TSPO and Arthritis: Although all groups of MDM demonstrated a significant increase in TSPO expression compared to their monocyte counterparts (p<0.01), the magnitude of TSPO up-regulation was greater in MDM derived from the synovial fluid of arthritis patients (mean fold change of 284.6 ± 27.88 on synovial fluid MDM compared to synovial fluid monocytes, versus mean fold change 65.4 ± 16.88 for healthy peripheral blood MDM compared to healthy monocytes; Fig 1B and 1C).