TNF and Arthritis: To evaluate the potential origins of these iron-rich macrophages, we next assessed ankle joints by Prussian blue staining, which showed a corresponding dramatic increase in iron-laden macrophages in the synovium of TNF-Tg mice with Advanced arthritis (Figures 4H–J; WT 163.3 ± 117.7 vs Early 7850 ± 6090 vs Advanced 31897 ± 16007 μm2 of Prussian blue in the peri-talus region; p<0.001).