 The target population is adults with autoimmune PAP who have measurable, clinically significant disease satisfying all of the inclusion and exclusion criteria. The study design will involve recruitment, screening, and enrollment of participants into a phase I, open-label, multi-site study. Sargramostim will be administered to autoimmune PAP patients via aerosol inhalation one time at a dose of 125 mcg or 250 mcg. Adverse events AEs, serious AEs SAEs, PK, and PD parameters will be evaluated see Appendix 3 Schedule of Events. The experimental approach will evaluate 1 safety of inhaled sargramostim by documenting occurrence of treatment-emergent AEs and SAEs, 2 PK profile of GM-CSF in serum and BAL fluid, 3 local and systemic PD effects of inhaled GM-CSF and 4 effects of inhaled GM-CSF on the quality of life for participants. Anticipated results will determine the safety profile of inhaled sargramostim in patients with autoimmune PAP, will evaluate total and free GM-CSF levels in blood and lung, effects of sargramostim on blood and BAL cell counts, differentials, baseline- and GM-CSF-responsiveness of blood leukocytes and BAL cells, and biomarkers of PAP in patients with autoimmune PAP after single dose administration. These results will impact the field by 1 confirming existing published data, 2 monitoring local effects of inhaled sargramostim in autoimmune PAP patients, 3 demonstrating a safe starting dose to evaluate the efficacy of inhaled sargramostim for autoimmune PAP. 