mm induration after 48 hours.
After three days of antibiotic therapy, the patient reports marked improvement of his symptoms.
Which of the following is the most appropriate next step in management?

A) Alpha-1 antitrypsin levels
B) Bronchoscopy with transbronchial biopsy
C) Immediate skin test reactivity to Aspergillus antigens
D) Serum immunoglobulin quantitation
E) Smoking cessation and repeat CT scan of the chest in 12 months