MMP9 and rheumatoid arthritis: Moreover, a 7-biomarker signature consisting of MMP-1, MMP-2, MMP-7, MMP-9, IL-1 receptor antagonist, soluble CD40L, and CXCL9 effectively differentiated RA-ILD from RA–no ILD with high sensitivity and specificity in a separate cohort, yielding an AUC of 0.9310.