Affinity- and epitope-dependent pathogenicity of GM-CSF autoantibodies in patients with autoimmune pulmonary alveolar proteinosis.

Summary

By generating and functionally characterizing 186 monoclonal GM-CSF autoantibodies from 28 aPAP patients, the authors show that epitope class and affinity dictate neutralization potency and clinical pathogenicity. High-affinity class 1 antibodies are enriched in severe disease and alone trigger PAP-like pathology in a humanized mouse, explaining the poor correlation between total antibody titers and disease severity.

Key Findings

• Generated 186 monoclonal GM-CSF autoantibodies from 28 aPAP patients and classified them into class 1 (A/BD/D epitopes) and class 2 (B/C epitopes).
• In class 1 antibodies, affinity strongly correlated with neutralization; this correlation was weak/absent in class 2.
• High-affinity class 1 antibodies were enriched in patients with more severe disease and were sufficient to induce PAP in a humanized mouse model.
• Findings explain why total serum GM-CSF autoantibody titers fail to reflect disease severity.

Clinical Implications

Epitope/affinity profiling could refine risk stratification, guide timing and intensity of B-cell‒directed therapies or plasmapheresis, and inform development of epitope-specific neutralizing decoys.

Limitations

• Cohort size is modest and drawn from specialized centers; generalizability requires broader populations.
• Duration and standardized clinical endpoints of longitudinal follow-up are not detailed in the abstract.

Future Directions

Develop clinical assays for rapid epitope/affinity profiling; prospectively test whether these metrics predict outcomes and response to B-cell depletion or plasmapheresis; explore epitope-specific decoy or tolerance-inducing therapies.