It seems that a “critical threshold” (5 μg ml–1) exists above which anti-GM-CSF antibodies are likely to disrupt GM-CSF-stimulated functions in alveolar macrophages and blood leukocytes [24, 25] and are strongly associated with an increased risk of autoimmune PAP [26]. The gene discussed is CSF2; the disease is autoimmune pulmonary alveolar proteinosis.