Light chain (κ/λ) ratio of GM-CSF autoantibodies is associated with disease severity in autoimmune pulmonary alveolar proteinosis

- Neither concentration nor binding avidity correlated with the severity in aPAP.
- The κ/λ ratio of GMAb in aPAP patients was higher than those of total IgG.
- The κ/λ ratio of GMAb was significantly correlated with PaO2, AaDO2, and DSS.
- The light chain usage of GMAb may represent a disease severity marker in aPAP.

Previous studies demonstrated that antigranulocyte colony-stimulating factor autoantibody (GMAb) was consistently present in patients with autoimmune pulmonary alveolar proteinosis (aPAP), and, thus, represented candidature as a reliable diagnostic marker. However, our large cohort study suggested that the concentration of this antibody was not correlated with disease severity in patients. We found that the κ/λ ratio of GMAb was significantly correlated with the degree of hypoxemia. The proportion of λ-type GMAb per total λ-type IgG was significantly higher in severely affected patients than those in mildly affected patients, but the proportion of κ-type was unchanged. The κ/λ ratio was significantly correlated with both KL-6 and SP-D, which have been previously reported as disease severity markers. Thus, the light chain isotype usage of GMAb may not only be associated with the severity of aPAP, but may also represent a useful disease severity marker.