MUC1 and pulmonary fibrosis: ILD, interstitial lung diseases; CTD-ILD, connective tissue disease-associated interstitial lung disease; fHP, fibrotic hypersensitivity pneumonitis; NSIP, nonspecific interstitial pneumonia; IPF, idiopathic pulmonary fibrosis; MMP7, matrix metalloproteinase 7; KL-6, Krebs von den Lungen-6