PRF1 and rheumatoid arthritis: Increasing evidence indicates that the abnormal expression of GZM family, granule proteins (NKG5 and NKG7), and perforin one (PRF1) is involved in a number of autoimmune diseases, including ankylosing spondylitis, rheumatoid arthritis (RA), hypersensitive pneumonitis, celiac disease, and scleroderma (Anthony et al., 2010; Prager et al., 2019).