SFTPD and acute respiratory distress syndrome: Additional epithelial cell-derived molecules that represent candidate ARDS biomarkers include sialylated carbohydrate antigen Krebs von den Lungen-6 (KL-6, a fragment of MUC1 mucin), surfactant protein B (SP-B)[39], surfactant protein D (SP-D)[25, 26, 40], Clara cell protein CC-16[41], and the gamma-2 chain of laminin-5 (an extracellular matrix protein with cell adhesive properties)[42].