Administration of a non-selective PAD inhibitor (bb-chloride-amidine) significantly decreased the protein expression of alpha-smooth muscle actin (α-SMA) (Fig. 2A) and reduced the gel contraction area (i.e., greater gel surface area due to reduced contraction) (Fig. 2B) of RA-ILD fibroblasts compared to vehicle-treated cells, both markers of myofibroblast differentiation. The gene discussed is ACTA1; the disease is rheumatoid arthritis.