Periodic Acid Schiff (PAS) stain positive intra-alveolar material is seen in

Periodic Acid Schiff (PAS) stain positive intra-alveolar material is seen in Pulmonary Alveolar Proteinosis Most common cause of PAP is an autoimmunity to GM-CSF, a critical factor in development of alveolar macrophages. Decreased bioavailability of GM-CSF results in poor alveolar macrophages development and function, which results in accumulation of surfactant and related products. Secondary causes of PAP are those in which the accumulation of lipoproteinaceous compounds is secondary to another disease process. PAS material in alveoli is accumulated surfactant due to decreased turnover in pulmonary alveolar proteinosis. The same material may be coughed up by patients and described as chunky gelatinous plugs. PAS stain positivity on histology