CSF2 and pulmonary alveolar proteinosis: While autoantibodies against GM-CSF have long been recognised in individuals with Crohn’s disease8, this is by no means a phenocopy of the pulmonary alveolar proteinosis associated with either genetic deficiency of the GM-CSF receptor9 or isolated acquisition of neutralizing autoantibodies to GM-CSF10 and tends to imply a bystander rather than a pathogenic role for anti-GM-CSF autoantibodies in IBD.