Therefore, in the current paradigm, there are three major clinical subtypes of PAP: the most common adult idiopathic variety, which is pre-sumably autoimmune (with a circulating anti–GM-CSF antibody); a neonatal variety that is likely due to a defect in surfactant proteins B or C or the common ß-chain of the GM-CSF receptor; and secondary PAP associated with occupational exposures or immunologic disorders. This evidence concerns the gene CSF2 and pulmonary alveolar proteinosis.