MUC1 and interstitial lung disease: In subsequent investigations, elevated serum levels of KL-6 were shown to be present in a greater proportion of patients with ILD compared with other reported disease biomarkers, including sialyl-Lewis a (sLea), sialyl-Lewis x (sLex), surfactant protein-A, surfactant protein-D, monocyte chemoattractant protein-1 (MCP-1), and C-C motif chemokine ligand 18 (CCL18) (171–174).