Serial Anti-GM-CSF Autoantibody Levels Reflect Disease Activity in Hypersensitivity Pneumonitis with Autoimmune Pulmonary Alveolar Proteinosis: Case Report

Autoimmune pulmonary alveolar proteinosis (aPAP) is characterized by the accumulation of phospholipids and surfactant proteins in the peripheral air spaces due to alveolar macrophage dysfunction caused by anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies (GMAb). Hypersensitivity pneumonitis (HP) is a granulomatous lung disease associated with GM-CSF. In this report, we evaluated serial changes in serum GMAb levels in a 67-year-old male current smoker with HP and aPAP and examined their correlation with HP disease activity. GMAb levels increased at HP onset and decreased after HP remission with oral prednisolone therapy. After the first remission, the patient experienced three relapses and remissions. Although GMAb levels were not evaluated for all HP relapses and remissions, GMAb levels increased at one relapse but decreased at two remissions induced by the oral prednisolone therapy. Pulmonary fibrosis progressed, and the patient died of pneumonia. GMAb was at its almost normal levels at 8 months before the onset of pneumonia. We hypothesized that GMAbs may have been induced to improve HP through neutralizing GM-CSF. Although the hypothesis needs to be confirmed in additional patients, serial measurement of GMAb may be useful for a better understanding of the pathophysiology and deciding the appropriate treatment for HP with aPAP.