TNFRSF1A and synovitis: Peripheral synovitis, osteitis, and enthesitis were observed in 100% of the tmTNF+/WT (20/20) as well as in 100% of the tmTNF+/WTxTNF-RII−/− mice (7/7) but not in the tmTNF+/wtxTNF-RI−/− mice (0/9; n > 20; n = 7, and n = 9 respectively; Fig. 7 A), confirming the findings of Alexopoulou et al. (1997) that tmTNF-mediated synovitis induction requires the presence of the TNF-RI.