In the pathogenesis of PAP, GM-CSF signaling is impaired due to defects in GM-CSF or its receptor, or the presence of anti-GM-CSF autoantibodies, which fail to induce the expression of PU.1 and PPAR-γ, resulting in abnormal development and function of AMs. The gene discussed is SPI1; the disease is pulmonary alveolar proteinosis.