A Randomized, Double-Blinded, Placebo-Controlled, Phase II Inhaled Interferon Gamma-1b and Antimycobacterials to Treat Pulmonary Mycobacterium Avium Complex Infections

This study will test the safety and effectiveness of inhaled interferon gamma-1b and oral antibiotics for treating mycobacterium avium complex (MAC) infection of the lungs. Patients 18 years of age or older with MAC infection of the lungs who 1) have been previously treated for MAC, or 2) have moderate or severe lung disease due to MAC that has not been previously treated may be eligible for this study. Participants will be randomly assigned to one of two treatment groups. Group 1 will receive 500 micrograms of interferon gamma-1b 3 times a week for 48 weeks by inhalation. Group 2 will inhale a placebo (inactive substance) according to the same regimen. In addition, all patients will receive standard MAC treatment with three antibiotics-clarithromycin or azithromycin, ethambutol and rifampin or rifabutin-taken by mouth times a week. Patients will come to the clinic for a screening visit, baseline visit, 1 month after beginning treatment, and at 3-month intervals thereafter until the end of the study. During these various visits, they will undergo the following tests and procedures: * Medical history and physical examination, including height and weight measurements, heart rate, breathing rate, blood pressure and temperature * Possibly computed tomography (CT) and X-ray of the lungs * Sputum sample * Pulmonary function studies * Blood and urine tests Patients' eyes will be examined monthly to check for side effects of ethambutol, and hearing and balance will be tested to check for side effects of clarithromycin or azithromycin. At the baseline visit, the patient or caretaker will be trained to use a nebulizer (a special breathing device) to take the study medication.