MPO and rheumatoid arthritis: They participate in the inflammation and bone erosion of RA by releasing TNF, IL-1β, IL-6 and other cytokines, as well as matrix metalloproteinase-9 (MMP-9), myeloperoxidase (MPO) (Strzepa et al., 2017) and neutrophil elastase (NE) (Krotova et al., 2020), which degrade the extracellular matrix to impair joints (Chen et al., 2018).