Inthe RA, MPO is consistently detected at high concentrations in patients’synovial fluid and serum and has been implicated in bone erosion andjoint degradation.−, ,  Here, we observed markedly elevated MPO activity in the paw tissueof both young and aged rats following CFA administration, reinforcingthe role of MPO as a critical mediator in RA pathophysiology. This evidence concerns the gene MPO and rheumatoid arthritis.