 PAP occurs as primary, secondary, congenital and idiopathic forms. RLDC investigators have previously shown that primary PAP is strongly associated with high levels of circulating, neutralizing anti-GM-CSF autoantibodies. Absence of GM-CSF bioactivity is thought to impair alveolar macrophage and blood neutrophil functions including reduced surfactant catabolism alveolar macrophages - thought to result in surfactant accumulation in primary PAP and immune dysfunction neutrophil dysfunction, and possibly macrophage dysfunction - thought to increase the risk of infection in primary PAP. Secondary PAP is caused by an underlying condition believed to impair alveolar macrophage surfactant catabolism. Secondary PAP is related to other conditions, including myelogenous leukemias, infections and environmental exposures. Congenital PAP is caused by mutations in the genes encoding surfactant protein SP-B, SP-C or the ABCA3 transporter. Idiopathic PAP is that which results from unknown mechanisms. Anti-GM-CSF autoantibodies appear to be absent in secondary, congenital and idiopathic PAP. 