PAP is a rare syndrome of surfactant accumulation and resulting hypoxemic respiratory failure that occurs in a number of diseases classified pathogenically into three groups: primary PAP (caused by disruption of GM-CSF signaling - autoimmune PAP, hereditary PAP), secondary PAP (caused by reduction in alveolar macrophage numbers and/or functions), and surfactant dysfunction-related PAP (caused by mutations in genes required for normal surfactant production). In current clinical practice, PAP is diagnosed based on a lung biopsy; an approach that is not able to identify the PAP-causing disease in anyone. Current therapy involves the physical removal of surfactant by a procedure in which the lungs are repeatedly filled with saline and emptied - whole lung lavage, which is invasive, inefficient, and not widely available, especially for children. Importantly, research advances have elucidated the pathogenesis of diseases causing PAP in most patients and have identified new diagnostic and therapeutic approaches. Simple blood-based research tests can now identify the PAP-causing disease in about 95% of patients. Further, several promising potential disease-specific therapies are currently in development. The long-term goals of the Rare Lung Diseases Consortium include improving the diagnosis and therapy of people with PAP. A major goal of this protocol is to conduct a prospective, longitudinal study of autoimmune PAP to examine outcome measures for disease severity for potential use in clinical practice and/or clinical research studies. The investigator's central hypothesis is that a prospective, longitudinal study of autoimmune PAP patients will facilitate the identification of useful outcome measures for use in clinical practice and/or clinical research studies. The specific objectives of the study are to: 1) evaluate blood-based biomarkers of PAP lung disease over time in autoimmune PAP patients, 2) evaluate the natural history/clinical course of autoimmune PAP over time, 3) evaluate quality of life measures over time in autoimmune PAP patients, 4) evaluate physiologic measures of disease over time in autoimmune PAP patients, and 5) evaluate radiologic measures of lung disease progression over time in autoimmune PAP patients. The study design will be observational and will involve recruitment, screening, and enrollment of eligible participants and annual collection of clinical data. The experimental approach will be to assess the rate of change in GM-CSF signaling assay parameters from baseline to 24 months. GM-CSF signaling assay parameters include GM-CSF autoantibody (GMAb) level, pSTAT5-Max, STAT5-phosphorylation index (STAT5-PI), GM-CSF signaling index (GM-SI), and GM-CSF EC50. The study will also assess the progression of autoimmune PAP, including but not limited to use of treatment options, the number and types of infections and other inter-current medical issues with quality of life measures, exercise tolerance, and radiologic imaging. Experimental outcomes will evaluate SP-D, cholestenoic acid, and lipid levels. Anticipated results will establish a natural history/clinical course of autoimmune PAP to better serve patients and providers, to better inform PAP researchers, and validate outcome measures and biomarkers for use in future clinical studies of PAP. These results will impact the field by: 1) improving an understanding of the clinical course of autoimmune PAP, 2) providing information on various clinical outcome and quality of life outcome measures to guide patients and physicians in making treatment choices, and 3) facilitate the development of pharmacotherapeutics for autoimmune PAP and 4) better informing PAP researchers.