In PAP with no comorbidity, the first cluster contained IL-2, IL-17E, IL-9, IL-28A, IL-23, TNFα, IFNγ, IL-13, while the second cluster contained GM-CSF, IL-15, CCL20, IL-10, IL-21, IL-6, IL-33, and IL-27 (Fig. 5b). Here, IL21 is linked to pulmonary alveolar proteinosis.