MPO and rheumatoid arthritis: RA-associated inflammation causes increased synovial permeability, allowing HDL to freely pass into the synovial fluid, and our prior work suggests that HDL may be modified and functionally impaired by the pro-inflammatory leucocyte enzyme myeloperoxidase (MPO), and accumulation of pro-inflammatory oxylipins such as 15-Hydroxyeicosatetraenoic acid (15 HETE) in the RA joint [11].