Staining of neutrophils from patients with RA (Fig. 3A) or healthy controls (Fig. 3B) for PAD4 and myosin-9 showed a somewhat variable pattern of co-localization: most of the cytosolic PAD4 staining coincided with myosin-9 staining, but myosin-9 was more widely distributed within neutrophils than PAD4. Here, PADI4 is linked to rheumatoid arthritis.