Objective: Determine the safety and efficacy of GM-CSF inhalation in patients with aPAP.

Study Design: multi-center, randomized, double-blind, placebo- controlled, safety/efficacy study.

Inclusion Criteria:

1. Age over 16 years and below 80 years (as of the date of registration).
2. Can provide signed informed consent.
3. Willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures specified in the protocol (including short-term hospital admission).
4. Autoimmune pulmonary alveolar proteinosis diagnosed by both HR-CT and biopsy and/or BAL as well as GM-CSF antibodies in serum positive.
5. PaO2 < 70 mmHg after 5 minutes spine position at room air, or PaO2 < 75 mmHg after 5 minutes spine position at room air and with symptom(s) including cough, sputum and exertional dyspnea

Exclusion Criteria:

1. Diagnosed as secondary or hereditary pulmonary alveolar proteinosis
2. WBC of 12,000/mm3 or more
3. Fever of 38 degree celsius or more
4. Severe edema
5. History of malignant disease within recent 5 years (not applied to the treated cases of uterine carcinoma in situ and local basal cell carcinoma)
6. Complication of cardiovascular diseases including congestive heart failure, angina pectoris, hemorrhagic tendency, etc with severe condition.
7. Complication of respiratory diseases such as pulmonary infectious disease(incl. pulmonary tuberculosis), bronchial asthma, lung fibrosis ,interstitial pneumonitis, or bronchiectasis, in which the evaluations of safety and efficacy of GM-CSF therapy are considered as difficult.
8. History or complication of infectious diseases which require systemic administration of antibiotics, antifungal or antiviral agents within recent 2 weeks.
9. Treatment with other cytokines
10. Pregnant or possibly pregnant women, lactating women, and women who desire to become pregnant during the study period
11. Patients who have been treated with whole-lung lavage, repeated segmental-lung lavage, or rituximab within 6 months before the start of the study (this criterion does not apply to patients for whom 6 months or more have elapsed after their last lavage or rituximab)
12. Severe liver dysfunction (AST > 100 IU/L and/or ALT > 100 IU/L and/or T-bil >3.0mg/dL)
13. Severe renal dysfunction (Ccr < 30 mL/min, calculated by Cockcroft-Gault (CG) formula)
14. Previous experience of severe and unexplained side-effects during aerosol delivery of any kind of medicinal product
15. Treatment with oral or intravenous administration or inhalation of corticosteroids.
16. Treatment with other inhaled drugs.
17. Previously treated with GM-CSF before the start of the study.
18. Demonstrate hypersensitivity to GM-CSF agent.
19. Other patients judged to be inappropriate for the study by the attending physician (e.g., patients who are unlikely to complete treatment or are uncooperative).