MUC1 and interstitial lung disease: Supporting this, a systematic review identified multiple serum-based indicators—including anti-citrullinated protein antibodies (ACPAs) [48], KL-6 [51,52], matrix metalloproteinase-13 (MMP-13), and C-X-C motif chemokine ligand 11/interferon-inducible T cell alpha chemoattractant (CXCL11/I-TAC)—as being associated with progressive disease in RA-ILD [49].